What Happened Before The Big Bang?

“The aim of science is not to open the door to infinite wisdom, but to set a limit to infinite error.” -Bertolt Brecht

One of the most frequent questions I get about the Universe — as a cosmologist — isn’t quite about the Big Bang in and of itself.

The expansion of the Universe in reverse; image source unknown.

The Big Bang is a remarkable idea, of course, that says that, based on the observations that the Universe is expanding and cooling today, it was hotter, denser, and physically smaller in the past. This gets particularly exciting when we extrapolate very far back in the history of the Universe.

Image credit: Addison Wesley.

At some point in the past, it was so hot that individual atoms would have been blasted apart by the radiation in the Universe. This means that — as we come forward in time past that point — there was a point when all the nuclei and electrons in the Universe became stable, neutral atoms for the first time.

Image credit: Pearson / Addison Wesley, retrieved from Jill Bechtold.

And before that, it was so hot that individual nuclei would have been blasted apart. But you might think that this means we can go back to arbitrarily high temperatures, densities, and arbitrarily small sizes. You might be tempted to go all the way to a point in time where spacetime collapses into a singularity, and where all the matter and energy in the Universe were present at a single point, of infinite temperature and infinite density.

Image retrieved from University of Arizona. And yes, longtime readers, this is wrong.

Indeed, this is one of the most tempting things to try.
But physically, it’s also wrong. (Lots of good scientists and science institutions goof this, too.) You see, we know that this isn’t what happened in the Universe’s past, because of what we observe when we look — in detail — at a snapshot of the Universe’s early history, from back when those neutral atoms formed for the first time.

What we learn is that there’s an upper limit to how hot the Universe ever was in its early history. And although it may have been very hot — up to energies between 10^16 and 10^17 GeV, or about 10 trillion times hotter than the Large Hadron Collider can create — that’s actually quite small compared to the scale where we’d need to talk about singularities (which is another factor of ~1000 hotter), or where quantum gravity/string theory effects would become important.
We learn this from looking at the magnitude and distribution of the temperature fluctuations in the Universe imprinted in the snapshot alluded to earlier: in the Cosmic Microwave Background.

Image credit: NASA / WMAP science team; in a projection the way you'd see a globe.

(If you prefer a Mercator projection — the way you typically see a map of Earth)
What these fluctuations tell us is that, at some point in the very early history of the Universe — where we can be accurately described by this hot, dense, radiation-filled, Big Bang-esque model — the Universe was filled with small-magnitude temperature fluctuations (of a few parts in 100,000) on all measurable scales, where each scale is observed to have the same-magnitude pattern of fluctuations.

Image credit: Chiang Lung-Yih, doing a spherical harmonic decomposition of the CMB data.

As the Universe expands and cools, gravity works to pull the matter and energy in on itself, making overdensities bigger and underdensities smaller, while radiation pressure works to wash those fluctuations out. Normal matter (protons, neutrons, and electrons) interacts with photons and itself, creating “bouncy” features in this pattern of fluctuations, while dark matter can feel the radiation pressure and the gravitational tugs, but has no cross-section with either normal matter, photons or itself.
As a result, we learn what the different components of the Universe are.

Image credit: WMAP / NASA; Ned Wright of http://www.astro.ucla.edu/~wright/CMB-DT.html.

Two important observations that come out of this are that, as far as curvature goes, the Universe is spatially flat, rather than curved positively (like a sphere) or negatively (like the seat of a saddle), and that it has the same temperature properties in all directions, even in regions that have never had an opportunity to exchange information (or transmit photons) between one another.

Images credit: horizon problem (top) via astronomynotes.com; flatness problem (bottom) by Ned Wright's cosmology tutorial.

These two things could be remarkable, finely-tuned coincidences (or, you know, just how things happen to be, for no reason), but they could also be indicative of something preceding the Big Bang. In particular, a phase of exponential expansion of the Universe — known as cosmological inflation — would compel these two things to be true. But cosmic inflation also carries a number of predictions with it: that there would be no magnetic monopoles or other leftover relics from grand unified theories, that there would be no topological defects (e.g., cosmic strings, domain walls) in the large scale structure of the Universe, and that the temperature fluctuations found in the Cosmic Microwave Background would follow a special type of distribution.

Image credit: Takeo Moroi & Tomo Takahashi, from http://arxiv.org/abs/hep-ph/0110096.

Not only do we find strong evidence against leftover relics and topological defects, but we measured this Harrison-Zel’dovich spectrum very accurately back in the 1990s, which was predicted by inflation more than a decade before it was observed! In other words, the spectrum of fluctuations is precisely consistent with what the theory of cosmological inflation predicted!
What inflation — our best scientific theory as to what preceded the Big Bang — tells us about “what came before the Big Bang” is, perhaps, very surprising.

Image generated by me, of the scale of the Universe (y-axis) vs. time (arbitrary units).

If the Universe was filled with matter (orange) or radiation (blue), as shown above, there must be a point at which these infinite temperatures and densities are reached, and thus, a singularity. But in the case of inflation (yellow), everything changes. First off, we don’t necessarily have a singularity, and we definitely don’t have one at what we traditionally think of as “the moment of the Big Bang.” Instead, we have what’s known as a past-timelike-incomplete spacetime.

Image generated by me, of the scale of the Universe (y-axis) vs. time (arbitrary units).

In other words, we not only don’t know whether there was a singularity at some point in the very distant, pre-inflation past, or whether inflation was truly eternal, we don’t even know whether inflation occurred for less than a yoctosecond or more than the present age of the (post-Big Bang) Universe!
Our prospects for finding out, furthermore, are quite dim, as — by its very nature — practically every model of cosmic inflation wipes out any information about the Universe that existed prior to the last billionth-of-a-yoctosecond before inflation ended, and our Universe began.

Image credit: Cosmic Inflation by Don Dixon.

So, before the Universe was hot, dense, expanding, cooling, and filled with matter and antimatter? There was inflation, the phase of exponential expansion that stretched the Universe flat, made it the same average temperature in all directions, wiped out any ultra-massive relic particles and topological defects, created the temperature fluctuations that led to the large-scale structure of today’s Universe, and ended 13.7 billion years ago, setting up the Big Bang that gave rise to the observable Universe we know and love. If inflation lasted any longer than that last billionth-of-a-yoctosecond that affects our observable Universe and the laws of physics we know still hold, then we almost certainly live in a multiverse as well, where our observable Universe is just one Universe out of many.

Image credit: Me, illustrating how an inflating region of spacetime's exponential properties will create new spacetime more quickly than the dynamics that end inflation can create Big Bangs and matter/radiation-filled regions of our Universe!

But what came before that? We only have theoretical possibilities, with likely no data or information from that time contained within our observable Universe to guide us. We’ll keep searching for clues, but for right now, don’t believe the hype (and I’m looking at you, Steinhardt, Turok, and Greene, among others); keep them as possibilities if you fancy them, but that speculation is no replacement for the best that science has to offer right now!

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The Big Bang

The Big Bang

The night sky presents the viewer with a picture of a calm and unchanging Universe. So the 1929 discovery by Edwin Hubble that the Universe is in fact expanding at enormous speed was revolutionary. Hubble noted that galaxies outside our own Milky Way were all moving away from us, each at a speed proportional to its distance from us. He quickly realized what this meant that there must have been an instant in time (now known to be about 14 billion years ago) when the entire Universe was contained in a single point in space. The Universe must have been born in this single violent event which came to be known as the "Big Bang."
Astronomers combine mathematical models with observations to develop workable theories of how the Universe came to be. The mathematical underpinnings of the Big Bang theory include Albert Einstein's general theory of relativity along with standard theories of fundamental particles. Today NASA spacecraft such as the Hubble Space Telescope and the Spitzer Space Telescope continue Edwin Hubble's work of measuring the expansion of the Universe. One of the goals has long been to decide whether the Universe will expand forever, or whether it will someday stop, turn around, and collapse in a "Big Crunch?"

The structure of the universe evolved from the Big Bang, as represented by WMAP's "baby picture", through the clumping and ignition of matter (which caused reionization) up to the present.

Background Radiation
According to the theories of physics, if we were to look at the Universe one second after the Big Bang, what we would see is a 10-billion degree sea of neutrons, protons, electrons, anti-electrons (positrons), photons, and neutrinos. Then, as time went on, we would see the Universe cool, the neutrons either decaying into protons and electrons or combining with protons to make deuterium (an isotope of hydrogen). As it continued to cool, it would eventually reach the temperature where electrons combined with nuclei to form neutral atoms. Before this "recombination" occurred, the Universe would have been opaque because the free electrons would have caused light (photons) to scatter the way sunlight scatters from the water droplets in clouds. But when the free electrons were absorbed to form neutral atoms, the Universe suddenly became transparent. Those same photons - the afterglow of the Big Bang known as cosmic background radiation - can be observed today.

Missions Study Cosmic Background Radiation

NASA has launched two missions to study the cosmic background radiation, taking "baby pictures" of the Universe only 400,000 years after it was born. The first of these was the Cosmic Background Explorer (COBE). In 1992, the COBE team announced that they had mapped the primordial hot and cold spots in cosmic background radiation. These spots are related to the gravitational field in the early Universe and form the seeds of the giant clusters of galaxies that stretch hundreds of millions of light years across the Universe. This work earned NASA's Dr. John C. Mather and George F. Smoot of the University of California the 2006 Nobel Prize for Physics.
The second mission to examine the cosmic background radiation was the Wilkinson Microware Anisotropy Probe (WMAP). With greatly improved resolution compared to COBE, WMAP surveyed the entire sky, measuring temperature differences of the microwave radiation that is nearly uniformly distributed across the Universe. The picture shows a map of the sky, with hot regions in red and cooler regions in blue. By combining this evidence with theoretical models of the Universe, scientists have concluded that the Universe is "flat," meaning that, on cosmological scales, the geometry of space satisfies the rules of Euclidean geometry (e.g., parallel lines never meet, the ratio of circle circumference to diameter is pi, etc).
A third mission, Planck, led by the European Space Agency with significant participation from NASA, was. launched in 2009.  Planck is making the most accurate maps of the microwave background radiation yet. With instruments sensitive to temperature variations of a few millionths of a degree, and mapping the full sky over 9 wavelength bands, it measures the fluctuations of the temperature of the CMB with an accuracy set by fundamental astrophysical limits.

The Universe's "baby picture". WMAP's map of the temperature of the microwave background radiation shows tiny variations (of few microdegrees) in The 3K background. Hot spots show as red, cold spots as dark blue.

Inflation
One problem that arose from the original COBE results, and that persists with the higher-resolution WMAP data, was that the Universe was too homogeneous. How could pieces of the Universe that had never been in contact with each other have come to equilibrium at the very same temperature? This and other cosmological problems could be solved, however, if there had been a very short period immediately after the Big Bang where the Universe experienced an incredible burst of expansion called "inflation." For this inflation to have taken place, the Universe at the time of the Big Bang must have been filled with an unstable form of energy whose nature is not yet known. Whatever its nature, the inflationary model predicts that this primordial energy would have been unevenly distributed in space due to a kind of quantum noise that arose when the Universe was extremely small. This pattern would have been transferred to the matter of the Universe and would show up in the photons that began streaming away freely at the moment of recombination. As a result, we would expect to see, and do see, this kind of pattern in the COBE and WMAP pictures of the Universe.
But all this leaves unanswered the question of what powered inflation. One difficulty in answering this question is that inflation was over well before recombination, and so the opacity of the Universe before recombination is, in effect, a curtain drawn over those interesting very early events. Fortunately, there is a way to observe the Universe that does not involve photons at all. Gravitational waves, the only known form of information that can reach us undistorted from the instant of the Big Bang, can carry information that we can get no other way. Two missions that are being considered by NASA, LISA and the Big Bang Observer, will look for the gravitational waves from the epoch of inflation.

 Dark Energy

During the years following Hubble and COBE, the picture of the Big Bang gradually became clearer. But in 1996, observations of very distant supernovae required a dramatic change in the picture. It had always been assumed that the matter of the Universe would slow its rate of expansion. Mass creates gravity, gravity creates pull, the pulling must slow the expansion. But supernovae observations showed that the expansion of the Universe, rather than slowing, is accelerating. Something, not like matter and not like ordinary energy, is pushing the galaxies apart. This "stuff" has been dubbed dark energy, but to give it a name is not to understand it. Whether dark energy is a type of dynamical fluid, heretofore unknown to physics, or whether it is a property of the vacuum of empty space, or whether it is some modification to general relativity is not yet known.

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Thermodynamic Laws

 








A thermodynamic system is one that
interacts and exchanges energy with
the area around it. The exchange and
transfer need to happen in at least two
ways. At least one way must be the
transfer of heat. If the thermodynamic
system is "in equilibrium," it can't
change its state or status without
interacting with its environment. Simply
put, if you're in equilibrium, you're a
"happy system," just minding your own
business. You can't really do anything. If
you do, you have to interact with the
world around you.

A Zeroth Law?

The zeroth law of thermodynamics will be
our starting point. We're not really sure
why this law is the zeroth. We think
scientists had "first" and "second" for a
long time, but this new one was so
important it should come before the
others. And voila! Law Number Zero!
Here's what it says: When two systems
are sitting in equilibrium with a third
system, they are also in thermal
equilibrium with each other.
In English: systems "One" and "Two" are
each in equilibrium with "Three." That
means they each have the same energy
content as "Three". But if THAT’S true,
then all the values found in "Three",
match those in both "One" and "Two".
It’s obvious, then, that the values of
"One" and "Two" must ALSO match. This
means that "One" and "Two" have to be
in equilibrium with each other.

A First Law

The first law of thermodynamics is a little
simpler. The first law states that when
heat is added to a system, some of that
energy stays in the system and some
leaves the system. The energy that
leaves does work on the area around it.
Energy that stays in the system creates
an increase in the internal energy of the
system.
In English: you have a pot of water at
room temperature. You add some heat to
the system. First, the temperature and
energy of the water increases. Second,
the system releases some energy and it
works on the environment (maybe
heating the air around the water, making
the air rise).

A Second Law

The big finish! The second law of
thermodynamics explains that it is
impossible to have a cyclic (repeating)
process that converts heat completely
into work. It is also impossible to have a
process that transfers heat from cool
objects to warm objects without using
work.
In English: that first part of the law says
no reaction is 100% efficient. Some
amount of energy in a reaction is always
lost to heat. Also, a system can not
convert all of its energy to working
energy.
The second part of the law is more
obvious. A cold body can't heat up a
warm body. Heat naturally wants to flow
from warmer to cooler areas. Heat wants
to flow and spread out to areas with less
heat. If heat is going to move from cooler
to warmer areas, it is going against what
is “natural”, so the system must put in
some work for it to happen.

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THE PARADOXES OF TIME TRAVEL

TIME travel, I maintain, is possible. The paradoxes of
time travel are oddities, not impossibilities. They
prove only this much, which few would have doubted:
that a possible world where time travel took place would
be a most strange world, different in fundamental ways
from the world we think is ours.
I shall be concerned here with the sort of time travel
that is recounted in science fiction. Not all science fiction
writers are clear-headed, to be sure, and inconsistent
time travel stories have often been written. But some
writers have thought the problems through with great
care, and their stories are perfectly consistent.
If I can defend the consistency of some science fiction
stories of time travel, then I suppose parallel defenses
might be given of some controversial physical hypotheses,
such as the hypothesis that time is circular or the
hypothesis that there are particles that travel faster than
light. But I shall not explore these parallels here.
What is time travel? Inevitably, it involves a discrepancy
between time and time. Any traveler departs and
then arrives at his destination; the time elapsed from departure
to arrival (positive, or perhaps zero) is the duration
of the journey. But if he is a time traveler, the
separation in time between departure and arrival does
not equal the duration of his journey. He departs; he travels
for an hour, let us say; then he arrives. The time he
reaches is not the time one hour after his departure. It
is later, if he has traveled toward the future; earlier, if he
has traveled toward the past. If he has traveled far toward
the past, it is earlier even than his departure. How
can it be that the same two events, his departure and his
arrival, are separated by two unequal amounts of time?
It is tempting to reply that there must be two independent
time dimensions; that for time travel to be possible,
time must be not a line but a plane.Then a pair of events may have two unequal separations if they are
separated more in one of the time dimensions than in
the other. The lives of common people occupy straight
diagonal lines across the plane of time, sloping at a rate
of exactly one hour of time per hour of time2. The life
of the time traveler occupies a bent path, of varying
slope.
On closer inspection, however, this account seems not
to give us time travel as we know it from the stories.
When the traveler revisits the days of his childhood, will
his playmates be there to meet him? No; he has not
reached the part of the plane of time where they are. He
is no longer separated from them along one of the two
dimensions of time, but he is still separated from them
along the other. I do not say that two-dimensional time
is impossible, or that there is no way to square it with
the usual conception of what time travel would be like.
Nevertheless I shall say no more about two-dimensional
time. Let us set it aside, and see how time travel is possible
even in one-dimensional time.
The world—the time traveler’s world, or ours—is a
four-dimensional manifold of events. Time is one dimension
of the four, like the spatial dimensions except that
the prevailing laws of nature discriminate between time
and the others—or rather, perhaps, between various
timelike dimensions and various spacelike dimensions.
(Time remains one-dimensional, since no two timelike
dimensions are orthogonal.) Enduring things are timelike
streaks: wholes composed of temporal parts, or stages,
located at various times and places. Change is qualitative
difference between different stages—different temporal
parts—of some enduring thing, just as a “change” in
scenery from east to west is a qualitative difference between
the eastern and western spatial parts of the landscape.
If this paper should change your mind about the possibility of time travel, there will be a difference of
opinion between two different temporal parts of you, the
stage that started reading and the subsequent stage that
finishes.
If change is qualitative difference between temporal
parts of something, then what doesn’t have temporal
parts can’t change. For instance, numbers can’t change;
nor can the events of any moment of time, since they
cannot be subdivided into dissimilar temporal parts. (We
have set aside the case of two-dimensional time, and
hence the possibility that an event might be momentary
along one time dimension but divisible along the other.)
It is essential to distinguish change from “Cambridge
change,” which can befall anything. Even a number can
“change” from being to not being the rate of exchange
between pounds and dollars. Even a momentary event
can “change” from being a year ago to being a year and
a day ago, or from being forgotten to being remembered.
But these are not genuine changes. Not just any old reversal
in truth value of a time-sensitive sentence about
something makes a change in the thing itself.
A time traveler, like anyone else, is a streak through
the manifold of space-time, a whole composed of stages
located at various times and places. But he is not a streak
like other streaks. If he travels toward the past he is a
zig-zag streak, doubling back on himself. If he travels
toward the future, he is a stretched-out streak. And if he
travels either way instantaneously, so that there are no
intermediate stages between the stage that departs and
the stage that arrives and his journey has zero duration,
then he is a broken streak.
I asked how it could be that the same two events were
separated by two unequal amounts of time, and I set
aside the reply that time might have two independent
dimensions. Instead I reply by distinguishing time itself,
external time as I shall also call it, from the personal time
of a particular time traveler: roughly, that which is measured
by his wristwatch. His journey takes an hour of his
personal time, let us say; his wristwatch reads an hour
later at arrival than at departure. But the arrival is more
than an hour after the departure in external time, if he
travels toward the future; or the arrival is before the departure
in external time (or less than an hour after), if
he travels toward the past.
That is only rough. I do not wish to define personal
time operationally, making wristwatches infallible by
definition. That which is measured by my own wristwatch
often disagrees with external time, yet I am no
time traveler; what my misregulated wristwatch measures
is neither time itself nor my personal time. Instead
of an operational definition, we need a functional definition
of personal time; it is that which occupies a certain
role in the pattern of events that comprise the time traveler’s
life. If you take the stages of a common person,
they manifest certain regularities with respect to external
time. Properties change continuously as you go along,
for the most part, and in familiar ways. First come infantile
stages. Last come senile ones. Memories accumulate.
Food digests. Hair grows. Wristwatch hands move.
If you take the stages of a time traveler instead, they do
not manifest the common regularities with respect to external
time. But there is one way to assign coordinates
to the time traveler’s stages, and one way only (apart
from the arbitrary choice of a zero point), so that the
regularities that hold with respect to this assignment
match those that commonly hold with respect to external
time. With respect to the correct assignment properties
change continuously as you go along, for the most part,
and in familiar ways. First come infantile stages. Last
come senile ones. Memories accumulate. Food digests.
Hair grows. Wristwatch hands move. The assignment of
coordinates that yields this match is the time traveler’s
personal time. It isn’t really time, but it plays the role in
his life that time plays in the life of a common person.
It’s enough like time so that we can—with due caution—
transplant our temporal vocabulary to it in discussing
his affairs. We can say without contradiction, as the time
traveler prepares to set out, “Soon he will be in the past.”
We mean that a stage of him is slightly later in his personal
time, but much earlier in external time, than the
stage of him that is present as we say the sentence.
We may assign locations in the time traveler’s personal
time not only to his stages themselves but also to
the events that go on around him. Soon Caesar will die,
long ago; that is, a stage slightly later in the time traveler’s
personal time than his present stage, but long ago
in external time, is simultaneous with Caesar’s death.
We could even extend the assignment of personal time
to events that are not part of the time traveler’s life, and
not simultaneous with any of his stages. If his funeral in
ancient Egypt is separated from his death by three days
of external time and his death is separated from his birth
by three score years and ten of his personal time, then
we may add the two intervals and say that his funeral
follows his birth by three score years and ten and three
days of extended personal time. Likewise a bystander
might truly say, three years after the last departure of
another famous time traveler, that “he may even now—if
I may use the phrase—be wandering on some plesiosaurus-
haunted oolitic coral reef, or beside the lonely saline
seas of the Triassic Age.” If the time traveler does wander
on an oolitic coral reef three years after his departure
in his personal time, then it is no mistake to say with
respect to his extended personal time that the wandering
is taking place “even now”.
We may liken intervals of external time to distances
as the crow flies, and intervals of personal time to distances
along a winding path. The time traveler’s life is
like a mountain railway. The place two miles due east
of here may also be nine miles down the line, in the
westbound direction. Clearly we are not dealing here
with two independent dimensions. Just as distance along
the railway is not a fourth spatial dimension, so a time
traveler’s personal time is not a second dimension of time. How far down the line some place is depends on
its location in three-dimensional space, and likewise the
locations of events in personal time depend on their locations
in one-dimensional external time.
Five miles down the line from here is a place where
the line goes under a trestle; two miles further is a place
where the line goes over a trestle; these places are one
and the same. The trestle by which the line crosses over
itself has two different locations along the line, five miles
down from here and also seven. In the same way, an
event in a time traveler’s life may have more than one
location in his personal time. If he doubles back toward
the past, but not too far, he may be able to talk to himself.
The conversation involves two of his stages, separated
in his personal time but simultaneous in external time.
The location of the conversation in personal time should
be the location of the stage involved in it. But there are
two such stages; to share the locations of both, the conversation
must be assigned two different locations in personal
time.
The more we extend the assignment of personal time
outwards from the time traveler’s stages to the surrounding
events, the more will such events acquire multiple
locations. It may happen also, as we have already seen,
that events that are not simultaneous in external time
will be assigned the same location in personal time—or
rather, that at least one of the locations of one will be
the same as at least one of the locations of the other. So
extension must not be carried too far, lest the location of
events in extended personal time lose its utility as a
means of keeping track of their roles in the time traveler’s
history.
A time traveler who talks to himself, on the telephone
perhaps, looks for all the world like two different people
talking to each other. It isn’t quite right to say that the
whole of him is in two places at once, since neither of the
two stages involved in the conversation is the whole of
him, or even the whole of the part of him that is located
at the (external) time of the conversation. What’s true is
that he, unlike the rest of us, has two different complete
stages located at the same time at different places. What
reason have I, then, to regard him as one person and not
two? What unites his stages, including the simultaneous
ones, into a single person? The problem of personal identity
is especially acute if he is the sort of time traveler whose
journeys are instantaneous, a broken streak consisting of
several unconnected segments. Then the natural way to regard
him as more than one person is to take each segment
as a different person. No one of them is a time traveler,
and the peculiarity of the situation comes to this: all but
one of these several people vanish into thin air, all but another
one appear out of thin air, and there are remarkable
resemblances between one at his appearance and another
at his vanishing. Why isn’t that at least as good a description
as the one I gave, on which the several segments are
all parts of one time traveler?
I answer that what unites the stages (or segments) of
a time traveler is the same sort of mental, or mostly mental,
continuity and connectedness that unites anyone else.
The only difference is that whereas a common person is
connected and continuous with respect to external time,
the time traveler is connected and continuous only with
respect to his own personal time. Taking the stages in
order, mental (and bodily) change is mostly gradual
rather than sudden, and at no point is there sudden
change in too many different respects all at once. (We
can include position in external time among the respects
we keep track of, if we like. It may change discontinuously
with respect to personal time if not too much else
changes discontinuously along with it.) Moreover, there
is not too much change altogether. Plenty of traits and
traces last a lifetime. Finally, the connectedness and the
continuity are not accidental. They are explicable; and
further, they are explained by the fact that the properties
of each stage depend causally on those of the stages just
before in personal time, the dependence being such as
tends to keep things the same.
To see the purpose of my final requirement of causal
continuity, let us see how it excludes a case of counterfeit
time travel. Fred was created out of thin air, as if in the
midst of life; he lived a while, then died. He was created
by a demon, and the demon had chosen at random what
Fred was to be like at the moment of his creation. Much
later someone else, Sam, came to resemble Fred as he
was when first created. At the very moment when the
resemblance became perfect, the demon destroyed Sam.
Fred and Sam together are very much like a single person:
a time traveler whose personal time starts at Sam’s
birth, goes on to Sam’s destruction and Fred’s creation,
and goes on from there to Fred’s death. Taken in this
order, the stages of Fred-cum-Sam have the proper connectedness
and continuity. But they lack causal continuity,
so Fred-cum-Sam is not one person and not a time
traveler. Perhaps it was pure coincidence that Fred at his
creation and Sam at his destruction were exactly alike;
then the connectedness and continuity of Fred-cum-Sam
across the crucial point are accidental. Perhaps instead
the demon remembered what Fred was like, guided Sam
toward perfect resemblance, watched his progress, and
destroyed him at the right moment. Then the connectedness
and continuity of Fred-cum-Sam has a causal explanation,
but of the wrong sort. Either way, Fred’s first
stages do not depend causally for their properties on
Sam’s last stages. So the case of Fred and Sam is rightly
disqualified as a case of personal identity and as a case
of time travel.
We might expect that when a time traveler visits the
past there will be reversals of causation. You may punch
his face before he leaves, causing his eye to blacken centuries
ago. Indeed, travel into the past necessarily involves
reversed causation. For time travel requires
personal identity—he who arrives must be the same person
who departed. That requires causal continuity, in
which causation runs from earlier to later stages in the
order of personal time. But the orders of personal and
external time disagree at some point, and there we have
causation that runs from later to earlier stages in the order
of external time. Elsewhere I have given an analysis
of causation in terms of chains of counterfactual dependence,
and I took care that my analysis would not rule
out casual reversal a priori. I think I can argue (but not
here) that under my analysis the direction of counterfactual
dependence and causation is governed by the direction
of other de facto asymmetries of time. If so, then
reversed causation and time travel are not excluded altogether,
but can occur only where there are local exceptions
to these asymmetries. As I said at the outset, the
time traveler’s world would be a most strange one.
Stranger still, if there are local—but only local—causal
reversals, then there may also be causal loops: closed
causal chains in which some of the causal links are normal
in direction and others are reversed. (Perhaps there
must be loops if there is reversal: I am not sure.) Each
event on the loop has a causal explanation, being caused
by events elsewhere on the loop. That is not to say that
the loop as a whole is caused or explicable. It may not
be. Its inexplicability is especially remarkable if it is
made up of the sort of causal processes that transmit
information. Recall the time traveler who talked to himself.
He talked to himself about time travel, and in the
course of the conversation his older self told his younger
self how to build a time machine. That information was
available in no other way. His older self knew how because
his younger self had been told and the information
had been preserved by the causal processes that constitute
recording, storage, and retrieval of memory traces.
His younger self knew, after the conversation, because
his older self had known and the information had been
preserved by the causal processes that constitute telling.
But where did the information come from in the first
place? Why did the whole affair happen? There is simply
no answer. The parts of the loop are explicable, the whole
of it is not. Strange! But not impossible, and not too different
from inexplicabilities we are already inured to. Almost
everyone agrees that God, or the Big Bang, or the
entire infinite past of the universe, or the decay of a tritium
atom, is uncaused and inexplicable. Then if these
are possible, why not also the inexplicable causal loops
that arise in the time travel?
I have committed a circularity in order not to talk
about too much at once, and this is a good place to set
it right. In explaining personal time, I presupposed that
we were entitled to regard certain stages as comprising
a single person. Then in explaining what united the
stages into a single person, I presupposed that we were
given a personal time order for them. The proper way
to proceed is to define personhood and personal time
simultaneously, as follows. Suppose given a pair of an
aggregate of persona-stages, regarded as a candidate for
personhood, and an assignment of coordinates to those
stages, regarded as a candidate for his personal time. If
the stages satisfy the conditions given in my circular explanation
with respect to the assignment of coordinates,
then both candidates succeed: the stages do comprise a
person and the assignment is his personal time.
I have argued so far that what goes on in a time travel
story may be a possible pattern of events in four-dimensional
space-time with no extra time dimension; that it
may be correct to regard the scattered stages of the alleged
time traveler as comprising a single person; and
that we may legitimately assign to those stages and their
surroundings a personal time order that disagrees sometimes
with their order in external time. Some might concede
all this, but protest that the impossibility of time
travel is revealed after all when we ask not what the
time traveler does, but what he could do. Could a time
traveler change the past? It seems not: the events of a
past moment could no more change than numbers could.
Yet it seems that he would be as able as anyone to do
things that would change the past if he did them. If a
time traveler visiting the past both could and couldn’t
do something that would change it, then there cannot
possibly be such a time traveler.
Consider Tim. He detests his grandfather, whose success
in the munitions trade built the family fortune that
paid for Tim’s time machine. Tim would like nothing so
much as to kill Grandfather, but alas he is too late.
Grandfather died in his bed in 1957, while Tim was a
young boy. But when Tim has built his time machine and
traveled to 1920, suddenly he realizes that he is not too
late after all. He buys a rifle; he spends long hours in
target practice; he shadows Grandfather to learn the
route of his daily walk to the munitions works; he rents
a room along the route; and there he lurks, one winter
day in 1921, rifle loaded, hate in his heart, as Grandfather
walks closer, closer,. . . .
Tim can kill Grandfather. He has what it takes. Conditions
are perfect in every way: the best rifle money
could buy, Grandfather an easy target only twenty yards
away, not a breeze, door securely locked against intruders.
Tim a good shot to begin with and now at the peak
of training, and so on. What’s to stop him? The forces
of logic will not stay his hand! No powerful chaperone
stands by to defend the past from interference. (To imagine
such a chaperone, as some authors do, is a boring
evasion, not needed to make Tim’s story consistent.) In
short, Tim is as much able to kill Grandfather as anyone
ever is to kill anyone. Suppose that down the street another
sniper, Tom, lurks waiting for another victim,
Grandfather’s partner. Tom is not a time traveler, but otherwise
he is just like Tim: same make of rifle, same murderous
intent, same everything. We can even suppose
that Tom, like Tim, believes himself to be a time traveler.
Someone has gone to a lot of trouble to deceive Tom into
thinking so. There’s no doubt that Tom can kill his victim;
and Tim has everything going for him that Tom
does. By any ordinary standards of ability, Tim can kill
Grandfather.
Tim cannot kill Grandfather. Grandfather lived, so to kill
him would be to change the past. But the events of a past
moment are not subdivisible into temporal parts and therefore
cannot change. Either the events of 1921 timelessly
do include Tim’s killing of Grandfather, or else they
timelessly don’t. We may be tempted to speak of the
“original” 1921 that lies in Tim’s personal past, many
years before his birth, in which Grandfather lived; and
of the “new” 1921 in which Tim now finds himself waiting
in ambush to kill Grandfather. But if we do speak
so, we merely confer two names on one thing. The events
of 1921 are doubly located in Tim’s (extended) personal
time, like the trestle on the railway, but the “original” 1921
and the “new” 1921 are one and the same. If Tim did not
kill Grandfather in the “original” 1921, then if he does kill
Grandfather in the “new” 1921, he must both kill and not
kill Grandfather in 1921—in the one and only 1921, which
is both the “new” and the “original” 1921. It is logically
impossible that Tim should change the past by killing
Grandfather in 1921. So Tim cannot kill Grandfather.
Not that past moments are special; no more can anyone
change the present or the future. Present and future
momentary events no more have temporal parts than
past ones do. You cannot change a present or future
event from what it was originally to what it is after you
change it. What you can do is to change the present or
the future from the unactualized way they would have
been without some action of yours to the way they actually
are. But that is not an actual change: not a difference
between two successive actualities. And Tim can
certainly do as much; he changes the past from the unactualized
way it would have been without him to the
one and only way it actually is. To “change” the past in
this way, Tim need not do anything momentous; it is
enough just to be there, however unobtrusively.
You know, of course, roughly how the story of Tim
must go on if it is to be consistent: he somehow fails.
Since Tim didn’t kill Grandfather in the “original” 1921,
consistency demands that neither does he kill Grandfather
in the “new” 1921. Why not? For some commonplace
reason. Perhaps some noise distracts him at the last
moment, perhaps he misses despite all his target practice,
perhaps his nerve fails, perhaps he even feels a pang of
unaccustomed mercy. His failure by no means proves
that he was not really able to kill Grandfather. We often
try and fail to do what we are able to do. Success at
some tasks requires not only ability but also luck, and
lack of luck is not a temporary lack of ability. Suppose
our other sniper, Tom, fails to kill Grandfather’s partner
for the same reason, whatever it is, that Tim fails to kill
Grandfather. It does not follow that Tom was unable to.
No more does it follow in Tim’s case that he was unable
to do what he did not succeed in doing.
We have this seeming contradiction: “Tim doesn’t, but
can, because he has what it takes” versus “Tim doesn’t, and
can’t, because it’s logically impossible to change the past.” I
reply that there is no contradiction. Both conclusions are
true, and for the reasons given. They are compatible because
“can” is equivocal.
To say that something can happen means that its happening
is compossible with certain facts. Which facts?
That is determined, but sometimes not determined well
enough, by context. An ape can’t speak a human language—
say, Finnish—but I can. Facts about the anatomy
and operation of the ape’s larynx and nervous system
are not compossible with his speaking Finnish. The corresponding
facts about my larynx and nervous system
are compossible with my speaking Finnish. But don’t
take me along to Helsinki as your interpreter: I can’t
speak Finnish. My speaking Finnish is compossible with
the facts considered so far, but not with further facts
about my lack of training. What I can do, relative to one
set of facts, I cannot do, relative to another, more inclusive,
set. Whenever the context leaves it open which facts
are to count as relevant, it is possible to equivocate about
whether I can speak Finnish. It is likewise possible to
equivocate about whether it is possible for me to speak
Finnish, or whether I am able to, or whether I have the
ability or capacity or power or potentiality to. Our many
words for much the same thing are little help since they
do not seem to correspond to different fixed delineations
of the relevant facts.
Tim’s killing Grandfather that day in 1921 is compossible
with a fairly rich set of facts: the facts about his
rifle, his skill and training, the unobstructed line of fire,
the locked door and the absence of any chaperone to
defend the past, and so on. Indeed it is compossible with
all the facts of the sorts we would ordinarily count as
relevant is saying what someone can do. It is compossible
with all the facts corresponding to those we deem
relevant in Tom’s case. Relative to these facts, Tim can
kill Grandfather. But his killing Grandfather is not compossible
with another, more inclusive set of facts. There
is the simple fact that Grandfather was not killed. Also
there are various other facts about Grandfather’s doings
after 1921 and their effects: Grandfather begat Father in
1922 and Father begat Tim in 1949. Relative to these facts,
Tim cannot kill Grandfather. He can and he can’t, but
under different delineations of the relevant facts. You
can reasonably choose the narrower delineation, and
say that he can; or the wider delineation, and say that
he can’t. But choose. What you mustn’t do is waver,
say in the same breath that he both can and can’t, and
then claim that this contradiction proves that time
travel is impossible.
Exactly the same goes for Tom’s parallel failure. For
Tom to kill Grandfather’s partner also is compossible
with all facts of the sorts we ordinarily count as relevant,
but not compossible with a larger set including, for instance,
the fact that the intended victim lived until 1934.
In Tom’s case we are not puzzled. We say without hesitation
that he can do it, because we see at once that the
facts that are not compossible with his success are facts
about the future of the time in question and therefore
not the sort of facts we count as relevant in saying what
Tom can do.
In Tim’s case it is harder to keep track of which facts
are relevant. We are accustomed to exclude facts about
the future of the time in question, but to include some
facts about its past. Our standards do not apply unequivocally
to the crucial facts in this special case: Tim’s
failure, Grandfather’s survival, and his subsequent doings.
If we have foremost in mind that they lie in the
external future of that moment in 1921 when Tim is almost
ready to shoot, then we exclude them just as we
exclude the parallel facts in Tom’s case. But if we have
foremost in mind that they precede that moment in Tim’s
extended personal time, then we tend to include them.
To make the latter be foremost in your mind, I chose to
tell Tim’s story in the order of his personal time, rather
than in the order of external time. The fact of Grandfather’s
survival until 1957 had already been told before I
got to the part of the story about Tim lurking in ambush
to kill him in 1921. We must decide, if we can, whether
to treat these personally past and externally future facts
as if they were straightforwardly past or as if they were
straightforwardly future.
Fatalists—the best of them—are philosophers who
take facts we count as irrelevant in saying what someone
can do, disguise them somehow as facts of a different
sort that we count as relevant, and thereby argue that
we can do less than we think—indeed, that there is nothing
at all that we don’t do but can. I am not going to
vote Republican next fall. The fatalist argues that, strange
to say, I not only won’t but can’t; for my voting Republican
is not compossible with the fact that it was true
already in the year 1548 that I was not going to vote
Republican 428 years later. My rejoinder is that this is
a fact, sure enough; however, it is an irrelevant fact
about the future masquerading as a relevant fact about
the past, and so should be left out of account in saying
what, in any ordinary sense, I can do. We are unlikely
to be fooled by the fatalist’s methods of disguise in
this case, or other ordinary cases. But in cases of time
travel, precognition, or the like, we’re on less familiar
ground, so it may take less of a disguise to fool us.
Also, new methods of disguise are available, thanks to
the device of personal time.
Here’s another bit of fatalist trickery. Tim, as he lurks,
already knows that he will fail. At least he has the wherewithal
to know it if he thinks, he knows it implicitly. For
he remembers that Grandfather was alive when he was
a boy, he knows that those who are killed are thereafter
not alive, he knows (let us suppose) that he is a time
traveler who has reached the same 1921 that lies in his
personal past, and he ought to understand—as we do—
why a time traveler cannot change the past. What is
known cannot be false. So his success is not only not
compossible with facts that belong to the external future
and his personal past, but also is not compossible with
the present fact of his knowledge that he will fail. I
reply that the fact of his foreknowledge, at the moment
while he waits to shoot, is not a fact entirely about that
moment. It may be divided into two parts. There is the fact
that he then believes (perhaps only implicitly) that he will
fail; and there is the further fact that his belief is correct,
and correct not at all by accident, and hence qualifies as
an item of knowledge. It is only the latter fact that is not
compossible with his success, but it is only the former
that is entirely about the moment in question. In calling
Tim’s state at that moment knowledge, not just belief,
facts about personally earlier but externally later moments
were smuggled into consideration.
I have argued that Tim’s case and Tom’s are alike, except
that in Tim’s case we are more tempted than usual—
and with reason—to opt for a semi-fatalist mode of
speech. But perhaps they differ in another way. In Tom’s
case, we can expect a perfectly consistent answer to the
counterfactual question: what if Tom had killed Grandfather’s
partner? Tim’s case is more difficult. If Tim had
killed Grandfather, it seems offhand that contradictions
would have been true. The killing both would and
wouldn’t have occurred. No Grandfather, no Father; no
Father, no Tim; no Tim, no killing. And for good measure:
no Grandfather, no family fortune; no fortune, no time
machine; no time machine, no killing. So the supposition
that Tim killed Grandfather seems impossible in more
than the semi-fatalistic sense already granted.
If you suppose Tim to kill Grandfather and hold all
the rest of his story fixed, of course you get a contradiction.
But likewise if you suppose Tom to kill Grandfather’s
partner and hold the rest of his story
fixed—including the part that told of his failure—you
get a contradiction. If you make any counterfactual supposition
and hold all else fixed you get a contradiction.
The thing to do is rather to make the counterfactual supposition
and hold all else as close to fixed as you consistently
can. That procedure will yield perfectly
consistent answers to the question: what if Tim had not
killed Grandfather? In that case, some of the story I told
would not have been true. Perhaps Tim might have been
the time-traveling grandson of someone else. Perhaps he
might have been the grandson of a man killed in 1921
and miraculously resurrected. Perhaps he might have
been not a time traveler at all, but rather someone created
out of nothing in 1920 equipped with false memories
of a personal past that never was. It is hard to say
what is the least revision of Tim’s story to make it true
that Tim kills Grandfather, but certainly the contradictory
story in which the killing both does and doesn’t occur
is not the least revision. Hence it is false (according to
the unrevised story) that if Tim had killed Grandfather
then contradictions would have been true.
What difference would it make if Tim travels in
branching time? Suppose that at the possible world of
Tim’s story the space-time manifold branches; the
branches are separated not in time, and not in space, but
in some other way. Tim travels not only in time but also
from one branch to another. In one branch Tim is absent
from the events of 1921; Grandfather lives; Tim is born,
grows up, and vanishes in his time machine. The other
branch diverges from the first when Tim turns up in
1920; there Tim kills Grandfather and Grandfather leaves
no descendants and no fortune; the events of the two
branches differ more and more from that time on. Certainly
this is a consistent story; it is a story in which
Grandfather both is and isn’t killed in 1921 (in the different
branches); and it is a story in which Tim, by killing
Grandfather, succeeds in preventing his own birth (in
one of the branches). But it is not a story in which Tim’s
killing of Grandfather both does occur and doesn’t: it
simply does, though it is located in one branch and not
the other. And it is not a story in which Tim changes the
past. 1921 and later years contain the events of both
branches, coexisting somehow without interaction. It remains
true at all the personal times of Tim’s life, even
after the killing, that Grandfather lives in one branch and
dies in the other.

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Is time travel possible?

Members of the Tripoli Minnesota Rocket Club #45 ask a very intriguing question this month: Is time travel possible?
Time travel is one of my favorite topics! I wrote some time travel stories in junior high school that used a machine of my own invention to travel backwards in time, and I have continued to study this fascinating concept as the years have gone by.
We all travel in time. During the last year, I've moved forward one year and so have you. Another way to say that is that we travel in time at the rate of 1 hour per hour.
But the question is, can we travel in time faster or slower than "1 hour per hour"? Or can we actually travel backward in time, going back, say 2 hours per hour, or 10 or 100 years per hour?
It is mind-boggling to think about time travel. What if you went back in time and prevented your father and mother from meeting? You would prevent yourself from ever having been born! But then if you hadn't been born, you could not have gone back in time to prevent them from meeting.
The great 20th century scientist Albert Einstein developed a theory called Special Relativity. The ideas of Special Relativity are very hard to imagine because they aren't about what we experience in everyday life, but scientists have confirmed them. This theory says that space and time are really aspects of the same thing—space-time. There's a speed limit of 300,000 kilometers per second (or 186,000 miles per second) for anything that travels through space-time, and light always travels the speed limit through empty space.
Special Relativity also says that a surprising thing happens when you move through space-time, especially when your speed relative to other objects is close to the speed of light. Time goes slower for you than for the people you left behind. You won't notice this effect until you return to those stationary people.
Say you were 15 years old when you left Earth in a spacecraft traveling at about 99.5% of the speed of light (which is much faster than we can achieve now), and celebrated only five birthdays during your space voyage. When you get home at the age of 20, you would find that all your classmates were 65 years old, retired, and enjoying their grandchildren! Because time passed more slowly for you, you will have experienced only five years of life, while your classmates will have experienced a full 50 years.

So, if your journey began in 2003, it would have taken you only 5 years to travel to the year 2053, whereas it would have taken all of your friends 50 years. In a sense, this means you have been time traveling. This is a way of going to the future at a rate faster than 1 hour per hour.
Time travel of a sort also occurs for objects in gravitational fields. Einstein had another remarkable theory called General Relativity, which predicts that time passes more slowly for objects in gravitational fields (like here on Earth) than for objects far from such fields. So there are all kinds of space and time distortions near black holes, where the gravity can be very intense.
In the past few years, some scientists have used those distortions in space-time to think of possible ways time machines could work. Some like the idea of "worm holes," which may be shortcuts through space-time. This and other ideas are wonderfully interesting, but we don't know at this point whether they are possible for real objects. Still the ideas are based on good, solid science. In all time travel theories allowed by real science, there is no way a traveler can go back in time to before the time machine was built.
I am confident time travel into the future is possible, but we would need to develop some very advanced technology to do it. We could travel 10,000 years into the future and age only 1 year during that journey. However, such a trip would consume an extraordinary amount of energy. Time travel to the past is more difficult. We do not understand the science as well.
Actually, scientists and engineers who plan and operate some space missions must account for the time distortions that occur because of both General and Special Relativity. These effects are far too small to matter in most human terms or even over a human lifetime. However, very tiny fractions of a second do matter for the precise work necessary to fly spacecraft throughout the solar system.
Find out how one NASA mission is doing some very clever space-time experiments to test Einstein's theory of relativity using the International Space Station.

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NASA's The Space Place

If you built a Newtonian Physics Machine, you have seen how we can discover laws of nature we see working every day. Humans understand these laws, first described by Isaac Newton 300 years ago. Now scientists have new tools to help them study how these well-known laws affect nature on the smallest and largest scales. And they also have new tools to discover laws of nature no one knows about yet.
NASA's "Fundamental Physics in Space" program uses the special "microgravity" conditions of space to test out new ideas about the laws of nature.
Scientists working on these questions are doing some very strange things! In one set of experiments, they will be testing the most accurate clocks ever made.
Like the moving balls of your Newtonian Physics Machine, the atoms and molecules that make up all matter are moving constantly. The faster the atoms in a material are moving, the hotter it is.
Scientists have found a way to super-cool atoms by slowing them down using laser beams. Lasers are a particular kind of "well-organized" light. The light acts kind of like very fast moving particles with . . . you guessed it . . . momentum! The light particles slow down the atoms that come at them from the opposite direction. If the lasers are pointing toward the same spot from several different directions, the atoms can't go much of anywhere.
Once the atoms are moving very slowly, it is much easier to use another kind of light, called microwaves, to measure the time it takes for the atom to go from one state to another. This time is so tiny, yet so constant, that if we can learn to measure it, we will be able to make clocks that are accurate to .000000000000001, or one-quadrillionth of a second!
For a couple of reasons, these experiments need to be done in space. They will be done on the International Space Station. In orbit around Earth, the Space Station and everything in it are in free fall, so the atoms in the experiments will not be disturbed by the effects of gravity. Also, the pull of Earth's gravity really is less the farther from Earth one goes. As you will see, this fact is an important part of these experiments.

The Primary Atomic Reference Clock in Space (PARCS) experiment will put an advanced atomic clock on the International Space Station. This laser-cooled clock will be used to test a prediction of Einstein's Theory of Relativity. This prediction says that clocks tick slower in strong gravity than they do in weak gravity. The Space Station orbits at an altitude of 360 kilometers (220 miles), where gravity is slightly weaker than on Earth's surface. (Remember, the astronauts feel weightless only because they are in free fall.) If Einstein's theory is correct, a clock aboard the Space Station should tick faster than a clock on the surface of the Earth by about 1 second in every 10,000 years. It will take a very accurate clock to measure this tiny change!

The Rubidium Atomic Clock Experiment (RACE) will build on the PARCS experiment to make an even more accurate clock. This clock will keep time so well that if it ran for three billion years it would lose less than 1 second! Future clocks based on the technology developed for RACE might be used to coordinate all of the world's clocks, as well as for telecommunications, and navigation—both on Earth and in space.

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Learning the rules . . .

"We can imagine that this complicated array of moving things which constitute 'the world' is something like a great chess game being played by the gods, and we are observers of the game. We do not know what the rules of the game are; all we are allowed to do is to watch the playing. Of course, if we watch long enough, we may eventually catch on to a few of the rules. The rules of the game are what we mean by fundamental physics.

- " Richard Feynman

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Wormholes as Time Machines

You’ve chosen to use them clicking on this article, rather than pursuing hang gliding, water skiing, mountain climbing, chocolate sampling, or countless other options. Sure you could do those things later, but what was “now” is already gone. If only you had a wormhole time machine and could go back in time to undo your choice! But how to make a wormhole time machine? Read on if you’d like some suggestions from the world of theoretical physics.

Step in to my time machine. Credit: NASA/Les Bossinas (Cortez III Service Corp.),

 Flash back to the late 1980s—with your imagination, not a time machine just yet. The extraordinary astronomer and science communicator Carl Sagan, fresh off his award-winning PBS series Cosmos, decided to write a science fiction novel about interstellar travel, "Contact." Needing a way for his protagonist to travel quickly to another planet, he asked his friend Caltech astrophysicist Kip Thorne for advice.

Thorne is an expert in general relativity, Einstein’s masterful theory of gravity. The equations of general relativity serve as a recipe for how nature kneads the dough of spacetime (space and time combined) into various shapes—from as flat as a pancake to as curvy as a croissant. These shapes determine how other things move. Just as an ant at a picnic would take a more winding route around an apple than across a napkin, objects in the universe (planets, comets, and so forth) veer along curved paths in warped regions. What distorts these sectors of spacetime is the amount and distribution of mass and energy. For example, the gravitational well of the solar system is carved out by the mass of the Sun.

In extreme cases, a glop of mass concentrated in a small enough region will tear the fabric of spacetime, causing what is called a singularity—a point of infinite density where spacetime seems to reach a dead end. Such is the case with what is called the Schwarzschild solution of Einstein’s equations of general relativity, used to describe the ultra-dense, collapsed stellar cores known as black holes. However, as Einstein and his assistant Nathan Rosen showed in 1935, one can mathematically extend the Schwarzschild solution across an “Einstein-Rosen bridge” and link it to another region of spacetime. In the 1960s, the creative Princeton physicist John Wheeler, who was Thorne’s PhD advisor, dubbed these connections “wormholes,” imagining a worm taking a shortcut by crossing an apple’s interior. (Wheeler also coined the term “black hole.”)

When Sagan contacted Thorne he was envisioning something like a Schwarzschild wormhole connecting two otherwise distant parts of space—an interstellar Chunnel, so to speak. But Thorne realized that a Schwarzschild wormhole wouldn’t do. For one thing, it was unstable to matter, meaning that the gravitational effect of even the slightest drop of mass would cause it to collapse. Therefore it would close off if a spaceship tried to enter—that is, if the space voyagers could make it that far. If the wormhole entrance lay in the bowels of a black hole, the travelers would encounter deadly radiation, bone-crushing gravitational forces, and enough stomach-churning acceleration to make even the Dangerous Sports Club give it a miss.

Thorne asked his then-student Michael Morris to help him come up with an alternative. They crafted a novel solution of Einstein’s equations of general relativity that would represent a wormhole that could be traversable by human voyagers, such as the fictional heroine of "Contact." The solution was custom-designed to eliminate the nasty aspects of navigating into a black hole and allow for a relatively quick, comfortable ride. After passing into the wormhole’s “mouth” (as its entrance was called) and journeying through its “throat” (as its passageway was called), a voyager would find herself emerging from another mouth somewhere in another part of space. Instead of traveling hundreds of years or more to reach another star, if all went well, she’d swiftly arrive in its vicinity.

Morris and Thorne realized that their scheme was extremely hypothetical—requiring a virtually inconceivable engineering feat. For one thing, the amount of mass needed to create the wormhole was comparable to that of a galaxy. Moreover, a new type of negative mass material, called “exotic matter,” would be necessary to prop open the wormhole’s throat and prevent it from collapsing. No known substance has negative mass.

Offering some cause for optimism, physicist Matt Visser of Victoria University of Wellington soon found a way to minimize the amount of exotic matter required. As he and others have pointed out, exotic matter has features in common with the energy of the quantum vacuum, the bedrock state of particle physics, which has a repulsive pressure. Perhaps a future civilization could mine enough of this energy to suffice for wormhole construction. A hypothetical energy called “phantom energy,” a type of dark energy with a considerable amount of negative pressure, used to explain the acceleration of the universe’s expansion, also holds promise as a potential way to stabilize wormholes.

Shortly after Morris and Thorne published their first paper they collaborated with Ulvi Yurtsever, another of Thorne’s PhD students at Caltech, on another remarkable article showing how a wormhole could be used as a time machine. The key would be to speed up one of the mouths of the wormhole to close to the speed of light while leaving the other one fixed. According to the phenomenon of time dilation, an aspect of Einstein’s special theory of relativity, time in the vicinity of a near-light-speed object will slow down significantly relative to a stationary observer. Therefore, while the fixed mouth ages 100 years, the high-speed mouth, if it is fast enough, might experience only one year. If the calendar reads 2112 for the former, it would read 2013 for the latter. Now suppose a space traveler sails into the fixed mouth in 2112. If passage through the throat is quick enough, she would emerge through the moving mouth in 2013.

If you are still thinking about all the things you could have done if you hadn’t clicked on this post, you now know the answer. Assuming you have an advanced spaceship and a CPS device (Cosmic Positioning System), simply find a wormhole, journey through it, go back to the time before you started reading this, and convince yourself to go surfing instead. You are cautioned however that your actions would create a paradox1, because if you never read the article you wouldn’t know how to go back in time (or at least wouldn’t have the need). Proceed to the past at your own risk!

1 To avoid paradoxes such as meeting yourself in the past and convincing yourself never to pursue time travel, or going back in time and accidently eliminating your ancestors, some physicists have asserted that backward time travel is impossible. Stephen Hawking, for example, postulated the Chronology Protection Conjecture to shield the past from tampering. Others such as Igor Novikov of Moscow State University and the Lebedev Physics Institute in Russia have argued, in what he called the Self-Consistency Principle, that past-directed temporal voyages are fine as long as the altered past is consistent with the present—that is, it was really supposed to happen. For example, if you go back in time and convince Carl Sagan that wormholes wouldn’t fit into his novel, maybe that’s just the incentive he needed to contact Kip Thorne and check if they would, leading to what actually happened. Finally, there are some who speculate that backward time travel could lead to a bifurcation of time into parallel realities.

In any case, the work of Thorne, Morris, Yurtsever, Novikov, Hawking, Visser and others has propelled the discussion of time travel and wormholes from fanciful science fiction into serious, peer-reviewed—albeit highly speculative—science. Who knows, perhaps someday our civilization will be advanced enough to test such far-reaching hypotheses and create or find actual wormholes. Only time will tell—and if wormholes exist, we have all the time in the world.

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Wormhole physics

Wormhole physics is the science behind the knowledge of wormholes. Known people within this profession are Colonel Samantha Carter, Dr. Rodney McKay, Dr. Peter Grodin and Dr. Nicholas Rush. As part of wormhole physics, there is also a branch regarding solely the Stargates who work on the principle with wormholes. Samantha Carter is considered the leading expert on Stargate wormhole physics and once wrote a book on the topic. (SG1: "Upgrades")
Laws of wormhole physics

Note that many of these laws relate specifically to wormholes created by Ancient Stargates and may not apply to natural wormholes or those created through other technologies (assuming other technologies for creating wormholes exist).

    The power required to activate and maintain a wormhole in the Stargate is literally astronomical.

    Artificial wormholes cannot be sustained for more than 38 minutes under normal conditions. Massive amounts of power can bypass this rule.

    The speed at which one enters a wormhole is the same at which one exits a wormhole. However unstable energy sources can cause travelers to exit at far greater velocities then they enter.

    The energy to maintain a wormhole can come from either end but the energy to dial in must come from the dialing gate.

    Matter and energy can travel both ways through an open wormhole, but as a limitation of the Stargates, the matter deconstruction/reconstruction event horizons can only transmit matter in one direction (outgoing) per dialing.

    Substantial gravitational force can pass through a wormhole from either side. (e.g., the effects of a black hole).

    Outgoing wormholes can be affected by exterior gravitational and electromagnetic forces, causing them to connect to Stargates other than their intended targets.

    Wormholes can be affected by Solar flares, causing them to pass back along themselves taking the traveler through time.

    The diameter of a Stargate is not arbitrary in regards to energy needed for a wormhole. A Supergate requires more energy than a regular Stargate indicating that the larger the event horizon, the more energy required.

    Radio signals cannot reach across a 9th chevron connection.

Out-of-Universe Wormholes

While wormholes are quite obviously possible in the Stargate franchise (and share several properties with 'real' wormholes), real-world science has only been able to theorize on their possible existence. Like the wormholes depicted in Stargate, 'real' wormholes are theorized to require vast amounts of energy to maintain; as a result, a wormhole would have to be subatomically small to exist for more than a fraction of a second in normal space.

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How EINSTEIN Arrived at E=MC2

 

Dear Friends:

Most people think Einstein was a genius. Even though he did poorly in school, it is generally assumed that Einstein became a genius later on. It's also widely believed that he used superior intellect and complex mathematical reasoning to finally arrive at E=MC2.

The truth about Einstein is altogether different. Even though he was pretty smart, his accomplishments didn't come from a wildly superior intellect. He didn't arrive at his famous equation by complex mathematical reasoning. In fact, he didn't use mathematical or scientific reasoning at all!
If Einstein didn't arrive at E=MC2 by mathematical or scientific reasoning, how did he get there? The answer is very simple...

 

He made it up!

That's right. He took a wild stab. He guessed. He made it all up! Without any proof, evidence, or scientific reasoning, he just woke up one day and said "It's got to be so." Then, in 1905, he published his "discovery" in a three-paged article in an obscure scientific journal and...well, the rest is history.

Here's what really happened.

Einstein wasn't as big a genius as most people think. He did have a curious mind, however, and he wasn't afraid to think differently than other people around him believed.

Around the time Einstein became interested in physics (1895), electricity, magnetism, and the phenomenon of light were all under intensive study. A number of scientific theories and mathematical equations had already been worked out. There was even a type of relativity theory in existence, called the relativity principle, which had been formulated centuries earlier by the astronomer Galileo.

Most scientists at the time were completely satisfied with these prevailing theories. There were a few situations these theories couldn't satisfactorily explain, but these exceptions were considered insignificant and no one really paid much attention to them.

 No one, except Einstein, that is.

Einstein was intrigued by these "holes" in the prevailing theories. In fact, he enjoyed posing "mind riddles" to himself, just to see if present theories could satisfactorily explain them.

One such riddle he posed to himself was this: If a person was flying in space at the speed of light (ala Superman) with his/her arm fully outstretched holding a facial mirror, what would they "see" in the mirror? Would they see their face? Would it be bigger or smaller than if they were stationary? Would it be distorted in any way? Would light waves have time to bounce off their face, hit the mirror, and bounce back to their retina which was also moving at the speed of light? And what if an observer was watching all this from the ground. What would he or she see?

This was the riddle that eventually led Einstein to E=MC2. As you can see, it's nothing exceptional. You or I could have easily wondered the same thing.

What made Einstein different, however, is that he refused to give up until he solved the riddle. He didn't stay with this riddle for just a week or two, as you or I might have done. He didn't give up after a month went by without an answer. He didn't even quit after a year or two of racking his brain.

He stuck with the riddle until he figured it out. He stuck with this riddle for...

 

Ten full years!

That's right...ten years, from 1895-1905! He pondered this riddle almost every day. He discussed it with his friends. He explored it with his colleagues. He even discussed it with the greatest scientific minds of his time. No one could come up with the answer.

But the great thing about Einstein was that he didn't give in like most people would have done. He didn't say "that's enough time spent on that one...let me go on to bigger and better things." No, he stayed with the question he originally posed. He resisted the temptation to accept an incomplete answer...any answer...just to bring the process to a close. He maintained his integrity and curiosity throughout. And when the answer finally came, he knew it was correct.

How did Einstein finally solve this riddle? Well, as I've already mentioned, he took a wild guess. After years and years of struggling with this problem, he finally had an insight that changed the course of modern civilization. What was this insight? Actually, it wasn't all that complex. And it didn't take a genius to think of it.
All Einstein did was to assume that the speed of light was constant! He assumed that nothing could go faster than the speed of light, and that all light traveled at the same basic speed, regardless of the observer.

Up to this time, it had not been established that the speed of light was constant. Everyone thought that time and distance were constants, but that the speed of light, like the speed of everything else in the universe, was variable. But Einstein was willing to consider that what everyone believed about light, time, and distance might actually be wrong!

So he took this assumption--that the speed of light was a constant--and he returned to the mathematical and electromagnetic equations that were worked out years before. He then plugged in the letter "C" (a constant) to represent the fixed speed of light (whatever it might be) and low and behold...

 

Out Popped E=MC2 !!

Einstein was astounded! If the speed of light was truly a constant--as he had intuitively guessed--then energy and matter must be one and the same (energy equals matter times the speed of light squared). Not only must energy and matter be the same, but the amount of energy in even the tiniest piece of matter, like the head of a pencil, is phenomenal--far exceeding any conventional bomb or explosive!

Not only that! If the speed of light were constant, Einstein also reasoned that time and distance must therefore be relative! But this was totally contrary to what everyone, including the world's leading scientists, believed.

This didn't stop Einstein, however. In 1905, he published his argument, including his conclusion that E=MC2, in a three-page paper entitled "Does The Inertia Of A Body Depend On It's Energy Content?" The paper had no footnotes and not one single reference to support it.

 The scientific establishment went absolutely bonkers.

"Who does this Einstein think he is? How dare he contradict the fundamental principles of Newtonian physics. Where is his scientific evidence? What are his credentials for making such an assertion? This is preposterous....we can't allow people just to say things like this without proof! How dare he...this idea should be given no credence at all!"

What was Einstein's response? How did he deal with all the negative criticism coming his way? His response was simple and direct. Basically, he told the scientific community...

 

Check it out--you'll see that it's true!

As it turned out, Einstein was right. Twenty years later, when the technology became available to put Einstein's assumption to a rigorous scientific test, his theory was validated. Eventually, the whole world had to agree that Einstein's original "hunch" was correct. The truth (at least as far as we know it today) eventually won out, although it took a long, long time before it was fully embraced.

 Why am I telling you this story? Why should you care how Einstein arrived at E=MC2?

I admire this story not because it relates to the science of physics, but because it relates very directly to you and me. It relates to who we are as human beings. It relates to our own capacities to think, reason, and understand how life really works. It even relates to how much stress we experience.

Knowing how Einstein arrived at E=MC2 helps us appreciate that we are all capable of achieving similar breakthroughs. Each of us is capable of waking up one day and realizing that:

1. The truth about life may not be what we've been told;
2. The truth about life may be very different than what most learned people believe;
3. We don't always need proof, evidence, or the agreement of others to embrace a new "truth" if we have good reason to believe in it's utility.

Look back over your own life for a moment.

Aren't there times when you saw some truth other people couldn't see or refused to acknowledge? Weren't there moments when everyone around you all thought or felt the same way, but you had the courage to see things differently...and you were eventually proven right?

Bet you didn't know you had some Einstein in you!

The amazing thing about Einstein wasn't so much his intellect--it was his COURAGE. Not only did he dare to question "gospel truths" that everyone around believed in very strongly, but he also had the courage to stick to his guns when everyone around him started attacking him intensely.

He was confident in his assessments. He stood firm in the face of expanding criticism, because he was clear he was on to something "real" and important. And no matter how strongly people disagreed with him, he maintained his integrity and didn't cave in.

Of course, Einstein wasn't the only person to demonstrate such a remarkable mix of insight and courage. Galileo and Copernicus also met with initial disapproval. So did Columbus, Thomas Edison, and Martin Luther King.

But the important point to remember is that we too are capable of the same type of heroic discoveries. We too can wake up any day and say to ourselves "you know, everything I thought I knew about `X' could be wrong!" And then either on our own, or with the help of others, we could explore this possibility with the same type of courage and conviction that Einstein brought to his ten-year riddle.

In my own life, I've achieved many such Einstein-like breakthroughs.

I remember the moment when, as a psychotherapy patient, I first discovered that I actually had an unconscious! There it was...clear as day...a powerful presence inside me that was capable of doing some pretty amazing things (and some pretty obnoxious things as well). I had never seen this part of me before.
I had no idea anything other than my rational "mind" was operating inside me. Then one day my whole understanding of myself--and other people--changed dramatically! And you know what?...

 

I've never gone back to my old way of thinking!

It's been over 20 years now that I made this remarkable discovery, thanks to the help of very good therapist. Ever since then, I've been able to recognize my "unconscious mind" wherever I go. It's never gone away. That's because it is truly there. It's a "truth" about me, about reality, about people in general, and about how the world really works. The only problem was that I was never able to "see" this truth before. And most other people around me couldn't see it either. Yet it was there all along!

I know some of you may not be able to relate to this example. Fortunately, we don't have to limit ourselves to huge, momentous, life-changing breakthroughs. We can have Einstein-like breakthroughs in mundane areas of life as well.

 Take the game of backgammon for example.

Whether you know how to play backgammon or not, almost everyone has at seen the game being played. At the very least, almost everyone has said to themselves at one time or another "I wonder what all those funny looking triangular black and red spaces on the flip side of my checker board are for?" (They're for playing backgammon.)

Anyhow, when I first started playing backgammon years ago, I thought it was a pretty stupid game. It really didn't require much skill. You roll the dice, move your pieces, and whoever gets lucky and rolls the highest numbers without getting "hit" wins. Nothing to get real excited about, right?

Well, I started playing backgammon for money with some of the tennis pros at my local racquet club. I was beaten consistently...five out of six times...eight out of ten times. Not only was this personally humiliating...it was costing me a fortune!

If backgammon was a game of pure chance, as I believed, I should have won about 50% of the time. Something very strange and "unnatural" therefore was clearly going on. Then, one day, one of the tennis pros who'd been gobbling up my money finally felt sorry for me. He took me aside and said, "why don't you go to the library and check out some books on backgammon and read them."

I was just as astounded as Einstein must have been when he hit upon E=MC2. "You mean people have actually written books about backgammon?" I said. Well I took his advice and checked it out. Yes, there were books in the library on backgammon. I checked a few out and read them. And in no time at all...

 

A whole new world of understanding about backgammon appeared for me!

It turns out that there is an "invisible" game of backgammon, with all sorts of rules and incredible strategies, that I knew nothing about.

Once I understood these rules, it didn't take long before I became a formidable competitor. In no time at all, I was able to hold my own against the tennis pros at my club. I even started to win back some of the money I had previously lost to them. And if I played against a less experienced player, I won just about every time...no matter what numbers showed up on the dice I was rolling.

The transformation was incredible! Even more importantly, it was REAL!
Just like Einstein, I had "discovered" a truth about life that was previously concealed to me and to most other people. And just like Einstein, once I discovered this new reality, I was able to do things and accomplish things with a greater degree of success and efficiency, not to mention much less STRESS!
Don't make the mistake of thinking this example doesn't relate to you! It does. There are countless other areas of life where your own views and understandings are similarly wrong or incomplete.

Take the area of marketing, for example. Some people have an understanding of the "invisible" game of marketing that allows them to sell millions of products, anytime they want. Others lack this understanding and quickly go out of business.

Look at human relationships. Most people fail to succeed in this important area of their lives. Why does this happen? Is it because they are defective? Is it because they lack the basic ability to succeed? Is it because they were physically or emotionally abused when they were children?

No. It's because they have faulty understandings of what it takes to succeed in this area of human endeavor, and because most other people around them have faulty understandings as well.

In order to succeed in the area of human relationships--and in many other areas of life as well--you need to be willing to question the wisdom of what everyone around you thinks and believes. In other words, you've got to be willing to reach down inside and pull out the Einstein within you.

You've got to be willing to find out what the real truth about human relationships is...and then you've got to have the courage and integrity to stay true to that truth...no matter what other people around you think, feel, or believe.

Might you antagonize certain people who feel threatened by your new or "unusual" perspective? Sure, you might lose a few friends. Einstein certainly did. But you'll soon gain a whole new group of friends and acquaintances who won't feel threatened and who will appreciate what you have to offer.

These are only two specific examples.

The same principle applies to an endless array of problems and issues. In order to produce a breakthrough in any of these areas, you've got to be willing to let go of your previous understandings. You've got to be willing, on your own or with the help of others, to see things quite differently than you currently see or understand them.

You've also got to expect this won't feel good or comfortable, at least not in the beginning. Feeling scared or upset is not necessarily a sign of trouble. It's often a positive sign that you truly are letting go and you are getting close to discovering some new truth. But there's also another part of you that will resist any new discoveries or insights every step of the way. After all, it means you probably won't ever be able to go back to your old way of thinking (and being).

That's pretty threatening to any of us.

And remember, like Einstein, you don't need to have proof or evidence, before you change your own personal thinking. Proof will often come later, once you've fully embraced and tested out your new ideas.
But also remember that, just like Einstein, you'd better be right about the ideas and principles you choose to guide you!

Going against the grain of public wisdom can be costly as well, especially if you choose a theory or viewpoint that's not solidly grounded in the way life actually works.

Well, there you have it--a not too technical account of how Einstein arrived at E=MC2. I hope you enjoyed this special report and that you take something useful away from it.

Wishing you good health, happiness, and much success,

-Yours
Vasishth Vyas.
(The PainKilleR.)

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