Theoretical physics is an unusual branch of science loaded
with interesting thought experiments, concepts and hypothetical devices. You
can find everything from cats being simultaneously alive and dead sealed in
cardboard boxes awaiting observation to Albert Einstein himself branding
quantum entanglement as "spooky" and hard to believe, which it sort
of is.
But one of the most odd concepts in theoretical physics stems
from Einstein's work. It's the concept of a type of particle called a tachyon,
and while still hotly debated, some argue that they could exist.
While science fiction authors have made much use of the word
tachyon, the hypothetical particles themselves are not currently part of the
standard model of particle physics. We've never seen one, nor any indication
that they might exist. It's merely that nature may allow for them to exist, and
if they did exist they would exhibit some very strange characteristics.
One would be that they always travel faster than light. But
it's worth noting that the speed of light really isn't quite the brick wall
that it's made out to be. Popular perception tends to be that the speed of
light is a sort of mythical universal speed limit that nothing can ever exceed.
But in reality, it only applies to normal matter, and the reason that it does
is pretty straightforward.
Whenever you push something that has mass, such as a rocket,
it requires that you expend energy to get it going. The faster you go, the more
energy you have to expend. This works on a sliding scale and as you approach
the speed of light, it requires more and more energy to accelerate further
until you reach a point, which is the speed of light, where you would need
infinite energy to go any faster. But, you can't ever have infinite energy.
Something that doesn't have mass in the same sense as a
rocket, such as a photon of light, propagates through the universe at the speed
of light. But relativity doesn't rule out an exact opposite state of affairs,
and that brings us back to the tachyons.
If they exist, they would not be able to slow down to the
speed of light because that also would require infinite energy. Opposite to
normal matter, the less energy a tachyon has, the faster it would travel. Add
energy, and it would slow down. But it gets even stranger.
Within relativity, there is an effect called time dilation.
This is one of the weirder properties of the universe, but it definitely
exists. Space and time are somehow linked, leading to the term space-time. As a
result of this, the faster you travel through space, the slower time ticks.
This is really a matter of acceleration. We tend to think of
gravity as a pulling force, it drags us down. And it does, but a better way to
state it is that gravity is an acceleration towards something. Big, massive
objects create acceleration towards them in nearby objects. As such, when you
accelerate your rocket in space, time slows down, but it also slows down the
closer you get to a gravity source.
So even sitting still here on earth's surface, you are still
feeling, as gravity, an acceleration
towards earth's center. This means that time is ticking slower for you than it
is for the astronauts on the ISS because they are a bit further away from earth
than you are.
While it may seem weird, we know that this is more than just
a prediction by Albert Einstein. Time dilation has very real world
implications. One of these is on the GPS system. For that system to work you
need some serious precision in timing, on the level of nanoseconds.
Trouble is, if clocks here on earth are ticking slower than
the clocks on the GPS satellites, then the timing errors would accumulate very
rapidly. So, we have to adjust and compensate for time dilation to make the
system work, and if we didn't it would take only about two minutes for the GPS system
to begin giving false results and it would grow to be increasingly off by about
10 kilometers per day. Any time you use the GPS system, it is actively being
adjusted for time dilation.
So, the faster you go the slower time ticks, but another
reason that you can't go faster than light is because the speed of light also
just happens to be the point at which time quote-unquote "stops".
It's a bit more complicated than that really, but we'll leave that for future
video. With the tachyons, given that they are traveling faster than light, they
would see the same effect in reverse. In short, they would always travel
backwards in time.
The existence of tachyons would have broad implications. If
they could be used to transmit information, then you could send messages to the
past. In 1907 Einstein advanced that faster-than-light communications would
create a causality paradox. This is a violation of intuitive cause and effect, where
cause does not lead to an effect, but the effect comes before the cause.
If you could communicate faster-than-light then you could
call yourself, or telegraph the past as Einstein termed it, and give your past
self stock market tips and get rich. This has been termed the tachyonic
antitelephone. But that we don't seem to be getting many calls from the future
could be telling as to whether all of this is possible, but the debate over it
continues.
Now, scientists have looked for tachyons. If they're streaming
at us from space, when you look for them they are predicted to look a lot like
a cosmic ray, but unlike cosmic rays they would be expected to reach a detector
on the ground before the particles produced by their entry in the atmosphere
because they would be moving faster. This has not been observed suggesting that
tachyons do not exist.
But there is a model that accounts for the absence of
tachyons and remains consistent with relativity itself. It comes from the work
of James Wheeler and Joseph Spencer, both of Utah
State University
The model is such that while relativity allows for tachyons
to exist, the model does not and the possibility for them unequivocally
disappears. Only years of debate within theoretical physics will a consensus on
this be formed.
But, as often happens in theoretical physics, you end up
with a whole other set of questions and oddness. This model also predicts
something rather disturbing. It would mean that the universe is deterministic. That
kind of a universe is uncertain because the universe appears really probabalistic
and even random on the quantum level.
But, some in quantum mechanics have dissented for years about
that. They have maintained that the randomness is only an illusion and have
kept the idea of determinism alive. Trouble is, a deterministic universe has
spooky implications of its own. It would mean that the future is already written
and set in stone. In such a case, we would merely be actors following a
pre-determined script.
Philosophers still debate what determinism means as far as
existence, but another aspect of time dilation and relativity is that not only
does time slow down for you as you go faster, relative to the world outside,
your space ship is, in fact, time traveling into the future.
That might imply that the future is set in stone and fully
deterministic. But in quantum mechanics, determinism continues to fall short.
How the two seemingly valid views reconcile is still an unknown, but as Shakespeare
once said "All the world's a stage", perhaps he was more right than
he thought.
Thanks for listening! I am futurist and science fiction
author John Michael Godier currently about to launch a second channel, more on
that in the next episode and be sure to check out my books at your favorite
online book retailer and subscribe to my channel for regular, in-depth
explorations into the interesting, weird and unknown aspects of this amazing
universe in which we live.
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