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.
Without going too deeply in the abstractness of this model, they re-envisioned space and
time as a pair of light cones.
One cone is the past, the other is the future connected by the present.
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.