As far as we know, it's not possible for a person to move at
twice the speed of light. In fact, it's not possible for any object with the
kind of mass you or I have to move faster than the speed of light.
However, for certain strange particles, traveling at twice
the speed of light might be possible – and it might send those particles back
in time.
A universal speed limit
One of our best physical theories at the moment is the
theory of relativity, developed by Albert Einstein. According to this theory,
the speed of light operates as a universal speed limit on anything with mass.
Specifically, relativity tells us that nothing with mass can
accelerate past the speed of light.
To accelerate an object with mass, we have to add energy.
The faster we want the object to go, the more energy we'll need.
The equations of relativity tell us that anything with mass
– regardless of how much mass it has – would require an infinite amount of
energy to be accelerated to the speed of light.
But all of the sources of energy we know of are finite: they
are limited in some respect.
Indeed, it's plausible the Universe only contains a finite
amount of energy. That would mean there isn't enough energy in the Universe to
accelerate something with mass up to the speed of light.
Since you and I have mass, don't expect to be traveling at
twice the speed of light anytime soon.
Tachyons
This universal speed limit applies to anything with what we
might call "ordinary mass".
There are, however, hypothetical particles called tachyons
with a special kind of mass called "imaginary mass".
There is no evidence tachyons exist. But according to
relativity, their possible existence can't be ruled out.
If they do exist, tachyons must always be traveling faster
than the speed of light. Just as something with ordinary mass can't be
accelerated past the speed of light, tachyons can't be slowed down to below the
speed of light.
Some physicists believe that if tachyons exist, they would
constantly be traveling backwards in time. This is why tachyons are associated
with time travel in many science fiction books and movies.
There are ideas that we might someday harness tachyons to
build a time machine. But for now this remains a distant dream, as we don't
have the ability to detect potential tachyons.
Shortcuts?
It's disappointing we can't travel faster than the speed of
light. The nearest star to us, other than the Sun, is 4.35 light-years away.
So, traveling at the speed of light, it would take more than four years to get
there.
The farthest star we've ever detected is 28 billion
light-years away. So you can pretty much give up on charting the entire
Universe.
That said, relativity does allow for the existence of
"wormholes".
A wormhole is a shortcut between any two points in space.
While a star might be 4.5 light-years away in normal terms, it might only be a
few hours away via a wormhole.
If there are any actual wormholes, they would let us travel
great distances in a very short period of time – allowing us to get to the
farthest reaches of the Universe within a single lifetime.
Unfortunately, like tachyons, wormholes remain entirely
hypothetical.
Strange possibilities
Despite the fact we can't genuinely travel faster than
light, we can still try to imagine what it would be like to do so.
By thinking in this way, we are engaging in
"counterfactual thinking". We are considering what things would, or
might, be like if reality was different in some way.
There are many different possibilities we could consider,
each with a different set of physical principles.
So we can't say with any certainty what would happen if we
were able to travel faster than light. At best, we can guess what might happen.
Would we start to travel back in time, as some scientists think tachyons might
do?
I'll leave it to you and your imagination to come up with
some ideas!
Reference:
Sam Baron, Associate professor, Australian Catholic University.
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