Time travel is a tried and true
science fiction staple. It usually involves being able to fly in a spaceship
faster than the speed of light or diving through a wormhole. None of those technologies
currently exist in the real world of science.
Astrophysicists often discuss
wormholes: can one be created without a black hole as the door, would it be be
stable, would it be large enough to travel through without getting destroyed in
the process, and what kind of energy source might it take to create one? So far,
no one has any idea how to do any of that. NASA is currently testing an engine,
known as the EM Drive, which seems to have potential for faster than light
travel. But, as of now, no one even knows how it generates thrust.
Albert Einstein said that no
object with mass, like a spaceship, can go at the speed light as it would take
an infinite amount of energy to get there. He didn’t exactly say nothing could
travel faster than the speed of light. You might think that if it can’t travel
AT the speed of light, how can a spaceship go faster than the speed of light? Physics
allows for a phenomenon called “tunneling” where an object can be in condition
A and B but not in between. Physicists run rather simple experiments where
objects go from A to B even though they can’t be in between the two states. So
far, they’ve only done such experiments with objects like electrons, not
spaceships, but that may just be a matter of technology.
Scientists have also discussed
ways to create wormholes without a black hole doorway. It only takes a lot of
energy. Like a sun’s worth of energy, but still not impossible, in theory.
But here is the rub with time
travel. One of the most fundamental truths physicists know about the universe is
the conservation of energy. Since Einstein showed us that matter and energy are
intimately related via his famous equation E=MC2, the full conservation
rule is that the total amount of mass and energy must be conserved. It’s known
as the 1st Law of Thermodynamics.
Let’s say I want to travel back
in time to meet George Washington. Once I left this time, there is suddenly
less mass-energy in the universe now and there is suddenly more mass-energy in
the universe in 1776. It all averages out, but the 1st Law of
Thermodynamics is exact, not an average. This appears to make time travel
impossible.
Unless, somehow, the exact same
amount of mass-energy transfers from then to now at exactly the same instant I
go to then. But you might randomly take half a person from then and move him or
her to now.
I think I’d just leave it
alone.
On the first Tuesday of each month, I write an astronomy-related column piece for the Oklahoman newspaper. On the following day, I post that same column to my blog page.
This is reprinted by permission form the Oklahoman and newsok.com.
