While time travel may seem like a phenomenon found only in movies
like Back to the Future and The Terminator, science reveals this
may not be the case.
According to physicists, real-life time travel can occur within
a kind of feedback loop where backward movement is possible, but
only in a way that is "complementary" to the present.
In other words, people can only go back in time and look around
but cannot do anything that would alter the present they left behind.
Debunking the Time Travel Paradox
One of the biggest myths surrounding time travel is the idea that
if one goes back in time they could, theoretically, do something
to change the present. The new model, which uses the laws of quantum
mechanics, tosses that famous paradox out the window.
Clearly the present has never been changed by roguish time-travelers,
simply due to the fact that people don't suddenly fade out of existence
because a rerun of events has prevented their births. Therefore,
time travel is either:
- Simply not possible.
- Or, something is acting to prevent any backward movement from
changing the present.
While the former option may seem the most logical, Einstein's general
theory of relativity has led physicists to suspect the latter.
Using Einstein's Theory of Relativity
According to Einstein, space-time can curve back on itself, allowing
time-travelers to double back and meet the younger versions of themselves.
A team of physicists from the United States and Australia claim
this situation can only be the case if there are physical restrictions
protecting the present from changes in the past.
These restrictions exist because of the weird laws of quantum mechanics,
though (traditionally) they don't account for a backward movement
in time. Quantum behavior is ruled by probabilities:
Before something has actually been observed, there are many other
possibilities regarding its state; however, once its state has been
measured, those possibilities are cut down to only one, eliminating
all uncertainty.
To put it plainly, quantum mechanics discerns between something
that might happen and something that did happen. For example, if
someone doesn't know if their father is alive--if there is only
a 90 percent chance he is alive--then there is a possibility one
can go back in time and kill him. But, if one's father is alive
in present time, then there is no chance he can be killed in the
past.
Ahh, the mysteries of quantum mechanics ...
BBC
News June 17, 2005
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