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Einstein Education
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Question:
Is it possible to travel back in time? I have seen theories that say
its not possible to go back in time, but it might be possible to somehow travel
in space whereas the traveler does not age.
Replies:
It is indeed possible to cause the time frame for one traveler to be
strikingly different from another by simply changing their relative
speeds. It has been done! But, hold on. It is not practical for
people yet. In particle accelerators like the one at Fermi Lab, protons
and anti-protons are accelerated to near (key word here - near - only near)
the speed of light. Their masses increase and their "lifetimes" increase.
This was discovered in cosmic rays years ago. Scientist discovered certain
mesons (if memory serves correctly on the type of particle) in cosmic rays.
They were surprised to find them in the rays on the surface of the earth.
You see, these particles had to travel through the earth's atmosphere to
get to the ground level. It takes a certain amount of time to travel clear
through the earth's atmosphere. These particles are moving at very near
the speed of light. At their speed it took them a certain amount of time
to get through the atmosphere. However, practical knowledge of these
particles dictated that they should disintegrate almost instantly
upon hitting the atmosphere. Nevertheless, they get here in spite
of their extremely short half-lives. Why? At near light speed, their
half-lives to us seem much longer. To the particles themselves they did
disintegrate as fast as ever. Why the difference? Time dilation. Can we
actually go back in time? I do not think so. See the response to the other
query on time travel in this section.
It is indeed possible to cause the time frame for one traveler to be
strikingly different from another by simply changing their relative
speeds. It has been done! But, hold on. It is not practical for
people yet. In particle accelerators like the one at Fermi Lab, protons
and anti-protons are accelerated to near (key word here - near - only near)
the speed of light. Their masses increase and their "lifetimes" increase.
This was discovered in cosmic rays years ago. Scientist discovered certain
mesons (if memory serves correctly on the type of particle) in cosmic rays.
They were surprised to find them in the rays on the surface of the earth.
You see, these particles had to travel through the earth's atmosphere to
get to the ground level. It takes a certain amount of time to travel clear
through the earth's atmosphere. These particles are moving at very near
the speed of light. At their speed it took them a certain amount of time
to get through the atmosphere. However, practical knowledge of these
particles dictated that they should disintegrate almost instantly
upon hitting the atmosphere. Nevertheless, they get here in spite
of their extremely short half-lives. Why? At near light speed, their
half-lives to us seem much longer. To the particles themselves they did
disintegrate as fast as ever. Why the difference? Time dilation. Can we
actually go back in time? I do not think so. See the response to the other
query on time travel in this section.
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Update: June 2012
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