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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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