I so wish that time travel was possible. Not just because I wish I could go back in time and undo some of the mistakes I have made in my life, but because I would love to go back and undo some of the mistakes that others have made! For example, I would love to appear on the deck of the Titanic on April 15th 1912 and warn the Captain of impending doom. I would love to appear in the vicinity of Adolf Hitler just before his rise to power and put an end to his perverse ambition. I would love to appear in Dallas in 1963 to prevent the assassination of President Kennedy.
Alas, I am certain that time travel is not possible and the reason is as follows.
Like any of the physical things surrounding us, we are all made up of atoms. Protons, neutrons and electrons. The atoms that allow us to exist were not “born” at the same time we were born. They did not grow inside of us. They have existed, either as atoms or as other forms of energy, since the creation of the universe.
Whilst some atoms may undergo changes in arrangement from time to time, such as the chemical change from one compound to another, or undergo a sub-atomic change as occurs in the center of stars from one element to another, most atoms typically exist in one state for a very, very, very long time. An atom of hydrogen, for example, might bond with two atoms of oxygen to form a new atom of water, but the individual atoms of hydrogen and oxygen are still there. They have just changed their atomic arrangement to form a new substance with new properties.
As we grow and continue to live our lives, we accumulate atoms from the world around us, as well as lose atoms back to the environment. An atom of water, for example, was probably once part of an ocean, then evaporated into a could, falling as rain, possibly draining into a river, back into the ocean, another cloud etc until one day it was absorbed through the soil by a plant, then eaten by me or by an animal that I subsequently consumed. That very same atom is now (temporarily) part of me. There is an endless list of paths that the atoms that make up me may have taken before becoming me (or you).
Putting aside reality for a moment, imagine you could place a unique number on each atom in and around the earth, including the atmosphere, like the number on a pool ball. Suppose you could also then track specific atoms as they continuously move from one thing to another, observing the unique number on each atoms once it becomes something else in order to identify it. Of course this is a silly idea, but lets use it to illustrate a point.
Now, imagine you invented a time machine or found a stable worm hole that you could use to travel back in time and you attempt to do so. This is where the laws of physics will kick in, preventing success.
The reason is simple. It is impossible for you to exist at an earlier point in time, because the atoms that make up you (or anyone or anything else you wish to take back in time with you) already existed at the earlier point in history, as something or someone else. Using the imaginary illustration, if you were to make a list of all of the uniquely numbered atoms that constitute “you” and you were able to locate each numbered atom at the earlier point in time, you would discover those precise atoms were at various places across the planet existing as things other than you: perhaps part of certain bodies of water, various plants, rocks, minerals in the soil, animals, structures and even other people!
Unlike sub-atomic particles such as electrons, atomic particles can not exist in two different places at the same time. In other words, you can never exist at an earlier point in time when your atoms are already there, busy being something or someone else. Time travel is not possible due to a fundamental law of physics. Bummer.
NOTE FROM MODERATOR:
I think this is the LINK TO COLUMN: Is time travel possible? - The Straight Dope See my Post below (#21). – CKDH