|"Reverse the polarity of the neutron flow!"|
In Doctor Who it is often stated that you can't go back to a time earlier in your own lifetime because of the risk of meeting yourself. If you you break this rule you mustn't meet yourself or something nasty will happen.
It seems to me that in real life this is less of a problem than it appears. By the age of 25 there are very few (if any) of the atoms in your body that were there on the day you were born. In fact, at the time you were born most of your 25 year old atoms were in the bodies of other people or objects. Hmmm. This is often misunderstood because many body cells stay with you for your whole life, but those cells do regenerate and the atoms themselves will have swapped over many times.
If I, at the age of 44, go back and meet myself as a child the two people would be made up of completely different atoms. The only problem would be that my 44 year old atoms would exist in other people and objects. Rather than the two versions of me meeting and something nasty happening the likely outcome of travelling back in time would be that my atoms would take up their locations as they were at that point in time. As has often been said:
In every glass of drinking water there is at least one atom that passed through the bladder of Oliver Cromwell.
However, even given this problem the situation does raise an important existential question. If our bodies are not the same as 25 years ago then is our consciousness dependent on the physical hardware of the body? The only logical answer is - no. Our personality and memories are much less connected to the physical apparatus of our brains than we might like to think. This makes it entirely possible that human consciousness could exist in other atoms not directly linked to the body and therefore exist separately from the living body.