Let's Get Rich!
It should be possible with Time Travel to become immensely rich.
All that the Time Traveller is required to do is to travel back in time and place a small amount of money in an interest earning account then return to the present and collect the money which will have increased in value due to the accumulation of the interest in the intervening years.
Although this type of trip is identical to that outlined in Holiday To The Past with the Time Traveller's World Line clock running at the same rate but at different positions on the Cosmic World Line in this case the Time Traveller's actions have an effect on events. Because the Time Traveller's action of opening an account effects the events that follow a paradox becomes apparent.
If the Time Traveller decides to open an account with a local bank 50 years earlier and place some money in the account then does he really need to travel back in time at all? Why does he not just go down to the bank and take the money out of the account? The first answer is that the Time Traveller has only thought about opening the account. The action of travelling to the past and opening the account although affecting the past occurs in the Time Traveller's future so naturally there will be no account if the Time Traveller goes straight to the bank. After the Time Traveller visits the past, opens the account and returns to the present a visit to the bank will find the account there.
The paradox this produces is a present where there is no account followed by a present where there is an account.
So the Time Traveller could visit the bank and meet the Manager on one day who would genuinely have no records of the account ever existing. However if the Time Traveller returned the next day after his trip to the past and met the Manager, who would remember him, to ask the same question the Manager would be surprised to find the account. How would the Manager explain this?
There appear to be at least two different views on how to resolve the paradox. The first involves Parallel Universes. With quantum physics there is inherent uncertainty. Many possible outcomes can occur but to us only one appears to occur. With Parallel Universe theory all the possible outcomes actually do occur each in their own universe. All these univereses then run parallel to each other. Our Universe is just one such Parallel Universe. There are as you can imagine many such universes. In fact, if you take all the possible outcomes of every possible action, and their outcomes, and their outcomes, etc for everything since the Big Bang it soon becomes apparent that there must be an infinite number of Parallel Universes.
Some of these universes will differ only slightly from our Universe (England win Euro 96) while others will be very different (The duck evolves to be the dominant species on Earth). When Time Travel occurs the Time Traveller returns to the past of our Universe but this action causes another universe to occur that runs parallel. Any actions that the Time Traveller makes will not effect the future of the Universe that the Time Traveller started from as this is now separate from the new universe that the Time Travaller is now in. All actions will effect only the new universe.
In our example the Time Traveller goes back 50 years and opens an account which starts a new parallel universe. If the Time Traveller is able to return to the Universe from which he started he will still find no account. The Time Traveller would have to return to the new universe where there is the account in order for there to be any financial benefit. However since this is a new universe created by the Time Travellers actions the events that followed in the 50 years are likely to be completely different from those in the Universe from which the Time Traveller started. The Bank may not even exist for example.
The second view on resolving this paradox is in two parts. Firstly there is the Chronology Protection Conjecture which suggests that it is impossible to make a Time Travel machine from something such as a wormhole. No one can then travel back in time so there can be no paradoxes. It has been said that the world is safe for historians!
The second part involves freewill and restraints of the Laws of Physics. In our example the Time Traveller has freewill and travels to the past to open an account. It may be however that should Time Travel be possible other currently unknown Laws of Physics would stop the Time Traveller from being able to open the account and thus change the past. Or perhaps the change may be allowed and the account is opened but events that subsequently occur in the following 50 years still result in there being no account when the Time Traveller returns to the present. Records are lost in a fire or the Bank merges with another for example. Again there are no paradoxes. This solution allows Time Travel to be possible but shows that the Universe is a pretty smart place and easily able to sort out any actions we Humans might cause!
The following takes this idea further with a full example which due to the above naturally has different endings.....-
Money, Money, Money -
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Anthony Edwards - December 1996