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Uncommon Descent Contest Question 14: Is backwards or forwards time travel really possible? Winner announced


This was another one for physics buffs. Contest 13, here, asked: “The Large Hadron Collider is back up and running, but why?” The question there was whether what we would learn is worth nine billion dollars. Two physicists have suggested that Hadron’s woes are due to particles travelling back in time. Their theory has been received with the amusement one might expect, but it raises an interesting question, one that is a staple of sci-fi literature – is forward or backward time travel possible, even for particles?

This time the question was:

For a free copy of the Privileged Planet DVD, about the unique position of Earth, provide the clearest answer to this second question: Is backwards or forwards time travel really possible, even for particles? Why or why not? What are the consequences if it is true?

Before I announce the winner, I would like to thank Access Research Network for kindly offering a shelf of books by mathematician David Berlinski – a self-confessed Darwin skeptic and widely enjoyed wit – as prizes for future contests. You can view their catalogue here.

The winner is:

IryniaB for this very short post at 1:

“Is backwards or forwards time travel really possible, even for particles? Why or why not? What are the consequences if it is true?”

No, it’s impossible. First, because it violates conservation of energy; second, because we would have noticed time travelers by now – and we haven’t. If it is true, I will invest all my money in a time traveling company. But since I don’t, that proves it’s impossible.

I am not sure that IrynaB’s argument proves that time travel is impossible, but it identifies a significant barrier to acceptance.

It’s hard to imagine that people in the future would not wish to go back to the past to find out what happened. Many problems could be sorted out by seeing exactly what happened in disputed events, or reading exactly what was written in later-lost books. Yet we have never seen anything of the kind or had any reason to suspect it.

Similarly, while we are all travelling together into the future at an even rate, surely many people would urgently want to jump ahead, in order to know to know – if they could- what is scheduled to happen, and see if they could change it. Of course, we can’t do that yet; thus, we cannot know if it will ever be possible. But we should certainly have seen some time travellers from the future coming back here in the past.

I call this the unicorn problem. Strictly speaking, a horse-like creature with a horn could possibly have existed, but apparently it never did, apart from imaginative artwork. The reason I don’t believe in unicorns is that none have turned up.

I wouldn’t have believed in the duck-billed platypus either, except that it exists. (Classified as a mammal, it lays eggs and the males apparently have a poison gland in the hind foot, a practice unknown to other mammals, but common in reptiles.)

In some of these matters, we may need to assess the state of the evidence as much as the state of the theory.

IryniaB needs to provide me with a valid postal address at oleary@sympatico.ca, in order to receive the prize.

A couple of other comments (I am sorry I cannot give proper attention to all comments – lack of time, not lack of interest):

Gods iPod, at 2 and 5, be sure to advise us of your book when it is available.

Mapou at 8, I was much interested in your comment, but unclear what the equations mean. I sense, as you do, that there is something squishy in the state of much current cosmology. Inspired by your comment, I will try to sponsor more contests on this, but must acquire additional relevant prizes.

Heinrich at 9 and 10 , some kinds of backward time travel are really possible, as long as we do not take it literally. For example, a common practice in my country, when laws change, is that existing situations are “grandfathered.” Even though a given arrangement is technically illegal as of July 1, 2xxx, all pre-existing arrangements, some stretching far back into the past, are exempted from prosecution. This can be seen as a form of time travel, to protect the people involved from too great a dislocation. But no person is going back. Only certain interpretations of information are going back. The granfathered scheme is ruled legal even though if fronted at a later time, it would not be.

Magnan at 14, re the time traveller who is away one year and finds himself back 100 years later and his spouse dead (we will pass over in silence his honest reaction to that news): I wonder whether there is a limit to how much one can fiddle with time. After all, that happens with space, matter, and energy too. In theory, an animal could be a half kilometre high, but in practice, it could not happen for reasons of physics. Have we any reason to believe that similar constraints might not affect time travel, assuming it is possible?

GFrancis at 17, I agree with you that bizarre cosmological theories – a Missed Universe pageant, if ever there was one – often prop up atheism. Indeed, were it not for the presumption of atheism, I doubt that many of them would receive much attention. And I don’t think they help us understand our universe better.

Thanks to all for a great discussion! Now some fun: Brigadoon, a musical comedy about a Scottish village that moves into the future:

If you would like to enter future contests, periodically announced, here are the contest rules, not many. Winners receive a certificate verifying their win as well as the prize. Winners must provide me with a valid postal address, though it need not be theirs. Names are never added to a mailing list. Have fun!


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