Many worlds, many futures?

[Time_Traveller]

To return to the question that has puzzled thinkers since Newton's day, is the future preordained? Or are there an infinite number of futures? One way of looking at the quantum world suggests that not only are there an infinite number of futures, but they are realised in an infinite number of universes.

Photons and electrons sometimes behave as waves and sometimes as particles, but never both at the same time. So far, the argument for interference between one universe and another applies only to events occurring at the quantum level.

But the idea of parallel universes provides a possible resolution to the 'grandfather paradox' that might otherwise cause problems for time travellers. If we travel back in time and change history, we launch ourselves into a new future in a parallel universe - but we have no effect on the present one from which we started out.

Scientists of the future may well pursue a new form of futuristic technology based on quantum effects. Such applications could include quantum teleportation, by which a quantum particle can be teleported from one point in space to another; and quantum computation, where calculations can be carried out which would take many years on a conventional computer. Although we now know how to measure time very accurately, have we come any nearer to answering the basic question 'What is time?'.

What do you think?

[oldfruit]

Deep. Ask me again when i have had a few beers, lol:D

[FraserClarke]

. Such applications could include quantum teleportation, by which a quantum particle can be teleported from one point in space to another

That happened about 13 years ago...

[Tim]

I still think the answer is 42.

[daz]

Well, unless you are Neil Johnson from Oxford University, I think you should credit the original author......

BBC - Science & Nature - Space - Time Travel

[acey]

Neil Johnson didn't invent the grandfather paradox!

It's a great question and very old. Aristotle argued it like this: either it's going to rain tomorrow or it isn't. One or other must be true. So it's already decided which one it will be.

Not many people accept that idea now.

Classical physics (including relativity) is deterministic so implies that the future is pre-ordained, though in practice there is never enough information to make a perfect prediction: the only (classical) computer big enough to predict the future would be the universe itself.

There's an argument that even in the case of quantum computers this remains true: the universe can be considered a quantum computer which at every moment is calculating what happens in the next moment. See for example this book by Seth Lloyd:

Programming the Universe - Wikipedia, the free encyclopedia

David Deutsch, who also works on quantum computing, is an advocate of the Everett "many worlds" (i.e. parallel universe) scenario, and describes it in this book:

The Fabric of Reality - Wikipedia, the free encyclopedia

In a many-worlds scenario you would indeed have many futures and many pasts, thus resolving the grandfather paradox. That's pretty much how they did it in Back To The Future.

Most working physicists aren't much concerned about foundations of quantum mechanics, as long as they can make the sums work, hence remain agnostic about Everett's many-worlds. It's of more concern to quantum cosmologists, who take it very seriously. |See for example Max Tegmark's website:

The Universes of Max Tegmark

And when it comes to crediting original authors...

REVIEWS OF MODERN PHYSICS

[Ford Prefect]

I still think the answer is 42.

Im with TJ, now where did I leave my towel

[Jamie]

Neil Johnson didn't invent the grandfather paradox!

No one said he did!!!...

Daz was referring to the cut and paste job that makes up the whole of Time-Travelers post.

It was taken from the link provided in Daz's post..... Which Neil Johnson IS the author!!

Just thought i would point that out, Seeing as you seem to be hell bent on pointing things out to people i thought i ought to point this out to you.....

[daz]

Thanks acey

My point was that the OP simply copied the text from the linked site (or perhaps another) without credit or reference.

[acey]

Daz was referring to the cut and paste job that makes up the whole of Time-Travelers post.

I didn't read far enough into the linked article to see the piece at the end - thanks for putting me straight and well done Daz for being so keen-eyed!

[nebogipfel]

........ If we travel back in time and change history, we launch ourselves into a new future in a parallel universe - but we have no effect on the present one from which we started out.

Hello fellow Chronic Argonaut

Precisely, and that is why IMO Stephen Hawking is wrong when he states that time travel into the past is not possible ...... but what do I know?

PS

Perhaps Sabrina Lloyd is an alias ......

[ollypenrice]

It may be unfortunate that no credit was given for the original post but the question is still fundamental and worth sounding out. (BTW an academic friend tells the tale of a medical student who handed a shameless cut and paste piece of coursework to ... of all people ... its original author! Brilliant.)

Okay, there is a good but difficult book on time by Michael Lockwood, The Labyrinth of Time.

My own view is that we should very seriously doubt the validity, on a non-local scale, of the past-present-future flow which Lockwood calls the tensed theory of time. It is obviously very effective in our daily lives but I think it likely that this flow is somehow embedded in something larger, a multidimensional matrix of some kind. The observer inadvertently selects a set of local 'time circumstances' from within this larger matrix and in a sense creates the tensed flow of time then observed. A consequence of this selected/created flow is the notion of causality which may be as spurious as the flow itself.

(I'm reminded here of what is for me the spurious notion of 'purpose' in nature. I see no 'purposes' in nature, only consequences. Maybe cause and effect would go the same way if we could reach a broader understanding.)

I know this is arcane stuff but we are all astronomers and all fascinated by the remote, the mysteroius and the unknown and should never apologize for this...

Olly

[acey]

I've read the Lockwood book and agree it's very good (and not easy). The difficulty with embedding things in a "higher matrix" is that it doesn't really get round the basic problem of explaining "flow" (or transience). The simplest kind of "higher matrix" would be the block universe, where world-lines are fixed and effectively static. This doesn't explain why a point on a world line (e.g. my consciousness) experiences time as passing, with an asymmetry between past and future. Dunne's pseudo-scientific theory, "An Experiment In Time", supposes flow to be defined with respect to a higher dimensional time, itself flowing with respect to a higher one, ad infinitum.

Leibniz isolated the basic problem, which is to account for space and time in terms of things which are not themselves spatial or temporal. His monadology was an attempt at this, but needed recourse to a transcendental concept (God). Modern work on spin networks, loop quantum gravity etc (discussed in Smolin's book Three Roads To Quantum Gravity) has at least some superficial resemblance to Leibniz's network of monads.

Everett's many-worlds attaches crucial importance to consciousness, so this doesn't get round things either.

I think the idea goes back to Hoyle, of having data attached to local points such that they form a sequence: the analogy is numbered pages of a book, jumbled in any order, though our perception puts them in sequence. In that picture, sequence and causality are essentially a construct of our ordering. But it doesn't explain how the pages got numbered, why they make such a nice sequence in a particular order, and make little sense in any other.

[ollypenrice]

Thanks Acey for many interesting directions to follow up. Despite my lit background I had not come across Donne's contribution. However, his verse is packed with interesting astronomical allusion.

I must read the Smolin. I loved his Life of the Cosmos.

Olly

[Macavity]

Hang onto your hats folks, I'm just about to decide whether my lunch should be beans... or spaghetti on toast! Which of my many (gastronomic) universes would you prefer?

It is something that always puzzles me though. At what level do these (MY?) trivial decisions decide the fate of some... collective universe. I'm neither a fan of (Augustinian?) predestiny, nor of some infinite number of quantum futures?

[acey]

I had not come across Donne's contribution. However, his verse is packed with interesting astronomical allusion.

I was referring to J.W. Dunne, not John Donne - though the latter possibly met Galileo according to a new biography by David Wootton, so he's certainly not out of place in an astronomical discussion.

An Experiment with Time - Wikipedia, the free encyclopedia

[ollypenrice]

I was referring to J.W. Dunne, not John Donne - though the latter possibly met Galileo according to a new biography by David Wootton, so he's certainly not out of place in an astronomical discussion.

An Experiment with Time - Wikipedia, the free encyclopedia

Silly me! Too quick on the trigger. Thanks for the link.

JD may have met Gallileo? Amazing. I never knew that.

Olly

[acey]

The Donne meeting is speculative. On the other hand it has long been supposed that Milton met Galileo while in Italy.