Stephen Hawking's last paper: multiverses follow the laws of physics

Brian G Turner

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#1
The BBC reports that Stephen Hawking's last paper has been published, in which he tackled the idea of multiverses and asserted that they must follow the same laws of physics as in this universe:
Prof Hawking's multiverse finale

On the surface, it sounds simple enough, though I doubt most people would understand the maths involved. :)

However... we've seen it suggested before that at least some mathematical constants may actually change over time.
 

RJM Corbet

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#2
The BBC reports that Stephen Hawking's last paper has been published, in which he tackled the idea of multiverses and asserted that they must follow the same laws of physics as in this universe:
Prof Hawking's multiverse finale

On the surface, it sounds simple enough, though I doubt most people would understand the maths involved. :)

However... we've seen it suggested before that at least some mathematical constants may actually change over time.
"The ... assessment indicates that there can only be universes that have the same laws of physics as our own."

Meaning that all our constants (although they might change miniscually over billions of years) are true and fixed. So it still leaves such problems as why do the charge of election and proton of hydrogen balance each other so exactly? That and many other unlikely coincidences that make physical existence possible at all?l
 
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Onyx

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#3
"The ... assessment indicates that there can only be universes that have the same laws of physics as our own."

Meaning that all our constants (although they might change miniscually over billions of years) are true and fixed. So it still leaves such problems as why do the charge of election and proton of hydrogen balance each other so exactly? That and many other unlikely coincidences that make physical existence possible at all?l
Everything seems unlikely when you only have one example to work from. There might be plenty of universes unrelated to ours that are soupy messes with no phyical matter possible.
 

RJM Corbet

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#4
Everything seems unlikely when you only have one example to work from. There might be plenty of universes unrelated to ours that are soupy messes with no phyical matter possible.
But Hawking is limiting them to universes that obey the laws we know? That's a big step back from infinite multiverse? I don't know ...
 
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Onyx

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#5
But Hawkins is limiting them to universes that obey the laws we know? That's a big step back from infinite multiverse? I don't know ...
The multiverse that Hawking is talking about is essentially all of the branchings of our original universe that are necessitated by quantum theory. It is like saying that all life on earth uses DNA because the first life used DNA.

I'm pointing out that you could step outside of that starting point and say - what if there were other universes with completely independent starting points; would they be like ours? The answer should be no, because those places aren't descendants of our quantum universe. Just as alien life might be organized around something besides DNA, and not obey chemical laws dictated by DNA based life. Hawking is talking about a specific kind of "multiverse", not all possibilities.
 

RJM Corbet

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#6
The multiverse that Hawking is talking about is essentially all of the branchings of our original universe that are necessitated by quantum theory. It is like saying that all life on earth uses DNA because the first life used DNA.

I'm pointing out that you could step outside of that starting point and say - what if there were other universes with completely independent starting points; would they be like ours? The answer should be no, because those places aren't descendants of our quantum universe. Just as alien life might be organized around something besides DNA, and not obey chemical laws dictated by DNA based life. Hawking is talking about a specific kind of "multiverse", not all possibilities.
Well I don't know exactly what he's saying because I can't do quantum maths. The quantum 'sum of all possible paths' (possibilities) I believe actually results in the vast number of such infinite possibilities cancelling each other out. So in reality it's a mathematical probability device that in reality leaves, for instance, the electron close within its most probable atomic radius.

Although semantically it could be anywhere in the universe, mathematically it's hugely vanishingly unlikely to be anywhere else but close within the atomic radius? Or ionised, but close by? Well, I don't really know.

So the 'infinite multiverse' sounds philosophically nice, but perhaps in his old age Hawking was really concluding that although infinitely many possibilities theoretically do exist, in reality they will largely cancel each other out and leave a reality close to that created by our own 'laws of nature'?
 
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Onyx

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#7
Well I don't know exactly what he's saying because I can't do quantum maths. The quantum 'sum of all possible paths' (possibilities) I believe actually results in the vast number of such infinite possibilities cancelling each other out. So in reality it's a mathematical probability device that in reality leaves, for instance, the electron close within its most probable atomic radius.

Although semantically it could be anywhere in the universe, mathematically it's hugely vanishingly unlikely to be anywhere else but close within the atomic radius? Or ionised, but close by? Well, I don't really know.

So the 'infinite multiverse' sounds philosophically nice, but perhaps in his old age Hawking was really concluding that although infinitely many possibilities theoretically do exist, in reality they will largely cancel each other out and leave a reality close to that created by our own 'laws of nature'?
Given the most simple view, that the multiverse is the documentation of all possible atomic paths, what would be the mechanism for cancellation? On a macro scale, you could go home or to the store: What about your decision to go home makes the version of you that decided on the store stop existing?
 

RJM Corbet

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#8
Given the most simple view, that the multiverse is the documentation of all possible atomic paths, what would be the mechanism for cancellation? On a macro scale, you could go home or to the store: What about your decision to go home makes the version of you that decided on the store stop existing?
Well, mostly because the random quantum possibilities can't ever be translated up to the movements of the macro physical experience, although they underpin it?
 

RJM Corbet

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#9
It's something like: if you thtow a ball,
you place a clock at every point in infinity, the clocks reading 12 o clock cancel those reading 6 of clock, those reading 3 cancel those reading 9 etc.

The further away you go, the more there are revolutions of the clocks until it's only some clocks that dont make a full revolution that don't cancel each other? So the ball could land on Mars, but the overwhelming possibility is that it'll land closer? I think? Lol ...

EDIT: But of course they're not clocks measuring time, more like points on a wave.
 
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Onyx

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#10
Well, mostly because the random quantum possibilities can't ever be translated up to the movements of the macro physical experience, although they underpin it?
Schrodinger's Cat suggests that they can produce at least two paths. Even a multiverse with a few branches is a multiverse.
 

RJM Corbet

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#11
Schrodinger's Cat suggests that they can produce at least two paths. Even a multiverse with a few branches is a multiverse.
Ha! But everybody knows a real cat can't be both dead and alive at the same time? Lol. He was trying to illustrate quantum paradox?

EDIT: I don't think Hawking is rejecting multiverse, but infinite multiverse?
 

Onyx

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#12
Ha! But everybody knows a real cat can't be both dead and alive at the same time? Lol. He was trying to illustrate quantum paradox?

EDIT: I don't think Hawking is rejecting multiverse, but infinite multiverse?
I don't think anyone suggested anything was infinite. The number of branches comes from the finite number of particles and the finite life of the universe.

And the Cat isn't a paradox. It is an example of how quantum events can have simple macro sized effects.
 

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#13
Schrodinger's Cat is a thought experiment.
The unseen cat inside the box might be either dead or alive.
It can't be both. However we can't say which it is until we look in which case we either go on into the live cat universe or the dead cat universe.

You might say that the live cat universe is the optimist universe whereas the dead can universe is the pessimist universe. Unless you don't like cats then its the other way around.

Which leads to that inverse thought experiment where the cat is wondering whether the scientist outside the box is an cat lover or not.

It may be too soon to say that there are only universes that have our laws of physics. It could be that in some dimensional plane our physic like universes look like the bubbles on bubble-wrap that is all twisted together to almost coexist 'near' each other and that the flat areas around the bubbles are other universes that are too strange and that if we could travel to the other universes somehow; they would be the ones that are like ours and not the flat areas.

Anyway it would probably be easier to visit other Earths in other universes than to travel all the way to another habitable planet out there somewhere. Or maybe just as hard.
 
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Onyx

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#14
Schrodinger's Cat is a thought experiment.
The unseen cat inside the box might be either dead or alive.
It can't be both. However we can't say which it is until we look in which case we either go on into the live cat universe or the dead cat universe.

You might say that the live cat universe is the optimist universe whereas the dead can universe is the pessimist universe. Unless you don't like cats then its the other way around.

Which leads to that inverse thought experiment where the cat is wondering whether the scientist outside the box is an cat lover or not.
I understood the experiment to show how observation collapses the wave function and determines whether the cat had lived or did die due to the as yet undetermined atomic decay. So it might be proper to say that it is "both", unless you truly don't believe that the act of observation is what completes the process.

But regardless of what happens, we only have access to one or the other version of events, so it is essentially the same thing. But if you care about parallel universes running on the software, then it might be beneficial to look at the cat in a less deterministic way.
 

RJM Corbet

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#16
But in a universe where for example the proton and electron had slightly different charges, atoms couldn't form and matter couldn't exist. If the cosmological constant was slightly different the universe would either have collapsed or flown apart immediately before it could form, etc. The electron exclusion principle, the speed of light, the Planck constant, the gravity constant. Laws of physics?
 
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Onyx

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#17
But in a universe where for example the proton and electron had slightly different charges, atoms couldn't form and matter couldn't exist. If the cosmological constant was slightly different the universe would either have collapsed or flown apart immediately before it could form, etc. The electron exclusion principle, the speed of light, the Planck constant, the gravity constant. Laws of physics?
I agree. You might have some universes that are soup, and others that have physics that cause the level of organization ours have, but with entirely different principles.
 

RJM Corbet

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#18
I agree. You might have some universes that are soup, and others that have physics that cause the level of organization ours have, but with entirely different principles.
I'm sure some future generations will look back on our standard model physics as we do at Newton's: inspired and functional for purpose, but the tip of the iceberg?
 

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#19
Time needs also to be considered... if a universe is close to being in balance it can last a long time before it decays into whatever mush is out there. The consequence for a multiverse is that there will be universes formed at the same time as ours, but are mushifying now as I type this. Only the more stable physics-wise will continue beyond the now. A lot of those will mushify in the future. What will happen is that fewer and fewer 'stable' universes that started at the same time as ours will stay in existence.

Of course we might have (and I think this is highly likely) universes starting their existence after ours and the same paradigm will exist for those universes.

Now here's an idea for Dr Who - he time travels to another universe where he has to slightly alter one of the laws of physics of physics constants!
 

Venusian Broon

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#20
I suggest that what it might prove is that the observer becomes a part of the experiment; which is something that needs to be taken into account with most if not all experiments.
There are many different interpretations of QM, all giving the same results but radically different universes/multiverses.

There are many-world interpretations (heavily favoured by cosmologists), local hidden variable interpretations (favoured by those who thought Einstein was on the right track) and Copenhagen interpretations (heavily favoured by experimental physicists and probably still the bulk of the physicist community), but there are a great many more.

Point is most of these don't have problems with the 'observer' and the Copenhagen interpretation has been criticised for a very vague definition of what constitutes a measurement. I shan't go further here but there does seem to be a philosophical problem with having subjective observers essentially destroying the deterministic nature of the wave equation. So I think at first you have to clear up what you mean by Observer. And I don't think we are near there at all!

Of course, generally speaking, as all interpretations give the same equations, we physicists tend to mostly fall into the 'shut up and just calculate it' school of thought. ;):D
 

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