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

[RJM Corbet]

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.

So what could Hawking really have meant by saying there can only be universes with the same laws of physics as our own? How would you interpret it? (For the layman, lol?)

 

[Venusian Broon]

So what could Hawking really have meant by saying there can only be universes with the same laws of physics as our own? How would you interpret it? (For the layman, lol?)

Let's go down the rabbit hole...

Okay, first I should state, I'm not and was never a cosmologist - did a lot of 'bog standard' Quantum mechanics instead - so I'm sure I'm missing loads of details

However, after getting slightly baffled at the BBC article (sometimes things can be oversimplified too much!) I pulled up the paper to take a look.

Hawkings-Hertog are looking at a form of the Eternal Inflation multiverse (here is an article I thought was quite nice in explaining this idea: Eternal Inflation and Colliding Universes)

So basically it is a 'multiverse' that is constantly inflating, peppered throughout with bubble universes - small patches of energy and matter. These smaller universes will continue to expand, but because they have formed can no longer keep up with the inflationary 'speed' of the mother multiverse. (It gives me the image of currants in a bun, if the bun was infinite and forever expanding ) We are, of course, one of these bubble universes in this model, and if the multiverse is eternally inflating, then there will be an infinite number of universes produced.

Originally when they had first proposed this theory in the 1980s, there was no way of telling if all these bubble universes were similar and in fact it was proposed that you would get a random set of conditions in each. This leads to the problem of that it is all just random chance that we find ourselves in a universe well suited to us. Which might be possible, but is a rather unsatisfactory explanation of where we came from!

So in this paper they have modelled a series of 'toy' universes (using gauge-gravity duality to model its Quantum wave function - this is where the connection with String Theory comes in) at the brink of exiting inflation and have calculated that it appears that there is a high probability that only a small range of bubble universes, measured via their boundaries, can come into existence at this point. Other weirder or radically different ones are essentially just not very likely at all.

They then state: "we conjecture that eternal inflation produces universes that are relatively regular on the largest scales."

So I suppose they are not saying that all the universe do have the same laws as ours, but instead conjecture that they should all, because of their formation, be reasonably similar. And I suppose therefore, by corollary, the laws should be similar.


However,

Note that:

- The Eternal Inflation model has it's own problems, it is not necessarily how our universe was formed*.
- They used simplified models of universes and more realistic model may not give the same results.
- And given what I said about QM interpretations above, the Eternal Inflation multiverse is not the same thing as the Many-body multiverse - that is a different beast! Also I believe the multiverse that might be built using M-theory (string theory) using 10-11 spatial dimensions is totally different again.


---------------------------------------------------
* In fact until we can experimentally find another universe how can we actually be sure that any multiverse actually exists?. To be fair, there are tentative suggestions that there might be imprints of another universe in the microwave background radiation, but really, it's not obvious that's the case.

 

[RJM Corbet]

Let's go down the rabbit hole...

Okay, first I should state, I'm not and was never a cosmologist - did a lot of 'bog standard' Quantum mechanics instead - so I'm sure I'm missing loads of details

However, after getting slightly baffled at the BBC article (sometimes things can be oversimplified too much!) I pulled up the paper to take a look.

Hawkings-Hertog are looking at a form of the Eternal Inflation multiverse (here is an article I thought was quite nice in explaining this idea: Eternal Inflation and Colliding Universes)

So basically it is a 'multiverse' that is constantly inflating, peppered throughout with bubble universes - small patches of energy and matter. These smaller universes will continue to expand, but because they have formed can no longer keep up with the inflationary 'speed' of the mother multiverse. (It gives me the image of currants in a bun, if the bun was infinite and forever expanding ) We are, of course, one of these bubble universes in this model, and if the multiverse is eternally inflating, then there will be an infinite number of universes produced.

Originally when they had first proposed this theory in the 1980s, there was no way of telling if all these bubble universes were similar and in fact it was proposed that you would get a random set of conditions in each. This leads to the problem of that it is all just random chance that we find ourselves in a universe well suited to us. Which might be possible, but is a rather unsatisfactory explanation of where we came from!

So in this paper they have modelled a series of 'toy' universes (using gauge-gravity duality to model its Quantum wave function - this is where the connection with String Theory comes in) at the brink of exiting inflation and have calculated that it appears that there is a high probability that only a small range of bubble universes, measured via their boundaries, can come into existence at this point. Other weirder or radically different ones are essentially just not very likely at all.

They then state: "we conjecture that eternal inflation produces universes that are relatively regular on the largest scales."

So I suppose they are not saying that all the universe do have the same laws as ours, but instead conjecture that they should all, because of their formation, be reasonably similar. And I suppose therefore, by corollary, the laws should be similar.


However,

Note that:

- The Eternal Inflation model has it's own problems, it is not necessarily how our universe was formed*.
- They used simplified models of universes and more realistic model may not give the same results.
- And given what I said about QM interpretations above, the Eternal Inflation multiverse is not the same thing as the Many-body multiverse - that is a different beast! Also I believe the multiverse that might be built using M-theory (string theory) using 10-11 spatial dimensions is totally different again.


---------------------------------------------------
* In fact until we can experimentally find another universe how can we actually be sure that any multiverse actually exists?. To be fair, there are tentative suggestions that there might be imprints of another universe in the microwave background radiation, but really, it's not obvious that's the case.

Thank you! That's a very understandable account, VB. Lots to think about.

So here's the question: If the multiverse theory is really there not simply as an extension of the super-tiny extra dimensions of M Theory, but really to provide a possible explanation for the 'fine tuning' coincidences of physics that make our macro universe possible -- such as the cosmological constant, etc -- then how is all this going to impact on the anthropic concept of infinite universes of every possible sort -- where we inhabit this particular universe, with these particular laws, because it's the (only) one that allows our existence?

Whew! That's a long sentence! But is it a reasonable question? Am I getting the proper gist?

Thanks again.

EDIT: Sorry I have edited that question several times to get it into shape.

 

[Onyx]

I don't think that there is an big coincidence going on. The anthropic principle pretty much means that the kind of life that pops up in a universe is going to be a product of that universe's physics, rather than just a happy coincidence. If physics didn't allow for life, than we wouldn't be here to remark on that. There could be universes outside the multiverse that are either much worse or much better for the creation of life, but that doesn't have anything to do with our multiverse.

Imagine buying 4 beans and planting them in concrete, iron filings, snow and damp soil. When the bean planted in soil grows, is that a coincidence? If you gave away the other three beans right after you planted them, what would your assumptions about planting beans be? 100% of the beans you observed grew, but only 25% of the beans you planted did.

 

[RJM Corbet]

I don't think that there is an big coincidence going on. The anthropic principle pretty much means that the kind of life that pops up in a universe is going to be a product of that universe's physics, rather than just a happy coincidence. If physics didn't allow for life, than we wouldn't be here to remark on that. There could be universes outside the multiverse that are either much worse or much better for the creation of life, but that doesn't have anything to do with our multiverse.

Imagine buying 4 beans and planting them in concrete, iron filings, snow and damp soil. When the bean planted in soil grows, is that a coincidence? If you gave away the other three beans right after you planted them, what would your assumptions about planting beans be? 100% of the beans you observed grew, but only 25% of the beans you planted did.

Yes, but the multiverse theories are there purely to prop-up the anthropic principle? It is very much conjecture with nothing approaching a shred of experimental evidence? Of course you will see where I'm going with this, which is not permitted in these particular forums ...

 

[logan_run]

We cant say a multiverse exist because we never been to one.

 

[RJM Corbet]

Of course. Taken to the extreme we end up not only with another universe where a monkey with a pencil writes Hamlet purely by chance, but with infinite such universes? Was Hawking unhappy with this logical progression of infinite other universes, and trying to limit them?

But limiting their nature makes coincidences like the cosmological constant (fine tuned to 1 x 10 to the power 120) ridiculously unlikely as result of pure chance (monkey with pencil) and even more difficult to understand, especially when added to all the other fine-tunings, the electron/proton balance, etc?

 

[Onyx]

Yes, but the multiverse theories are there simply in order to validate the anthropic principle? It is very much conjecture with nothing approaching a shred of experimental evidence? Of course you will see where I'm going with this, which is not permitted in these particular forums ...

I don't think so. There's the quantum "multiverse", which is a product of how our universe/multiverse deals with uncertainty.


And then there's the completely separate idea of any other universe that might exist outside of those rules. It might not have physics that would cause an internal "multiverse" due to uncertainty. It may have rules that cause life, or not. And there is nothing about the physics of our universe that would predict that such a place or places exist - they don't need to. It is simply an idea that, like there is more than one star and galaxy, maybe there are more than one universes. But if there are they don't have to operate anything like what we are able to even conceive of.

The "multiverse" could just be called the "universe" with the understanding that it includes all the timelines that we can't perceive, but are otherwise all descended from the same starting point as ours. That's something discreetly different than the very speculative suggestion that there could be completely separate "universes" that have zero connection to ours in origin, physics or time.

 

[RJM Corbet]

But what I'm saying is that multiverse theories are so conjectural that the alternative is at least equally likely: that we inhabit the only universe we can or will ever be able to prove or perceive?

 

[Onyx]

But what I'm saying is that multiverse theories are so conjectural that the alternative is at least equally likely: that we inhabit the only universe we can or will ever be able to prove or perceive?

I'm not able to follow the math sufficiently well to determine just how conjectural it is. No one has seen dark matter, so it could be said to be conjecture as well. But if the math that describes the physics of our universe doesn't leave any room for anything but the multiverse, then it isn't just a daydream.

Mind you, I don't think it is likely to ever be important. There's nothing in these theories that makes it likely that the branches of the multiverse can interact and change what's in your lunch pail to what Universe 617 Corbet packed. But it may explain why certain types of calculations work.

 

[RJM Corbet]

Ha! Yes, but dark matter (or something) really does exist. There's too much gravity without it. Dark energy is the only explanation of the expanding universe. String theory is properly trying to chase down quantum gravity? These are all objective science. But multiverse theories are actually ideological, if you get my drift?

 

[Onyx]

Ha! Yes, but dark matter really does exist. There's too much gravity without it. Dark energy is the only explanation of the expanding universe. String theory is properly trying to chase down quantum gravity? These are all objective science. But multiverse theories are actually ideological, if you get my drift?

Not really. Dark matter is a way of explaining a gravity problem without actually having a substance to point at. It could be that we simply don't understand gravity, and there are alternative theories that are based on the idea that we are doing the math wrong. Hawking wasn't just doing goof-off physics while the dark matter guys were doing the real work.

Maybe it would be more useful to say "The math of the universe may require that everything operate as if there is a functioning multiverse." Not that anyone has proved anything, but there is little functional difference between "as" and "as if" when you can't actually pull back the veil to check.

 

[RJM Corbet]

Or maybe you could say that the math of the existing universe would operate perfectly well without any conjectured multiverse? But the anthropic principle would not, lol?

 

[Onyx]

Or maybe you could say that the math of the existing universe would operate perfectly well without any conjectured multiverse? But the anthropic principle would not, lol?

I realize you're joking, but I don't see any connection between the multiverse and the anthropic principle.

 

[RJM Corbet]

If you spin a combination lock back and forward enough times you will eventually hit the right combination purely by chance. Or if you keep typing in random letters and numbers you will eventually hit the password? If there are enough other universes around, eventually ours will pop out purely by chance. It's the monkey with a pencil.

The anthropic princople has to assume multiple other universes as the only way to explain the fine tunings that make the existence of life possible.

So, what if there aren't any other universes?

 

[Onyx]

If you spin a combination lock back and forward enough times you will eventually hit the right combination purely by chance. Or if you keep typing in random letters and numbers you will eventually hit the password? If there are enough other universes around, eventually ours will pop out purely by chance. It's the monkey with a pencil.

The anthropic princople has to assume multiple other universes as the only way to explain the fine tunings that make the existence of life possible.

So, what if there aren't any other universes?

That may be, but those aren't necessarily the "other universes" implied by the quantum multiverse.

But the main point of the anthropic principle is that universe must automatically be compatible with the life that exists and observes it. Not that it had to come to be via a certain process.

 

[RJM Corbet]

Or put it another way: it doesnt matter how greatly the conditions suitable for life existing in 'our' universe -- and especially of life spontaneously arising from them -- (as a once-off string of coincidences) ignore all possible reasonable laws of chance by factors way beyond the sum of all the atoms in the universe, because the fact we're here proves it did happen?

 

[Venusian Broon]

So here's the question: If the multiverse theory is really there not simply as an extension of the super-tiny extra dimensions of M Theory, but really to provide a possible explanation for the 'fine tuning' coincidences of physics that make our macro universe possible -- such as the cosmological constant, etc -- then how is all this going to impact on the anthropic concept of infinite universes of every possible sort -- where we inhabit this particular universe, with these particular laws, because it's the (only) one that allows our existence?

Whew! That's a long sentence! But is it a reasonable question? Am I getting the proper gist?

Thanks again.

EDIT: Sorry I have edited that question several times to get it into shape.

Don't apologise! These are tough issues, I think, to really grasp. I struggle constantly with them when I am called to think about them! But it's fun

I have been busy for a day, so I couldn't get back to you - however it meant that I was thinking about your questions and the whole issue of the anthropic principle. (Although not when I'm doing 16kg kettle bell snatch intervals, they be b*tches for holding any coherent thought other than 'I must...get...through...this')

Firstly I have to say before I get into details, the anthropic principle, of whatever flavour, could indeed be the truth. It really just comes down to belief at this point. A lot of the concepts we talk about with regards to multiverses/string theory/anthropic principle etc. are so far from being experimentally verified that they are barely science.

So why am I (and others) 'lukewarm' on the anthropic principle?

The weak anthropic principle - that the reason we, intelligent beings, exist is that the conditions are right. This essentially, in my mind, becomes a tautology. Why do we exist? Because the conditions are correct for our existence. Why are the conditions correct for our existence? Because if they weren't we wouldn't exist.

It's a scientific cul-de-sac. I believe we don't advance our scientific knowledge of our cosmic origins if you believe this.

The strong anthropic principle - that the universe must have properties that allow intelligent life to develop lead to the following suggestions:
- The universe was designed to produce intelligent life. This is the sort of universe that religious people ascribe to, of course. But it also describes Simulation universes. Both I have yet to see any evidence for so I am dismissive of this idea, although as a Fortean I am open to all ideas. (Just give me the evidence. I'm not Woo-Woo, but a hard-nosed scientist!)
- The universe needs an intelligent observer to come into being. This is a 'cosmic Copenhagen interpretation' universe. The first observer caused the universe to 'Quantum mechanically collapse' from its imaginary status to a real state. I mentioned it in my post above about QM interpretations that there is still a lot of discussion about what an 'observer' and 'measurement' really mean so I think this suggestion is really just an artefact of a (likely) misunderstanding of QM.
- An ensemble of universe are required for the existence of our universe. This is the position Eternal Inflation model was in, in the paper we've been discussing in this thread. If the original proposition was true then there are infinite universes and it is just random chance that we are in the 'right one'. Again this is, I feel, an unsatisfactory answer. It doesn't let us delve deeper.

So what does the Hawkings paper do that gets us away from the final ensemble argument of the strong anthropic principle?

-Firstly they conjecture that purely from automatic consideration of how small elements of space-time interacts with the multiverse, they naturally give rise to universes that are like ours. We do not need to invoke design, the arrival of intelligent beings or postulate that every single variation must be generated.
-It is an extension of the Copernican principle. To summarise: Copernicus shifted the Earth from the centre of the universe to being one of a number of planets that orbited the sun. We have since extended this. Our sun is just an average star, we are in a unremarkable galaxy, and in a galaxy cluster that looks like many other galaxy clusters. Now our entire universe is just an average universe in some random place in a vast multiverse. I think hubris is damaging so feeling cosmically average is a good thing .


Honestly, it's almost pure belief. I can't substantiate this with proper evidence. But I wish to always go to the path of allowing continuing scientific progress.

 

[dask]

If you build it they will come?

 

[RJM Corbet]

Fortean:

Fortean Phenomena

Charles Fort - Wikipedia

I had to Google it, lol ...
(Just don't tell Brian Cox, ok?)
Thanks VB