Fine tuning and the multiverse

[John Oats]

Hi
New to this forum. I am not a physics student but someone with an interest in aspects of physics, particularly cosmology. This is a question regarding fine tuning and the multiverse as a possible answer. The following is a link to a Youtube video in the Closer to Truth series, and the interviewee is David Deutsch.

One of the questions asked is about the perceived fine tuning problem. The question is asked first in the video at 3.20 and the mulitiverse idea at 4.55. In Deutsch's answer to the multiverse explanation being unsatisfactory is that the overwhelming number of universes that contain life that is asking the question (why us?), is only just about doing so, in other words has only just reached the point where it can ask the question of itself. He also mentions Feynman having the same conclusion.
I am not clear about exactly what he means by the overwhelming number of universes being only just capable of answering the question. I have emailed Deutsch but he answered with, Buy my book, its explained in Chapter XYZ. So, I bought the book and the explanation in the book is written in such a way that I am still not clear. Can anyone please explain what is meant by this? My guess is that my not understanding is due to the answer being clear in Deutsch's head but not having been well communicated. I also, can't find any references to Feynman stating the same or similar. I have searched but can find nothing.
Hope someone can help here.
Thanks
John

 

[PeroK]

Hi
New to this forum. I am not a physics student but someone with an interest in aspects of physics, particularly cosmology. This is a question regarding fine tuning and the multiverse as a possible answer. The following is a link to a Youtube video in the Closer to Truth series, and the interviewee is David Deutsch.

One of the questions asked is about the perceived fine tuning problem. The question is asked first in the video at 3.20 and the mulitiverse idea at 4.55. In Deutsch's answer to the multiverse explanation being unsatisfactory is that the overwhelming number of universes that contain life that is asking the question (why us?), is only just about doing so, in other words has only just reached the point where it can ask the question of itself. He also mentions Feynman having the same conclusion.
I am not clear about exactly what he means by the overwhelming number of universes being only just capable of answering the question. I have emailed Deutsch but he answered with, Buy my book, its explained in Chapter XYZ. So, I bought the book and the explanation in the book is written in such a way that I am still not clear. Can anyone please explain what is meant by this? My guess is that my not understanding is due to the answer being clear in Deutsch's head but not having been well communicated. I also, can't find any references to Feynman stating the same or similar. I have searched but can find nothing.
Hope someone can help here.
Thanks
John

For what it's worth, I'd didn't understand or agree with his reasons for either hypothesis being rejected:

1) For the "creation" hypothesis, we know nothing about the universe in which our universe has been created. We cannot conclude anything about the laws of physics in that universe.

2) For the multiverse hypothesis, if we were one of the universes where the structure was a fluctuation, then we'd have come and gone. As long as it's possible for the laws of physics to be "created" in such a way that a stable universe is possible, then those stable universes may exist and we are in one of them.

In general, all of these lines of argument suffer from the problem that if there is something outside our universe, then we know nothing about it. So, no argument about what is and isn't possible can be watertight. Arguing on the basis of what we see in our universe and extrapolating that to say what a multiverse can and cannot do seems fundamentally flawed.

PS It's interesting that you could find no reference to Feynman having initiated this anti-multiverse argument.

 

[kimbyd]

Hi
New to this forum. I am not a physics student but someone with an interest in aspects of physics, particularly cosmology. This is a question regarding fine tuning and the multiverse as a possible answer. The following is a link to a Youtube video in the Closer to Truth series, and the interviewee is David Deutsch.

One of the questions asked is about the perceived fine tuning problem. The question is asked first in the video at 3.20 and the mulitiverse idea at 4.55. In Deutsch's answer to the multiverse explanation being unsatisfactory is that the overwhelming number of universes that contain life that is asking the question (why us?), is only just about doing so, in other words has only just reached the point where it can ask the question of itself. He also mentions Feynman having the same conclusion.
I am not clear about exactly what he means by the overwhelming number of universes being only just capable of answering the question. I have emailed Deutsch but he answered with, Buy my book, its explained in Chapter XYZ. So, I bought the book and the explanation in the book is written in such a way that I am still not clear. Can anyone please explain what is meant by this? My guess is that my not understanding is due to the answer being clear in Deutsch's head but not having been well communicated. I also, can't find any references to Feynman stating the same or similar. I have searched but can find nothing.
Hope someone can help here.
Thanks
John

I think what he's trying to say is that if we have a large multiverse where we have different observable universes which vary in their ability to support life, the general expectation from what we know of physics is that nearly all such universes won't be able to support life at all. And most of those that are able to support life will only barely be capable of it.

These kinds of arguments rest upon some assumptions about the precise ways in which the low-energy physics can vary from place to place. The main support they have is the fact that every proposed fundamental law that we've ever come up with that is remotely plausible has the property that most resulting observable universes won't support life at all.

So, then, the argument is that if we have this diverse kind of universe, then there should be a lot of features of fundamental physical laws (that is, physical constants) would result in a universe that is incompatible with life if they were tweaked just a little bit in the wrong direction. A multiverse where most of the multiverse is dead predicts the appearance of fine-tuned physical constants.

 

[John Oats]

Hi
Thanks for the answers. I guess the problem non-physicists face is definition of terms, or meaning of terms. From videos I have seen, it depends on who is giving their opinion as to what is meant by multiverse. Some suggest that multiverse means many millions or billions of discreet universes, all of which are incapable of communicating with or observing any other universe. Others seem to suggest that a multiverse is a universe that contains areas that may have different physical laws that are more sympathetic or unsympathetic to life arising. I am not clear which version Deutsch means. Either way he appears to be saying that he doesn't like the multiverse idea to explain fine tuning. To those of us that have had no background in physics, a huge number of universes, (either discreet universes or a universe with varying areas of physics), where one of the universes (or an area of a single universe) happens to have constants that permit life, seems to be a reasonable offering for why we experience fine tuning. Its simply a question of numbers. We won the lottery because the winning ticket just happens to be ours. Deutsch suggests that there must be a law of physics that explains it, rather than a lottery result. I guess then we are into the murky area of why life can only arise with the constants we see, or at least within a slim window either side. I guess it may come out that life as an emergence is simply a feature of the constants we see, and that universes with other constants may have other emergent features that we don't see and can't imagine. Is that perhaps what Deutsch means by his preferred option?

John

 

[Grinkle]

Some suggest that multiverse means many millions or billions of discreet universes, all of which are incapable of communicating with or observing any other universe. Others seem to suggest that a multiverse is a universe that contains areas that may have different physical laws that are more sympathetic or unsympathetic to life arising.

John -

As far as I know there is no model for a stable boundary between different laws of physics, so I think any region with a distinct set of laws of physics is going to be incapable of communication with or observing any region with a different set of laws. Whether these regions are described as isolated regions within a single universe or as discrete universes I think is as much a matter of poetry as it is of physics, but I may be ignorant of a meaningful distinction in those descriptions.

Listening to the interview, at first I thought Mr Deutsch meant that our universe is too hospitable for the anthropic principle to explain our existence. In other words, this universe is perfect for us and statistically it should be just barely survivable. Then I after listening more I landed on @PeroK 's interpretation that he meant we (or any feature of our universe) should not last very long and our universe is too stable and regular in its evolution for the anthropic principle to explain our existence.

A couple analogies -

There are many ponds on Earth where fish might just barely live. So a fish in a perfect pond might not be justified in saying the reason it is so fortunate to be in that pond is that it can't be found in any other environment - the only potentially existing environments where it even might be able to live is the perfect pond it finds itself in. Such a fish would not be making a valid anthropic argument - there are lots and lots of barely survivable brackish nasty ponds the fish would be more likely to find itself in. Unless it can find a reason it ended up in a perfect pond, it must conclude it is a lucky fish after all.

There are many ponds on Earth that dry up. A fish in a long lasting pond would (imo) be correct in saying the long lasting pond is the only type of pond it can exist in long enough to ponder the question of its own existence. IMO this fish is making a valid anthropic argument - so if I did understand Mr Deutsch correctly, then I am missing something about his reasoning.

 

[PeroK]

There are many ponds on Earth where fish might just barely live. So a fish in a perfect pond might not be justified in saying the reason it is so fortunate to be in that pond is that it can't be found in any other environment - the only potentially existing environments where it even might be able to live is the perfect pond it finds itself in. Such a fish would not be making a valid anthropic argument - there are lots and lots of barely survivable brackish nasty ponds the fish would be more likely to find itself in. Unless it can find a reason it ended up in a perfect pond, it must conclude it is a lucky fish after all.

There are many ponds on Earth that dry up. A fish in a long lasting pond would (imo) be correct in saying the long lasting pond is the only type of pond it can exist in long enough to ponder the question of its own existence. IMO this fish is making a valid anthropic argument - so if I did understand Mr Deutsch correctly, then I am missing something about his reasoning.

I think that is his argument. My point is that unless you can know and understand the variety of ponds, then you cannot infer anything. In fact, unless you understand your sample space, I would say you cannot appeal to probability theory at all!

Suppose you make a study and find 1 million ponds on Earth and only one perfect pond with some happy fish in it. The argument is that the happy fish cannot believe how lucky they are and conclude that the other 1 million poorer ponds can't exist. But, yet, they do!

So, I'm agreeing with you.

 

[John Oats]

Hi. Thanks for the responses. Yes I agree with the fishpond idea. There are gradations of habitable environments either side of "perfect", and those gradations make up the vast majority of environments capable of supporting life, but maybe not to the stage of evolution where life asks the question. There maybe only one environment (structured by constants) or a tiny number greater than one, where life survives to ask the question. That, as far as I can tell, is the popular view amongst cosmologists. Deutsch is saying he doesn't like that view, and that although he doesn't know what the answer is, he suggests it must be due to a particular law of physics, and not a lottery where if you guess all the right numbers you win the big prize, but if you guess some of the right numbers you win a lesser prize. This particular law of physics Deutsch thinks may be the cause of the apparent fine tuning, or rather explaining the fune tuning, is likely to be an emergent property of the initial conditions of the universe, leading to an energy soup, then atoms (and the stuff atoms go on to build - stars and matter), (possibly other) emergent properties from the initial formation of matter/energy such as mass, scale, time, then atoms forming molecules, molecules to complex chemistry, then organic chemistry, then basic life and so on. So maybe he means that we are emergent from the constants of nature because we are the only things that can be emergent from this set of constants, and that any future emergence will come through us, or other lifeforms in the universe, rather like a fern unfurling. We shouldn't therefore be surprised at our existence because our names are on the rota from the beginning, its just that now we have seen it pinned to the noticeboard.

John