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Dark matter as matter in parallel universes...

by mrspeedybob
Tags: dark, explored, matter, parallel, universes
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Misericorde
#37
Jun3-11, 10:19 AM
P: 87
It doesn't exactly bowl me over than a name from Star Trek would be something you find cropping up in more than one forum related to science in general.

I keep hearing in this thread about dark matter as a product of universes other than our own, but even if possible (and twofish-quant has made that sensible), doesn't Occam's Razor cut far too close for that? I'd want to see native matter eliminated through process and trial before looking to other realities.
DavidMcC
#38
Jun4-11, 06:36 AM
P: 101
Quote Quote by Misericorde View Post
It doesn't exactly bowl me over than a name from Star Trek would be something you find cropping up in more than one forum related to science in general.

I keep hearing in this thread about dark matter as a product of universes other than our own, but even if possible (and twofish-quant has made that sensible), doesn't Occam's Razor cut far too close for that? I'd want to see native matter eliminated through process and trial before looking to other realities.
I don't see how "Occam's razor" can be defeat the right kind of multiverse - on the contrary. The problem of conventional, one big bang cosmology are very severe, in that nothing makes sense. Dark matter is but one little aspect of it. Slight parity violation in particle physics, the appearance of fine tuning of the universe for life (the values of the fine structure constant and strong interaction), the variability of the cosmological "constant", inflation, are all better explained by the right kind of multiverse (ie a "fecund universe" type once proposed by Smolin, but I don't want to go through that yet again, there are now so many threads on this , it gets tiresome). I suspect two things : (1) Smolin was too soon with this hypothesis, so that there wasn't enough evidence for it at the time, and (2) there were many rubbish versions of the multiverse, which do, indeed, just complicate things.
EDIT: Also, a single big bang is highly improbable if big bangs are a natural process. Therefore, we only DETECT one with light - the one we're in.
Chalnoth
#39
Jun4-11, 06:56 AM
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Quote Quote by DavidMcC View Post
I don't see how "Occam's razor" can be defeat the right kind of multiverse - on the contrary.
Yes, Occam's Razor actually prefers a multiverse, even if we don't look at any data. This simply comes down to the fact that within mathematics, it is much easier to get a class of objects than it is to get a single member of that class. So it is a unique universe, not a multiverse, that needs evidence to support it. And the fact is that all of the evidence that has any relevance to this question at all so far points more to a multiverse than it does to a unique universe.
Misericorde
#40
Jun4-11, 07:02 AM
P: 87
Let me rephrase: the notion of an infinite number of universes is not subject to Occam's Razor if you believe in eternal inflation, or a multiverse of many isolated pockets. It does cut finely (I think) in the case of QM interpretations such as MWI where it's just another variable to remove the "artifact" of collapse.
Chalnoth
#41
Jun4-11, 07:21 AM
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Quote Quote by Misericorde View Post
It does cut finely (I think) in the case of QM interpretations such as MWI where it's just another variable to remove the "artifact" of collapse.
In the MWI, there are actually fewer assumptions than in other interpretations. The MWI just assumes the wavefunction dynamics of quantum mechanics, full stop. Other interpretations assume some sort of collapse or other mechanism that looks like collapse. MWI just looks at the wavefunction dynamics and notes that the appearance of collapse is already there, no extra bells and whistles required.

This is just one example (among many) of why a multiverse is preferred over a unique universe.
twofish-quant
#42
Jun4-11, 07:43 AM
P: 6,863
In the interest of relating everything to observations, let me point out that a lot of the interest in parallel universes was inspired by recent observations of extra solar planets. It turns out that when we look at extra solar planets, that hot jupiters are very common, but we don't see them in our own solar system, which makes people wonder why our solar system seems to be specially tuned for life, and of course the answer is obvious. If our solar system had a hot jupiter, we wouldn't be here, and it turns out that the orbits of Jupiter and Saturn are specially tuned so that they are well-behaved.....

The other problem is that it turns out that in standard particle physics theories none of the fundamental constants are uniquely determined. The value of the fine structure constant at "zero energy" happens to be because the universe settled at this energy state after symmetry breaking happened.

So this got people thinking about how this applies to the whole universe. I know one scientist that wrote a critical paper on the possibility of multi-universes and he mentions this explicitly as one of the things that got him thinking about it.
DavidMcC
#43
Jun4-11, 07:58 AM
P: 101
Twofish-quant, I thought all the other observational reasons for suspecting a multiverse are actually rather more convincing than mere exoplanet tendencies, which have nothing much to do with the issue, as far as I'm concerned.
However, I agree about your second para.
Misericorde
#44
Jun4-11, 08:09 AM
P: 87
MWI has fewer than other interpretations except the only one that has any evidence to support it: shut up and calculate. I don't understand why people think they're going to form a valid ontology based on a theory which is not a "final" theory. Occam's Razor cuts closer to the bone than an attempt to rationalize why we don't recognize quantum behaviour in everyday life (dead/alive cats).

I'd add, if we're going to be willing to boil everything down to imponderables such as "before" the BB, or an infinite multiverse, eternal inflation, and so on... well... why not just say that this universe is all that there is, period. What's outside of the universe? Well, it's possibly as salient as asking for a before the BB; it's just not something human beings can contemplate; eternity, nothingness, a lack of time.

We wisely ignore those issues as being beyond the scope of physics, or at least not falsifiable or verifiable, right? Well, my view is that using the data we have now to even wonder about the 'why' of our existence and the ability of a universe or multiverse to support wondering organisms is predicated on failure. We have imperfect theories, but the benefit of them is the technology and progress they allow; I suppose if a final theory were developed then moving on to ontology would make sense, but right now it's hubris.
DavidMcC
#45
Jun4-11, 08:11 AM
P: 101
Quote Quote by Chalnoth View Post
Presumably you meant non-gravitational interaction. But then, if the dark matter wasn't that close to itself, it wouldn't be close to us either, and thus we wouldn't feel its effects very much.
It's a tricky point, Chalnoth. Maybe gravity simply has a short range in hyperspace, so we only feel the gravity from those bits that are very close in it, and by the same token, those bits are isolated from each other.
Chalnoth
#46
Jun4-11, 08:16 AM
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Quote Quote by twofish-quant View Post
It turns out that when we look at extra solar planets, that hot jupiters are very common, but we don't see them in our own solar system, which makes people wonder why our solar system seems to be specially tuned for life, and of course the answer is obvious.
Well, the difficulty here is that this is almost certainly a selection effect. Hot Jupiters have high masses and short orbital periods, and so are the easiest to observe. The fact that we see a lot of them seems to indicate more that planets in general are likely to be very common. In fact, given that within our own solar system, every one of the more massive planets has a plethora of moons argues rather strongly that nearly every star out there will similarly have a number of planets (though obviously the more violent star systems, such as, say, tight-orbiting binaries, may end up destroying any planets that form).

Quote Quote by twofish-quant View Post
If our solar system had a hot jupiter, we wouldn't be here, and it turns out that the orbits of Jupiter and Saturn are specially tuned so that they are well-behaved.....
Well, Jupiter and Saturn couldn't exist if their orbits weren't well-behaved, because our solar system is some 4.5 billion years old. Anything that wasn't well-behaved that was that massive would have collided with something over the billions of years our solar system has been around.
Chalnoth
#47
Jun4-11, 08:17 AM
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Quote Quote by DavidMcC View Post
It's a tricky point, Chalnoth. Maybe gravity simply has a short range in hyperspace, so we only feel the gravity from those bits that are very close in it, and by the same token, those bits are isolated from each other.
That doesn't help.

And by the way, in order to explain our own observations of gravity, gravity in a higher-dimensional space would have to be stronger than it is in our 3+1 dimensions, not weaker.
Chalnoth
#48
Jun4-11, 08:19 AM
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Quote Quote by Misericorde View Post
MWI has fewer than other interpretations except the only one that has any evidence to support it: shut up and calculate.
You mean the Copenhagen interpretation? Sorry, but that one has been falsified by observations of quantum decoherence.
Misericorde
#49
Jun4-11, 08:45 AM
P: 87
Quote Quote by Chalnoth View Post
You mean the Copenhagen interpretation? Sorry, but that one has been falsified by observations of quantum decoherence.
I mean exactly what I said: "shut up and calculate", not worry about collapse unless decoherence is the focus on your study. The solution to a falsified theory is not to invent countless interpretations of a theory, a majority of which are not falsifiable even if they are elegant. The solution is to calculate and work toward a greater understanding of what is right and wrong in the current formulation, observing and recording, and creating a NEW THEORY.

Clearly GR and QM have holes in them, but they also predict nature with astonishing fidelity. To assume that doesn't mean we have an infinite series of half-steps to a final theory however, again, seems like hubris. Shut up and calculate, and fine tune until we get so close it makes no difference, or we're all dust. It's good to identify the ontological problems uncovered, and some areas such as DCQE experiments demand explanation. I do not believe that interpretation of existing theories is of value in finding that however, but rather only new theories which are MORE predictive and explanatory. The rest is very admirable, but still very clearly intellectual masturbation.
Chalnoth
#50
Jun4-11, 10:07 AM
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Quote Quote by Misericorde View Post
I mean exactly what I said: "shut up and calculate", not worry about collapse unless decoherence is the focus on your study. The solution to a falsified theory is not to invent countless interpretations of a theory, a majority of which are not falsifiable even if they are elegant. The solution is to calculate and work toward a greater understanding of what is right and wrong in the current formulation, observing and recording, and creating a NEW THEORY.
Sounds like a hand-wavy excuse to stop thinking about it to me.

My entire point was that absent evidence to discern which way to go, we should always consider the explanation with the fewest assumptions to be the most likely. That's MWI. And it turns out that this has been confirmed by observations of quantum decoherence. To claim that there is still some "real" collapse besides simple decoherence is an unjustified and unjustifiable claim and should be considered nonsensical.
Misericorde
#51
Jun4-11, 10:33 AM
P: 87
Quote Quote by Chalnoth View Post
Sounds like a hand-wavy excuse to stop thinking about it to me.

My entire point was that absent evidence to discern which way to go, we should always consider the explanation with the fewest assumptions to be the most likely. That's MWI. And it turns out that this has been confirmed by observations of quantum decoherence. To claim that there is still some "real" collapse besides simple decoherence is an unjustified and unjustifiable claim and should be considered nonsensical.
There's nothing at all wrong with thinking about it, but there's thinking about it, and forming armed camps; I see far more of the latter.
twofish-quant
#52
Jun5-11, 08:04 AM
P: 6,863
Quote Quote by Misericorde View Post
There's nothing at all wrong with thinking about it, but there's thinking about it, and forming armed camps; I see far more of the latter.
The problem is that without any observational tests, then a lot depends on personal impressions which can be different from person to person. If person A thinks that MWI is simplier or more elegant than Cophenhagen and person B disagrees, there is really no way of resolving this argument. I think that Picasso is more elegant than Rembrandt, and you disagree. There is just no way of convincing each other.

The other problem is that Ockham's razor is a heuristic. Heuristics can be wrong. Also, you get into the issue of fewest assumptions. To argue that there is this other world in which I'm now shopping at a computer mall rather than typing in a computer, is just weird. Not to say that it's wrong, but it's weird.

Also, this is why some people (like myself) stay away from the whole argument is quantum interpretation. It's like listening to people debate religion. If you can figure out a way to come up with an experiment that shows that the Wisconsin Lutherans are right and the Missouri Luthereans are wrong or vice versa, then I'm interested, but otherwise I tend to tune out. If instead of talking about experimental data, we are using simplicity and elegance as determining factors for truth, then we are in the world of religion and fashion. Not that this is a bad thing, but it's something that I'm not personally interested in.

Having said that it turns out that people *have* suggested a very simple experiment that I can do that can confirm that MWI is correct. Google for quantum suicide. The cool thing about that experiment is that it will happen naturally anyway so if the quantum immortality people turn out to be right, I'll know about it in a few decades anyway. No need to rush things.

Finally, one other reason I personally don't think too much about this sort of thing is that I do sometimes worry about losing my grip on reality.

One really weird idea that I'd like to throw out as a question for someone else to work on the math. Suppose the MWI is correct and at every moment the universe is making multiple copies of itself. Also lets assume that that in all of those universes the laws of physics are not fixed. So that right now there are an infinite number of multiple universes forming with a different value of the fine structure constant. Now if the fine structure constant or the gravitational constant suddenly changed, I die. So at every moment, there is are infinite number of alternative universes forming and in all but a small fraction of them, I die. Now using some statistics, I ought to be able to come up with some statements about what I'm likely to observe. For example, there are going to be limits on how fast I observe Planck's constant or the fine structure constant changing, because if it changes too fast, I die. So at every moment, massive multiple copies of me are forming and dying, I ought to be able to figure this out by looking at some statistics.
Chalnoth
#53
Jun5-11, 09:15 AM
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Quote Quote by twofish-quant View Post
Having said that it turns out that people *have* suggested a very simple experiment that I can do that can confirm that MWI is correct. Google for quantum suicide. The cool thing about that experiment is that it will happen naturally anyway so if the quantum immortality people turn out to be right, I'll know about it in a few decades anyway. No need to rush things.
The main problem is that the whole thought experiment assumes that there is a stark dividing line between consciousness and death. In reality even the most violent of deaths turn out to be pretty gradual compared to the electromagnetic interactions that cause decoherence. Death is actually a gradual disintegration of consciousness compared to those interactions, and thus behaves quite classically.

This gradual disintegration of consciousness destroys the thought experiment because instead of a dead/alive situation, it's one of slightly less conscious vs. slightly more conscious with each step of decoherence, so that there isn't any selection effect keeping people conscious. And by the time the instant of death comes, your consciousness is already so fragmented that there still isn't any selection effect going on.

So there really isn't any reason to worry about quantum indeterminacy causing immortality.

Quote Quote by Mintmaster View Post
One really weird idea that I'd like to throw out as a question for someone else to work on the math. Suppose the MWI is correct and at every moment the universe is making multiple copies of itself. Also lets assume that that in all of those universes the laws of physics are not fixed. So that right now there are an infinite number of multiple universes forming with a different value of the fine structure constant. Now if the fine structure constant or the gravitational constant suddenly changed, I die. So at every moment, there is are infinite number of alternative universes forming and in all but a small fraction of them, I die. Now using some statistics, I ought to be able to come up with some statements about what I'm likely to observe. For example, there are going to be limits on how fast I observe Planck's constant or the fine structure constant changing, because if it changes too fast, I die. So at every moment, massive multiple copies of me are forming and dying, I ought to be able to figure this out by looking at some statistics.
Well, this doesn't apply to reality, however, because such changes in the laws of physics couldn't be global changes, so that if they happened with any frequency, we'd see them happening elsewhere in the universe. We don't, so it's wrong. Whatever determines the low-energy laws of physics must make them stable enough that we wouldn't have observed any change in them for the history of the observable universe.
Lost in Space
#54
Jun5-11, 09:27 AM
P: 125
Regarding the quantum immortality thing, doesn't it all really boil down into whether things are infinitely probabilistic (speculatively speaking of course)? How many chances in infinity would it necessitate to be immortal in one or more universes? Isn't the chance one in infinity? If one was immortal in more than one universe, would one still be one? Shouldn't decoherence ultimately resolve the paradox down to a single factor where, if at all possible, one could only be immortal in one universe?


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