Gravity and the Multi-verse?

[Wolfman]

Now here's a really interesting article from the Globe and Mail newspaper in Canada; it has a lot of different information, but at the end it says that some physicists now theorize that the reason why gravity is such a weak force compared to the other three forces in nature (electromagnetism, weak atomic force, and strong atomic force) is that our universe is just one of billions...and that while the other three forces are constrained only to our own universe, gravity acts throughout multiple universes, thereby diluting its effect within our own universe.

I noted upon reading this article a second time that while Professor Nima Arkani-Hamed supports the idea of multiple universes, he does not himself mention this idea of gravity being 'diluted'; this idea comes from an entirely unrelated website, hiddendimensions.org. When I went to check out this website, I have to admit that its design looks decidedly woo-ish. So would appreciate comment from others who may be more knowledgeable in this area. The idea of multiple universes is certainly one that is well-established within certain portions of the physics community, including many top physicists. But this is the first time I've heard this explanation of gravity -- is it also an idea supported by reputable physicists, or is it something that's been added to this article just to make it 'juicier', without any real scientific support?

As a side note -- is anyone here familiar with the "Spirit of Math" teaching program described in this article? It sounds like it would be a really great thing...too bad it is seen as being too much trouble to actually implement.

Physicist's guiding star put universe at his feet
ANTHONY REINHART
From Monday's Globe and Mail



WATERLOO, ONT. — Young as he still is at 34, Professor Nima Arkani-Hamed was far younger when he walked into a high-school classroom and found proof that the universe was, indeed, expanding.

...snip...

 

[TobiasTheViking]

This is also part of M-Theory, and there is another hypothesis like this as well.

I haven't read your quote yet but i assume it is woo, the two i mention, though, are not.

 

[Stimpson J. Cat]

The idea I had heard concerning the multiple-universe/gravity connection was that gravity may not be an actual independent force at all, but instead just a perturbation of the other forces due to nonlinearity in Schroedinger's equation.

It goes as follows. Schroedinger's equation, which describes the evolution of the quantum wave-function over time, is linear. It is this fact which results the wave-function being a linear superposition of all possible outcomes. The big question is then, what causes the wave-function to collapse into a specific outcome?

The answer provided by the many-worlds interpretation is that it doesn't. Basically the idea is that before we ask what causes the wave-function collapse, we should be sure that there is one. If we ask the question "what would the universe look like if there was no collapse, and the wave-function just went on as a linear superposition of all possibilities?", we find that the answer is "Exactly the way this universe looks".

The reason for this rather counter-intuitive result is that linear superpositions don't interact with each other. For example, if I shine two flashlight beams through each other, they go right through each other with no change. The electromagnetic field is (at normal energy densities), linear.

That's where gravity comes in. We can ask the question "What if Schroedinger's equation is only approximately linear?". This is a natural question to ask, because every other example of something being mathematically linear in nature, has turned out to only be an approximation. In particular, we can ask what we would expect if Schroedinger's equation were only approximately linear for low energy densities, with additional non-linearity appearing as energy densities increase.

What we would expect to see in such a case would be what appears to be an additional force. One whose strength increases with increasing energy density. It is conceivable that gravity is such a phenomenon. In effect, this would make gravity an interaction between these different (no quite linearly superposed) branches of the wave-function. In other words, interactions between universes.

I am not an expert on QM, General Relativity, or on the various attempts to unify them, so I can't really comment on how feasible this possibility is in light of current evidence, but it seems plausible to me.


Dr. Stupid

 

[AmateurScientist]

M-theory may be sexy and tantalyzing, but it really is little different from science fiction. It postulates grand fantasy worlds existing parallel with our own, but which remain completely unaccessible and unobservable to us. As such, their existence is no more important or useful to us, even if it were true, than the existence of Omicron Persius 9.

AS

 

[andyandy]

there's a great article in this weeks's NS about gravity...

According to legend, it was Galileo Galilei who first performed one of science's most famous experiments. After dropping a pair of cannonballs of different weights off the top of the Leaning Tower of Pisa, he heard the two balls hit the ground at the same instant. In this way he proved what physicists would later call the principle of equivalence: all objects fall at the same rate, regardless of their mass or composition, provided there are no forces acting on them other than gravity.

Whether or not Galileo really performed this experiment, it is the prototype of an iconic demonstration in physics, requiring only a pair of weights and a vacuum chamber to eliminate air resistance. The equivalence principle that it demonstrates has meanwhile become a cornerstone of Einstein's general theory of relativity, the model of gravity that has reigned for nearly a century.

Now two physicists at Stanford University in California, Mark Kasevich and Savas Dimopoulos, are preparing to challenge this whole premise, with a modern Tower of Pisa. Rather less picturesque than the Tuscan original, theirs is a shaft dug 10 metres down from a basement laboratory. Instead of dropping cannonballs, they will launch rubidium atoms upward and watch them fall down again. To measure the rate of descent, they will use an exquisitely sensitive timing method. The result: a test of the equivalence principle and general relativity far more stringent than any that has gone before.

Why would they want to do that? Because, says Dimopoulos, "there is something big that we don't understand about gravity". Researchers believe we may find a breach in the principle of equivalence or general relativity if we look hard enough, and that this would give us a major clue to what is missing. A breach could, for instance, reveal the first evidence for exotic new particles or extra dimensions of space that have long been postulated by theorists, including Dimopoulos. It could help physicists arbitrate between several proposed theories of quantum gravity that strive to unify gravitation with the other forces of nature.

http://www.newscientist.com/channel/fundamentals/mg19325901.600;jsessionid=JDPDLNCNAMDG

I'd love to post the whole article - but it's about 3000 words long....so this is just a tantalising introduction

Gravity dilution seems to be an accepted theory at least....indeed it's referenced in the article...

Dimopoulos and others proposed in 1998 that gravity operates in extra dimensions of space beyond the three we can see, and that this dilutes its apparent strength in the everyday world. The idea came from string theory, the leading approach to quantum gravity, in which extra dimensions of space contain vibrating loops of "string" that give rise to all the familiar forces and particles. Trouble is, this idea can only be tested if we probe at suitably small scales - something that is technically difficult, to say the least.

it's just the testability of the theory that's been (and will likely continue to be) problematic

 

[Wolfman]

Thank you very much for your responses, guys! However, I'd like to clarify my question.

I'm quite familiar with the idea of a multiverse, and personally have no problem with it. And I'm familiar with the idea that gravity is diluted through different dimensions.

But this article I quoted doesn't talk about gravity being diluted through different dimensions; it talks about gravity being diluted through different universes. Which are two entirely different things. When we talk about gravity being diluted through different dimensions, those dimensions are still located within the framework of our own universe (although many of those dimensions may act/interact on a level that is beyond our ability to observe directly).

It postulates grand fantasy worlds existing parallel with our own, but which remain completely unaccessible and unobservable to us. As such, their existence is no more important or useful to us, even if it were true, than the existence of Omicron Persius 9.

Well, if it turned out that gravity was actually affected by interaction with other universes, that would certainly have implications for us here in our own universe.

 

[INRM]

Now for the silly question...

Will this new larger super-sized particle accelerator create a black-hole?

Hey someone had to ask it!

 

[Ziggurat]

We can ask the question "What if Schroedinger's equation is only approximately linear?".

[nitpick]What you mean is, "What if Schroedinger's equation is only a linear approximation?"[/nitpick]

The equation itself is undoubtedly linear. Reality might not be.

 

[Fnord]

"... some physicists now theorize that the reason why gravity is such a weak force compared to the other three forces in nature (electromagnetism, weak atomic force, and strong atomic force) is that our universe is just one of billions...and that while the other three forces are constrained only to our own universe, gravity acts throughout multiple universes, thereby diluting its effect within our own universe."

Woo.

More specifically, this is an implication of "String Theory," which is woo, in that it has only been hypothesized, and not proven with any real, physical experiment.

There is no physical proof of the existance of any universe other than our own. It's all woo ... multiverse ... wooniverse ... it's all the same.

 

[andyandy]

More specifically, this is an implication of "String Theory," which is woo, in that it has only been hypothesized, and not proven with any real, physical experiment.

There is no physical proof of the existance of any universe other than our own. It's all woo ... multiverse ... wooniverse ... it's all the same.

Because something hasn't been proved true does not make it false. if something can not be proved true does it make it false? No - it's merely unknowable. I think the best physical proof we have of other universes is some form of multiverse anthropic reasoning - based on the unlikeliness of boundary conditions.


The standard model of elementary particle physics has more than 20 adjustable paramters - including the mass of all the basic, stable elementary particles, the basic coupling constants, and various angles of interaction. The standard model of cosmology has about another 15 parameters...

Now how these 35 or so parameters are determined ranks as one of current science's greatest mysteries - this can be broken down into two specific problems, the first of which is the naturality problem - these parameters are extremely small, or extremely large numbers. In planck units the cosmological constant is 10^-120, proton and neutron masses around 10^-19....
the second is the complexity problem - the remarkable circumstances for universal complexity require the fine tuning of these parameters into tiny windows - as an example, were the neutron heavier by 1%, a proton lighter by 1%, an electon's charge 20% stronger etc. there would be no stable nucleui - no stars. The universe would just be hydrogen gas.

But even worse, any attempts to unify these parameters through string theory, to explain that actually they are interdependent, has actually increased the parameters - so that even the simplest supersymetric expansion of the standard model now contains over 100 parameters.....

take away any multiverse reasoning, and by our current understanding, the universal big bang boundary conditions sufficient for our universe are ridiculously, astromically and stupendously unlikely.....

 

[Fnord]

Because something hasn't been proved true does not make it false.

This is known in all fields of inquiry as the "Argument from Ignorance." It is a fallacy of reason to claim that something is true only because it has not been proven false.

Only in String Theory, Divorce Court, and Sylvia Browne's mind is this fallacy considered a valid form of reason.

The use of the Argument from Ignorance automatically voids the assertion, rendering it a form of pseudo-science or "woo."

Therefore, I reject your argument.

-Fnord of Dyscordia-

 

[AmateurScientist]

Well, if it turned out that gravity was actually affected by interaction with other universes, that would certainly have implications for us here in our own universe.

How would we ever know?

AS

 

[AmateurScientist]

take away any multiverse reasoning, and by our current understanding, the universal big bang boundary conditions sufficient for our universe are ridiculously, astromically and stupendously unlikely.....

I think you have completely misunderstood the point of the anthropic principle. If any of those necessary conditions were not true, then either we wouldn't be here to note it, or "we" would be very different creatures in a very different time and place. In the cosmic scheme of things, our existence is inconsequential. Ten billion years ago our sun didn't exist, and neither did we. Do you think conditions looked so finely tuned for life back then? Indeed, the way our universe is ordered at the moment is inconsequential cosmically as well.

Our universe only looks finely tuned (which is of course a concept from Intelligent Design theory) because we are already here within it and looking back at it. If we didn't exist in it, but could somehow look at it objectively from outside it, it wouldn't look nearly so interesting without life. Sure, some really spectacular stuff goes on as a result of activity in and around stars, but another universe with different physical laws might be more or less spectacular. In any case, we'll never know because we cannot.

AS

 

[Orphia Nay]

Hi Wolfman.

You might remember me being fascinated at one stage by the multiverse theory. However, I learned several years ago that most of those theories were based on the "free lunch" fallacy that appeals to woos' fascination with "love and light".

This one's a bit different. Let me get this straight. Because gravity behaves the way we expect it to, some scientists think there are multiverses?

Argument from incredulity and non sequitur rolled into one.

 

[Apathia]

Warped Passages: Unraveling The Mysteries of The Universe's Hidden Dimensions by Lisa Randall

A nice read, full of woo love & light if that's all Theoretical Physics is anymore.

She's expecting the LHC (Large Hadron Collider) will provide smoking gun evidence of extradimensional effects.

 

[Schneibster]

Brian Greene discussed the idea that gravity might be so weak because its action occurs across different "brane worlds" near the end of The Fabric of the Cosmos. It's not woo; it's just speculative. It appears that the idea can be applied using other than string theory, too; being as how we see it being discussed here in the context of the Many Worlds interpretation of the Standard Model. So I think that suggesting it's woo is either premature, or disingenuous.

 

[Roboramma]

This is known in all fields of inquiry as the "Argument from Ignorance." It is a fallacy of reason to claim that something is true only because it has not been proven false.

It's also a falacy to attribute a position to someone that they don't hold.

No one said string theory is correct simply because it can't be proven false. Andyandy said that we can't say it's false because we can't prove it's false. There's a difference.
As for string theory - the fact that it hasn't yet made any testible predictions doesn't mean that it won't. I don't see how working on it to try to find those testible predictions is woo.

That doesn't mean I think it's the best way to spend valuable time and resources, but I don't see how you can call it woo.

 

[Roboramma]

Let me get this straight. Because gravity behaves the way we expect it to, some scientists think there are multiverses?

Argument from incredulity and non sequitur rolled into one.

I don't see that. How about this:
If all masses caused an attractive force that diminished as the square of the distance between them, we'd expect to see the following:
-Objects on earth fall at the same rate, regardless of their mass.
-Planetary motion following kepler's laws
We do see those things.
This is evidence for newton's universal gravitation.

If there are multiverses, we'd expect to see the following:
-gravitation working in some of the ways that we know it does.
It does work in those ways.
This is evidence for multiple universes.

Of course whether or not it's strong evidence, I know too little to say. You might argue that they constructed the theory to conform to the data. In which case it'd be nice if the theory had some falsifiable prediction that was outside of that data.

 

[Wolfman]

Hi Wolfman.

You might remember me being fascinated at one stage by the multiverse theory. However, I learned several years ago that most of those theories were based on the "free lunch" fallacy that appeals to woos' fascination with "love and light".

This one's a bit different. Let me get this straight. Because gravity behaves the way we expect it to, some scientists think there are multiverses?

Argument from incredulity and non sequitur rolled into one.

Orphia,

Ah, glad to finally have you join one of my threads! However, I think you've misunderstood the article (or my explanation of it).

"Gravity behaves the way we expect it to"...well, we "expect" it to act a certain way because we've observed it to act that way. It wasn't that long ago that we "expected" gravity to cause heavier objects to fall faster. It was observation and experimentation that caused us to change this view. That has nothing to do with the discussion at hand.

While physicists are good at prediction how gravity will behave, they have a much more difficult time explaining why it behaves that way...in particular, why gravity is so much weaker as a force than any of the other natural forces. This theory (whether you use multiple dimensions, or multiple universes) attempts to explain the 'why' of the question, not the 'how'.

 

[Schneibster]

If there are multiverses, we'd expect to see the following:
-gravitation working in some of the ways that we know it does.
It does work in those ways.

I'd interject that we'd also expect to see gravity be a very weak force, being so spread out, and it is.