Is gravity 'weak' because it leaks into higher dimensions?

[B.Spinoza]

I seem to have read something once that suggested that gravity may be leaking into other dimensions/branes, this could explain why this force is so weak.
I've been left thinking that it makes sense as a possibility. If it turns out to be the case, could Dark Energy then be leaked gravitational energy from other dimensions leaking into our Universe? I realize that Dark Energy has the opposite effect to gravity, but somehow I think that makes sense, just like when you move a figure from one side of an = sign to another, the sign flips.

Ideas anybody? Thanks

 

[Mark M]

I seem to have read something once that suggested that gravity may be leaking into other dimensions/branes, this could explain why this force is so weak.
I've been left thinking that it makes sense as a possibility. If it turns out to be the case, could Dark Energy then be leaked gravitational energy from other dimensions leaking into our Universe? I realize that Dark Energy has the opposite effect to gravity, but somehow I think that makes sense, just like when you move a figure from one side of an = sign to another, the sign flips.

Ideas anybody? Thanks

Hi B.Spinoza, welcome to the forum!

The idea you're speaking of comes out of non-perturbative string theory, called M-theory. In M-Theory, strings are not the only ingredient. Rather, multidimensional strings, called branes, are fundamental along with ordinary one dimensional strings. M-Theory explains string tension, the variable that determines string oscillations and hence particle values, can be explained in terms of how tightly the branes hold the ends of open strings, the strings that make up everything except gravity. Gravity, in string theory, is represented by a closed loop string. Since a brane cannot hold onto a closed loop, since it has no ends, it will occasionally float off of the brane.

The problem with supposing dark energy is truly gravity from other branes is it doesn't explain the constancy of the acceleration of the expansion of the universe. But I can't say for sure, considering M-theory is still in its infancy. I did a search on arxiv for a paper on the topic, but I couldn't find anything.

But, some string theorists have proposed that dark matter may be gravity from other branes.

The idea may be a source of experimental testing of M-Theory in the future. If particle collisions could produce less mass than was originally started with, that would be a sign of strings being 'knocked off' of our brane.

 

[B.Spinoza]

Hi Mark

Thanks for the welcome and reply. It all makes sense (so much as these things can)

re: 'doesn't explain the constancy of the acceleration of the expansion of the universe'... OK, but I thought that the Universe hasn't expanded constantly, I was under the impression that after 'inflation' the expansion slowed considerably and then kinda kept coasting on and that the expansion rate is actually increasing as the binding force of gravity is diluted throughout the increasing volume of the Universe.

If the Universe has a finite mass/energy and is a closed system (I know it wouldn't be if gravitational energy was leaking across branes) then the amount of gravitational energy that leaks out would be constant. The energy leaking into our Universe from other branes would be constant too as the other Universes have a finite/fixed mass, if that is the source of the Dark Energy and associated expansion then it would a constant force.

Is that convoluted b.s. or does it make sense?

 

[Mark M]

re: 'doesn't explain the constancy of the acceleration of the expansion of the universe'... OK, but I thought that the Universe hasn't expanded constantly, I was under the impression that after 'inflation' the expansion slowed considerably and then kinda kept coasting on and that the expansion rate is actually increasing as the binding force of gravity is diluted throughout the increasing volume of the Universe.

Remember, inflation was not caused by dark energy. Inflation occurred because a scalar field, known as the inflaton field, decayed into a false vacuum. A false vacuum is essentially a state that a field can get 'stuck' in, while trying to decay to it's ground state, a true vacuum. In order for the inflaton field to reach a true vacuum, it had to exert an enormous negative pressure, resulting in repulsive gravity. This repulsive gravity drove the expansion of the universe until the inflaton field decayed.

The rate of expansion is increasing, yes. But it is most likely doing so at a fixed rate. Once inflation ended, the universe underwent the normal expansion, decelerating over time. The gravity of the totality of everything in the universe out weighed that of dark energy, causing the universe to slow down over time. But as the volume of the universe diluted, dark energy began to have a more prominent role. About 7 billion years ago, the force of dark energy overcame that of gravity, and began to accelerate the expansion of the universe. The important point to remember is that, as far as we know, dark energy's value seems to remain constant, or at least, very close to it. It may lose some density through expansion, but nothing like the amount lost by matter/dark matter.

So, in short, yes, the universe is accelerating. But it is doing so according to a fixed rate. If gravitons from other branes were the case, we should see fluctuations in this rate of expansion, not a constant acceleration.

If the Universe has a finite mass/energy and is a closed system (I know it wouldn't be if gravitational energy was leaking across branes) then the amount of gravitational energy that leaks out would be constant. The energy leaking into our Universe from other branes would be constant too as the other Universes have a finite/fixed mass, if that is the source of the Dark Energy and associated expansion then it would a constant force.

Good point, but you are relying on the fact that the other branes are identical to ours. Say another brane came floating by through the bulk of space, and dropped off some repulsive gravitons. We would detect this as an abnormality in the rate of expansion.

 

[B.Spinoza]

Super. I like that answer, I need to read up for the first sentence a little; the rest made sense. I get the history of Universal expansion a little more, not that I can picture 7 billion.

I'm guessing 'Inflatons' are hypothetical particles that carry the inflation force? (a kinda anti-Higgs?) Anti-gravity? Maybe one day all this atom smashing will come up with something useful! ;-)

Branes shouldn't be symmetrical to ours, from what I understand that most of the concept relies on each brane having different qualities.

I'm going to keep thinking... thanks again.

 

[Mark M]

I'm guessing 'Inflatons' are hypothetical particles that carry the inflation force? (a kinda anti-Higgs?) Anti-gravity?

Exactly. Originally, when Alan Guth proposed inflation in the 1970's, he assumed that the Higgs Field played the role of the inflaton field. Later, with the dawn of new inflation pioneered by physicists such as Paul Steinhardt and Andrei Linde, it was realized the inflaton had to be its own particle.

There isn't an inflation force, but it is repulsive gravity. Here's how it works:

In general relativity, mass, energy, and pressure produce the attractive gravity that we are familiar with. This causes a positive curvature in spacetime. Negative pressure, the force that is exerted by a tense rubber band, has the opposite effect - it gives spacetime a hyperbolic shape, resulting in repulsive gravity. Since gravity is just the shape of spacetime, a negative pressure will drive expansion.

The inflaton field is a scalar field, meaning it takes a value at every point in space. Essentially, when it was trying to reach it's ground state, it super-cooled. This is similar to how purified water can be lowered below 0 degrees Celsius without freezing. The inflaton field would react by filling the universe with large amounts of energy, and as Guth found, a negative pressure. This enormous negative pressure would allow for the inflaton field to reach its true vacuum, and in the process, expand the universe by a huge amount. After reaching this ground state, it would decay into a hot bath of radiation, which would soon give birth to the matter in the universe.

 

[Chronos]

Gravity leaking into other dimensions is not a satisfying solution. Were this true, should we not expect gravity from 'other universes' to leak into our universe?

 

[rbj]

gravity is neither weak nor strong in comparison to, say, EM because it acts on mass while EM acts on charge and the two quantities are incommensurable, so they cannot be directly compared. it is true that the attractive gravitational force between two protons is much much less than the electrostatic repulsive force between the same two protons (both fields are inverse-square, so it doesn't matter what the spacing is), and that is because the charge on the protons is in the same ballpark as the Planck charge, but the mass of the protons is far, far less than the Planck mass.

quoting Frank Wilczek:

...We see that the question [posed] is not, "Why is gravity so feeble?" but rather, "Why is the proton's mass so small?" For in Natural (Planck) Units, the strength of gravity simply is what it is, a primary quantity, while the proton's mass is the tiny number [1/(13 quintillion)]...

 

[Chronos]

er, and your point is ...

 

[Dickfore]

This is from Anthony Zee's "QFT in a Nutshell", chapter I.6.

In a $D = (3 + n)$-dimensional world, the potential energy goes as:
$$V(r) \propto \int{d^{3 + n} k \, \frac{e^{i \mathbf{k} \cdot \mathbf{x}}}{k^2}} \propto \frac{1}{r^{1 + n}}$$
If the gravitational force is proportional to the masses of the interacting particles regardless of the number of spatial dimensions, we may write:
$$V(r) = G_{3 + n + 1} \, \frac{m_1 \, m_2}{r^{1 + n}}$$

In natural units ($\hbar = c = 1$), the dimensions of mass, length, and time satisfy $\mathrm{T} = \mathrm{L} = \mathrm{M}^{-1}$, and every physical quantity has only a mass dimension. For example:
$$\left[ V(r) \right] = [E] = \mathrm{M} \, \mathrm{L}^2 \, \mathrm{T}^{-2} \stackrel{\mathrm{n.u.}}{\rightarrow} \mathrm{M}$$
Then, the "Universal Gravitational Constant" in $3 + n + 1$ space-time dimensions has a mass dimension:
$$\left[ G_{3 + n + 1}\right] = \frac{[E] \, [r]^{1 + n}}{[m]^2} = \mathrm{M}^{-2 - n}$$
Indeed, this constant defines a Planck mass in $3 + n + 1$ space-time dimensions:
$$G_{3 + n + 1} = \frac{1}{M_{\mathrm{Pl}, 2 + n}}$$
Indeed, in (3 + 1)-space-time, $M_{\mathrm{Pl},4} = 1/\sqrt{G_{4}} \sim 10^{19} \, \mathrm{GeV}$. This is a HUGE energy scale (energy and mass have the same dimension in natural units), a fact we interpret as the reason why gravity is so weak.

But, suppose the extra n spatial dimensions are "curled up" to linear dimensions of the size R. This need not be a microscopic length scale, but is small enough that it had not been detected by gravitational experiments performed on such a small length scale. For distances $r \gg R$, the gravitational flux spreads only in the 3 unfolded linear dimensions, and the gravitational potential energy goes as:
$$V(r) = \frac{m_1 \, m_2}{M^{2 + n}_{\mathrm{Pl}, 3 + n +1}} \, \frac{1}{R^n} \, \frac{1}{r}$$
If we interpret:
$$\frac{1}{M^2_{\mathrm{Pl},4}} \equiv \frac{1}{M^{2 + n}_{\mathrm{Pl}, 3 + n +1} R^{n}}$$
$$\frac{M_{\mathrm{Pl},4}}{M_{\mathrm{Pl},3 + n + 1}} = \left( M_{\mathrm{Pl},3 + n + 1} R \right)^\frac{n}{2}$$

Now, the Planck mass in $3 + n + 1$ space-time dimensions may as well be of the order of magnitude of ordinary particle masses (let us choose a range of values 10 eV - 100 GeV). This would put the dimensioless ratio of masses:
$$\frac{M_{\mathrm{Pl}, 4}}{M_{\mathrm{Pl}, 3 + n + 1}} = 10^{17} - 10^{27}$$
Then, the distance R, should be:
$$R = \frac{1}{M_{\mathrm{Pl},3 + n + 1}} \, \left( \frac{M_{\mathrm{Pl}, 4}}{M_{\mathrm{Pl}, 3 + n + 1}} \right)^\frac{2}{n} = \frac{1}{M_{\mathrm{Pl}, 4}} \, \left( \frac{M_{\mathrm{Pl}, 4}}{M_{\mathrm{Pl}, 3 + n + 1}} \right)^{1 + \frac{2}{n}}$$
This is a monotonically rising function of the dimensionless ratio (the smaller the mass of the Planck particle, the bigger the ratio). For a popular choice $n = 6$, we would have:
$$R = (10^{19} - 10^{31}) \, M^{-1}_{\mathrm{Pl},4} = (10^{-16} - 10^{-4}) \, \mathrm{m}$$

 

[Physgeek123]

Dangit People! What inflation really was.

Remember, inflation was not caused by dark energy. Inflation occurred because a scalar field, known as the inflaton field, decayed into a false vacuum. A false vacuum is essentially a state that a field can get 'stuck' in, while trying to decay to it's ground state, a true vacuum. In order for the inflaton field to reach a true vacuum, it had to exert an enormous negative pressure, resulting in repulsive gravity. This repulsive gravity drove the expansion of the universe until the inflaton field decayed.

THIS AND EVERYTHING ELSE can be explained by the standard model if you look a little closer. Problem?

It goes like this: After a fraction of a second after the big bang (brane collision, whatever) there were only TWO fundamental forces instead of four. They were the Electromagetism force and the Weak-nuclear force. The amalgam of these two forces formed the Electro-weak force.

This is the "inflaton" field you speak about (apparently). Anyway back to the Big Bang timeline, this super-force somehow caused inflation, spreading and recycling (yes recycling not creating as stated by E=mc^2) matter in an incredibly short amount of time. We now call this inflation.

But why do we not see the super weak force now? Think of each force as a spinner with two outputs. When you spin the spinner, it gains energy and then soon it looses it and lands on one of the possible outputs. Now apply that to the electro-weak force. It had a MASSIVE effect and quickly exhausted it's available energy thus forcing the spinner to land on something. But unlike spinners in real life, forces (when they stop "spinning") land on all the outcomes at the same time. The electro-weak superforce has now split into The Weak nuclear force, the strong nuclear force and the Electromagnetic force. But where's gravity?

Scientists believe that gravity was the result of the same superforce which spawned dark energy. The balancing scale of gravity vs. dark energy was tipping toward gravity and then for some reason reversed giving dark energy the upper hand.

So the answer to the question "Is gravity 'weak' because it leaks into higher dimensions?" is a big no no. Gravity is the same thing as everything else. It just seems to be weaker because there is not much concentration and quantity of the things it has control over (matter).

Hope that helped.

- Physgeek123

 

[rbj]

er, and your point is ...

dunno whom you were addressing, but if it was me, the point is that the premise of "weak gravity" that the question of this thread is based on is flawed. gravity is not weak, but protons (and other elementary particles) have very, very small mass, while their charge (if they are not neutral) is not particularly small. it is because of this fact that it appears to some that gravity is weak but they are considering the wrong quantities.

 

[Mark M]

Gravity leaking into other dimensions is not a satisfying solution. Were this true, should we not expect gravity from 'other universes' to leak into our universe?

An idea in brane cosmology is that dark matter is composed of gravitons from other branes. This would explain why it's proved difficult to find it's constituents. Since the prospect of two 3-branes hovering near each other in a ten dimensional space seem slim to none, it would be unlikely that we would get a steady flow from these other branes.

As usual with all cosmological models based off of M-theory, it's interesting, but there is no evidence.

It goes like this: After a fraction of a second after the big bang (brane collision, whatever) there were only TWO fundamental forces instead of four. They were the Electromagetism force and the Weak-nuclear force. The amalgam of these two forces formed the Electro-weak force.

This is incorrect. A grand unified theory supposes that there was one unified forces, which then broke symmetry when the Higgs mechanism was activated.

This is the "inflaton" field you speak about (apparently). Anyway back to the Big Bang timeline, this super-force somehow caused inflation, spreading and recycling (yes recycling not creating as stated by E=mc^2) matter in an incredibly short amount of time. We now call this inflation.

Also incorrect. Grand unified theories do not claim any role in inflation, that is the sole purpose of the inflaton field. I suggest you do some research on inflation, that's not how it occurs. You should read this:

http://arxiv.org/abs/astro-ph/0101507

But why do we not see the super weak force now? Think of each force as a spinner with two outputs. When you spin the spinner, it gains energy and then soon it looses it and lands on one of the possible outputs. Now apply that to the electro-weak force. It had a MASSIVE effect and quickly exhausted it's available energy thus forcing the spinner to land on something. But unlike spinners in real life, forces (when they stop "spinning") land on all the outcomes at the same time. The electro-weak superforce has now split into The Weak nuclear force, the strong nuclear force and the Electromagnetic force. But where's gravity?

I don't know where you got this information. The breaking of symmetry of the forces was caused by the Higgs field. Once again, read this:

http://en.wikipedia.org/wiki/Higgs_mechanism

Scientists believe that gravity was the result of the same superforce which spawned dark energy. The balancing scale of gravity vs. dark energy was tipping toward gravity and then for some reason reversed giving dark energy the upper hand.

Gravity is not a force. It is a curvature in spacetime, altering the geodesic of objects traveling through it. No scientist believes in a 'superforce' that spawned it, it is an intrinsic property of spacetime.

So the answer to the question "Is gravity 'weak' because it leaks into higher dimensions?" is a big no no. Gravity is the same thing as everything else. It just seems to be weaker because there is not much concentration and quantity of the things it has control over (matter).

Once again, you're mistaken. Gravity is not the same. Gravity is not a force.

Great post DF, that would seem to solve the problem better than gravitons 'leaking' off of our brane.

 

[alexg]

Gravity leaking into other dimensions is not a satisfying solution. Were this true, should we not expect gravity from 'other universes' to leak into our universe?

The idea is not that there are 'other universes'. It's that unlike electroweak and strong force, gravity is able to propagate into the additional dimensions called for by M-theory. All those dimensions are part of our universe, but only gravity can move in those 'directions'. It would explain why gravity is so weak relative to the other forces. It's diluted through out the other 10 dimensions.

 

[DaveC426913]

you can get a warning for posting crazy links even in jest

That wasn't in jest. Crackpottery and crackpottery link reported. And he may get more than just a warning.

 

[TheTechNoir]

The idea may be a source of experimental testing of M-Theory in the future. If particle collisions could produce less mass than was originally started with, that would be a sign of strings being 'knocked off' of our brane.

Also if I remember correctly another way of possibly testing both the gravity leaking into other dimensions hypothesis as well as the upper limit of and the actual size of the extra dimensions is by testing gravity on smaller and smaller scales and seeing if it's strength suddenly increases. If for example we were able to test gravity's strength at a scale of 0.001 mm and it was the same, we'd know that the extra dimensions must be smaller than that if the idea is correct. And of course if we found gravity suddenly increased at x size scale then that would be one explanation, it was leaking off into the tiny dimensions, ones that we were detecting the signature of.

 

[B.Spinoza]

The idea is not that there are 'other universes'. It's that unlike electroweak and strong force, gravity is able to propagate into the additional dimensions called for by M-theory. All those dimensions are part of our universe, but only gravity can move in those 'directions'. It would explain why gravity is so weak relative to the other forces. It's diluted through out the other 10 dimensions.

Yeah, what he said is the kind of concept that spawned my initial question.

Interesting answers all.

 

[B.Spinoza]

Gravity leaking into other dimensions is not a satisfying solution. Were this true, should we not expect gravity from 'other universes' to leak into our universe?

Yes. I suggested that Dark Energy may be gravity leaking in. Its all guessing...

 

[TheTechNoir]

Although that makes no sense, as was already pointed out it has a far far far far greater likelihood of explaining dark matter than dark energy. And even for dark matter it's 100% speculation.

 

[B.Spinoza]

Although that makes no sense, as was already pointed out it has a far far far far greater likelihood of explaining dark matter than dark energy. And even for dark matter it's 100% speculation.

Was that directed at my previous?

Dark Matter is unlikely to be gravity leaking in from other dimensions or similar. Dark Matter is lumpy in its Universal distribution, it is clustered around matter.

Dark Energy seems to come from space as a whole.

Why would it make no sense that gravity leaks? If gravity leaks out from our Universe/brane/whatever then maybe it leaks in from other places too?

It is all 100% speculation. We know something out there is making the Universe expand and that there is more gravity than can be accounted for from the observable matter. 'We' hope there is a Higgs particle and that this is Dark Matter. Correct me if I'm wrong, but I don't think there is much else to it? It really is a true unknown, something very exciting in this age of science.

 

[TheTechNoir]

Yes it was directed at your previous and Mark M already explained this to you in-depth in the opening posts of this thread and you responded to them as well ...

Dark Matter clusters around matter? I think it's a lot more likely that matter clusters around dark matter considering how much more gravity dark matter accounts for than mass. Also that inconsistent universal distribution would probably increase the likelihood of it explaining dark matter as opposed to dark energy.I never said it made no sense that gravity leaks into our universe. I don't firmly believe it does, but I don't have any reason to think it doesn't either. I said it doesn't make sense that gravity from another brane(s) is the cause of our universe's constant repulsive acceleration.

Please explain to me reasons why gravitons from another brane is more realistic at explaining dark energy than dark matter. I can't think of a single reason.

 

[TheTechNoir]

We know something out there is making the Universe expand and that there is more gravity than can be accounted for from the observable matter. 'We' hope there is a Higgs particle and that this is Dark Matter. Correct me if I'm wrong, but I don't think there is much else to it? It really is a true unknown, something very exciting in this age of science.

I fail to see what the first half of your first sentence and the second half have to do with each other. You make a statement about dark energy then one about dark matter, follow it with an inaccurate assessment of dark matter then conclude that, that is the whole story.

There isn't much else to what? You're talking about dark energy and dark matter, so yes there is a lot more to those distinct things than a suggested particle identity for dark matter.

 

[Mark M]

Was that directed at my previous?

Dark Matter is unlikely to be gravity leaking in from other dimensions or similar. Dark Matter is lumpy in its Universal distribution, it is clustered around matter.

Dark Energy seems to come from space as a whole.

Why would it make no sense that gravity leaks? If gravity leaks out from our Universe/brane/whatever then maybe it leaks in from other places too?

It is all 100% speculation. We know something out there is making the Universe expand and that there is more gravity than can be accounted for from the observable matter. 'We' hope there is a Higgs particle and that this is Dark Matter. Correct me if I'm wrong, but I don't think there is much else to it? It really is a true unknown, something very exciting in this age of science.

Dark matter is the same animal as regular matter, the only difference being that it does not interact with the electromagnetic force. Also, dark matter is something else entirely, it has nothing to do with the Higgs Field.

Please explain to me reasons why gravitons from another brane is more realistic at explaining dark energy than dark matter. I can't think of a single reason.

TheTechNoir, dark matter and dark energy are different phenomena. As I explained to B. Spinoza, dark matter is very similar to matter. Dark energy, on the other hand, is the energy of space itself. It may be a cosmological constant, or the quintessence predicted by quantum mechanics, or something else entirely.

 

[TheTechNoir]

Thanks for that follow-up post, I was completely perplexed when he made that suggestion that it could explain dark energy and you explained thoroughly why it is such an unlikely idea (an explanation he seemed to understand) and made the off-hand point how it has however been proposed as the cause of dark matter observations. Then he later makes a post seemingly having back-wheeled to his original misguided idea as if the conversation never even happened.

And I am aware that the only similarity between the two phenomenon is the first word intended non-scientifically in their names. Thanks mate

 

[B.Spinoza]

"Dark Matter clusters around matter? I think it's a lot more likely that matter clusters around dark matter considering how much more gravity dark matter accounts for than mass." I agree, I could have worded it better. I was thinking of some of the visualisations of the Universe that I have seen and the cloud of dark matter around the visible.


"Also that inconsistent universal distribution would probably increase the likelihood of it explaining dark matter as opposed to dark energy." Cool, please explain further, that is interesting.


"I never said it made no sense that gravity leaks into our universe. I don't firmly believe it does, but I don't have any reason to think it doesn't either." agreed, me neither. I just wondered what people thought.


"I said it doesn't make sense that gravity from another brane(s) is the cause of our universe's constant repulsive acceleration." I meekly suggested that is is possible that the inward leaking gravity would be opposite to G and thus the force of expansion. Could the polarisation/charge whatever of the field have a reverse effect in a different dimension/brane whatever.

"Please explain to me reasons why gravitons from another brane is more realistic at explaining dark energy than dark matter. I can't think of a single reason."

I don't get this, dark energy has nothing to do with dark matter apart from 4 letters and that nobody seems to know what they are yet.

I'm just curious, apologies if not smart enough for the forum.

 

[TheTechNoir]

"Also that inconsistent universal distribution would probably increase the likelihood of it explaining dark matter as opposed to dark energy." Cool, please explain further, that is interesting.


"I never said it made no sense that gravity leaks into our universe. I don't firmly believe it does, but I don't have any reason to think it doesn't either." agreed, me neither. I just wondered what people thought.


"I said it doesn't make sense that gravity from another brane(s) is the cause of our universe's constant repulsive acceleration." I meekly suggested that is is possible that the inward leaking gravity would be opposite to G and thus the force of expansion. Could the polarisation/charge whatever of the field have a reverse effect in a different dimension/brane whatever.

"Please explain to me reasons why gravitons from another brane is more realistic at explaining dark energy than dark matter. I can't think of a single reason."

I don't get this, dark energy has nothing to do with dark matter apart from 4 letters and that nobody seems to know what they are yet.

I'm just curious, apologies if not smart enough for the forum.

There's nothing to explain further for that first quote, it's already been thoroughly explained. An exert of that:

So, in short, yes, the universe is accelerating. But it is doing so according to a fixed rate. If gravitons from other branes were the case, we should see fluctuations in this rate of expansion, not a constant acceleration.


Good point, but you are relying on the fact that the other branes are identical to ours. Say another brane came floating by through the bulk of space, and dropped off some repulsive gravitons. We would detect this as an abnormality in the rate of expansion.

An idea in brane cosmology is that dark matter is composed of gravitons from other branes. This would explain why it's proved difficult to find it's constituents. Since the prospect of two 3-branes hovering near each other in a ten dimensional space seem slim to none, it would be unlikely that we would get a steady flow from these other branes.

Though purely speculative, people would be almost universally agreed with this as more likely than the other. There is a reason why you can find articles and research on gravity leaking into our universe from other branes being responsible for what we see as dark matter and none regarding it explaining dark energy. M-Theory is purely speculative and incomplete, but based on what we do know about it, the probability of perfectly or near perfectly uniform distribution of gravitons into our universe in a repulsive manner is less likely than an unsteady flow of gravitons in different areas causing an attractive (positive gravitational) influence. We're just going with likelihoods here, you could very well be right but I think almost anyone would disagree with you in suggesting that it is a more likely explanation of dark energy than dark matter.

I understand that was what you were proposing as an idea, and there's nothing wrong with that. I may have misunderstood your intent with re-posting that you'd already posed that question as if you had reason to believe or support it when it was already shown to be most probably debunked. I posted my original responses at 12+ hours into a night shift at work, interpretation not the best.

Again I'm well aware that the two have nothing to do with. They are just two things that have been talked about in this thread, you posed the idea of one being the cause of gravity leaking into our universe from other branes while suggesting that the other is unlikely caused by the leaking of gravity into our universe from other branes

"Dark Matter is unlikely to be gravity leaking in from other dimensions or similar. Dark Matter is lumpy in its Universal distribution, it is clustered around matter."

I am merely stating that it is the other way around. It is an accepted idea (with no really notable backing for or against it to my knowledge, though it isn't a leading theory) that dark matter may be caused by this mechanism whereas it is not an idea taken seriously by anyone again to my knowledge that dark energy is caused by this mechanism. Basing off of what little we 'know' of m-theory and dark matter it seems a more realistic or likely fit than with dark energy.

I know that dark matter & dark energy have absolutely nothing to do with each other. I am disagreeing with you dispelling one as unlikely while posing the possibility of the other. My post wasn't meant to come across rudely, it probably did and my apologies. I was just perplexed by your second page post as it was already explained to you by someone who knows a lot more than both of us regarding all concerned subjects that it's one of the dark matter candidates and doesn't seem to be as likely as an explanation for dark energy and as he said there is nothing on the arxiv about it either. I think that the broader scientific community would agree with this too. Hope I explained this alright.

 

[skeptic2]

I seem to have read something once that suggested that gravity may be leaking into other dimensions/branes, this could explain why this force is so weak.

If gravity were leaking into or out of our universe in quantities great enough to explain why gravity is a weak force, then surely it surely would have been detectable as a violation of the inverse square law.

 

[B.Spinoza]

Thanks all. I shall no-longer ponder a Universe with leaky G.

Have a good weekend.

 

[Mark M]

If gravity were leaking into or out of our universe in quantities great enough to explain why gravity is a weak force, then surely it surely would have been detectable as a violation of the inverse square law.

Skeptic, if the radii of the extra dimensions were small enough, the break from the inverse sqaure law would be noticeable at microscopic distances far out of the reach of our particle accelerators, and at very high energy levels.

 

[skeptic2]

I'm afraid I don't understand your response. The OP's original question suggested that the reason gravity is so much weaker than the other forces might be that it may be leaking into other dimensions. In as much as the inverse square law is a direct consequence of propagation in three dimensions it should be obvious that propagation into additional dimensions to any significant amount would have to increase the value of the propagation exponent.

The size of the radius of the extra dimensions really doesn't come into play here. If enough gravity is leaking into other dimensions to reduce gravity from a strong force to a weak force, it really doesn't matter how small the radii of the other dimensions are, it will have to noticeably increase the propagation exponent.

 

[Mark M]

I'm afraid I don't understand your response. The OP's original question suggested that the reason gravity is so much weaker than the other forces might be that it may be leaking into other dimensions. In as much as the inverse square law is a direct consequence of propagation in three dimensions it should be obvious that propagation into additional dimensions to any significant amount would have to increase the value of the propagation exponent.

The size of the radius of the extra dimensions really doesn't come into play here. If enough gravity is leaking into other dimensions to reduce gravity from a strong force to a weak force, it really doesn't matter how small the radii of the other dimensions are, it will have to noticeably increase the propagation exponent.

Skeptic, the point I was trying to make was that if extra dimensions were curled up and small - as results from particle accelerators would require them to be - they would have no effect on gravitational force, and hence would not be an explanation of a weak gravitational force.

The idea of extra dimensions being responsible for weak gravity in M-theory, as I explained in my original discussion with OP, isn't that the presence of the extra dimensions has any effect on gravity - it's that gravitons would 'leak' off of our D3-brane. This would result in a lower Newton's constant, with no effect on the inverse square law.

Sorry if I was unclear about this in my response.

 

[TheTechNoir]

Skeptic, the point I was trying to make was that if extra dimensions were curled up and small - as results from particle accelerators would require them to be - they would have no effect on gravitational force, and hence would not be an explanation of a weak gravitational force.

The idea of extra dimensions being responsible for weak gravity in M-theory, as I explained in my original discussion with OP, isn't that the presence of the extra dimensions has any effect on gravity - it's that gravitons would 'leak' off of our D3-brane. This would result in a lower Newton's constant, with no effect on the inverse square law.

Sorry if I was unclear about this in my response.

Skeptic: this is what I was referring to in the first page. It's an interesting consequence of this, that if we probed gravity's strength on smaller and smaller distance scales and eventually found a distance at which it was stronger, we would under this belief have evidence towards the size of the small dimensions. Likewise the smaller distances we probe without finding any deviation is evidence suggesting if the dimensions exist, they must be smaller than that amount that we probed and saw no change in gravity's strength at.

 

[tanzanos]

Perhaps gravity is but a shadow cast by the interactions of the remainder forces. We can feel the effects and even measure it but like a real shadow; It has no substance. Perhaps we should rename gravity into "Space curvature". Like any curvature it is not a force in itself but the result of the effects of other forces. Just a thought!