Einstein + Hawking = Dark Matter ?

[gutemine]

Hi !

I'm trying to understand the Dark matter problem, because it scares me if clever people tell me they don't know out of what 23% of the universum is consisting.

But let's start with a simple question on GR:

GR is stating that a body moving at a speed close to c holds an almost infinite energy.

For explaining this Einstein introduced the relativistic mass which becomes infinite at c.

But if mass produces gravitation by curving the space time continuum, wouldn't this mean that because of this increasing mass/gravitation at a point BEFORE c already the body would collapse and become a black hole at a pretty high speed ?

Even a very small mass (for a example a proton) flying close to c would then become a micro black hole invisible to the universum = Dark matter ?

Probably for such a small particel we would need quantum physics and not GR, but
if our understanding of black holes would still apply to such a micro black hole, wouldn't this mean that there would be Hawking radiation until it slows down and reappears when the velocity energy is eaten up after quite some time ?

This leads to the next question: If the big bang really was a kind of explosion, wouldn't this suggest that the outer most masses had the maximum possible speed ?

If these particles would then hold almost infinite energy at almost c, wouldn't they instantly become such micro black holes and stay at the forefront of the expansion of the universum, until their energy eats up and they re-appear after quite some time ? And couldn't this then be what we call Dark matter (because of the black hole effect beeing invisible) and continuously emmitting background radiation and continuously produce reappearing matter (=universum still giving birth) ?

And finally couldn't this mean that the acutal Dark matter of 23% is a very small portion of the original mass of the universum simply at very high speed - so in reality we are not missing that much because it is really more a kind of Dark Energy ?

Please enlight me ?

gutemine

 

[Ich]

You're not the first to ask this question.
Short answer: according to the relativity principle, the "fast moving" particle cannot know whether it is moving or the rest of the universe. Thus, it follows directly that neither the particle nor the universe can collapse due to velocity. You don't have to know the details to reach this conclusion.
Detail: the source of gravity is not mass or relativistic mass or energy, it is http://en.wikipedia.org/wiki/Stress-energy_tensor" that behaves properly.

And finally couldn't this mean that the acutal Dark matter of 23% is a very small portion of the original mass of the universum simply at very high speed - so in reality we are not missing that much because it is really more a kind of Dark Energy ?

No. We know from observations that DM must be cold, i.e. have negligible kinetic energy. If it were hot, it wouldn't collapse to build the large-scale structures we see, and its time evolution would be different.

 

[gutemine]

Hi !

Thanks for the quick reply and the pointers for helping me to 'understand' this.

I was not sure about this collapsing problem, because this seemed a little bit strange that everything would be smashed before reaching the speed of light.

Regarding the DM beeing identified as cold - how do we know this?

Because besides the Hawking radiation a BH cann't emmit anything - so it would be also 'cold' ?

And wouldn't it be the other way around - if it slows down it would 're-appear' ?

PS: was this already tried - eg use a particle accelerator to increase a particle close to c and measure the gravitation changes/effects ? Or is this not possible because due to the increased relativistic mass it is not possible to keep the particle circling when approaching c ?

gutemine

 

[Ich]

Regarding the DM beeing identified as cold - how do we know this?

Because besides the Hawking radiation a BH cann't emmit anything - so it would be also 'cold' ?

"Cold" means that the individual particles have not very much random velocity. Like the temperature of a gas cloud. It doesn't say anything about a temperature of a single particle (which does not exist, except for the BH).
If DM were hot, the haloes around galaxies would quickly evaporate if they were hot. To to mention that they wouldn't have formed in the first place.

was this already tried - eg use a particle accelerator to increase a particle close to c and measure the gravitation changes/effects ?

No. EM is some 10^40 stronger than gravity, you have no chance to detect such an effect.

 

[proteus13]

Anyone ever considered gravity to be non-linear but exponential in nature? I mean being rather weak over large distances, but getting exponentially stronger at planks length distances?

 

[hadsed]

Anyone ever considered gravity to be non-linear but exponential in nature? I mean being rather weak over large distances, but getting exponentially stronger at planks length distances?

This is Newtonian gravity...

 

[John232]

I was wondering if there was anyone who worked in astronomy that knows if after they measure the mass of a system from the orbits of nearby bodies if they then add a relative mass due to its relative speed to Earth. I was thinking that like spacetime dilation that the mass increase may only be detected by the object that it was in relative motion with. Also, I never read anything that stated that astronomers have found galaxies in space that have undergone some type of relativistic effects even when some near the edge of the visable universe travel close to the speed of light. It seemed like to me that just considering the apparent mass wouldn't be enough since it could appear to be more massive to an object with a relative velocity. Relative to the galaxies on the edge of the visable universe we are traveling close to the speed of light right now, and I am haveing no more trouble accelerating...

 

[twofish-quant]

GR is stating that a body moving at a speed close to c holds an almost infinite energy.

No it doesn't. There was a textbook by Gamov in the 1950's that tried to explain relativity by saying that things increase in energy and mass as they get closer to the speed of light, but that's really a very bad way of thinking about it, since it leads to all sorts of confusions like it one that you've gotten into.

For explaining this Einstein introduced the relativistic mass which becomes infinite at c.

And relativistic mass is really a bad concept that people nowadays don't use anymore. Because...

But if mass produces gravitation by curving the space time continuum, wouldn't this mean that because of this increasing mass/gravitation at a point BEFORE c already the body would collapse and become a black hole at a pretty high speed ?

Once you start thinking about objects moving near the speed of light as "increasing mass" then you start thinking that happens, when it doesn't.

 

[twofish-quant]

I was wondering if there was anyone who worked in astronomy that knows if after they measure the mass of a system from the orbits of nearby bodies if they then add a relative mass due to its relative speed to Earth.

People do take into account relativity when doing calculations of objects in the solar system. However, "relativistic mass" is such as bad way of thinking about what is going on, that no one uses it.

Also, I never read anything that stated that astronomers have found galaxies in space that have undergone some type of relativistic effects even when some near the edge of the visible universe travel close to the speed of light.

People don't mention it because to astrophysicists, relativity is like the sun shining or the Earth turning. It's such a big and obvious effect that pops up in so many places that people don't bother mentioning it.

 

[twofish-quant]

Anyone ever considered gravity to be non-linear but exponential in nature? I mean being rather weak over large distances, but getting exponentially stronger at planks length distances?

Yes.

 

[gutemine]

"Cold" means that the individual particles have not very much random velocity. Like the temperature of a gas cloud. It doesn't say anything about a temperature of a single particle (which does not exist, except for the BH).
If DM were hot, the haloes around galaxies would quickly evaporate if they were hot. To to mention that they wouldn't have formed in the first place.

No. EM is some 10^40 stronger than gravity, you have no chance to detect such an effect.

Thanks for the explanation. But I'm not sure if this is a correct assumption. Temperature in general gas theorie is defined as the summ of the energy of the random moves of the gas molecules. I agree that a similar concept can be applied to plain subatomic particles. BUT if all particles are moving quite fast in the same direction away from the observer this would NOT be temperature anymore (=cold). And this is ecactly what the forfront of the particles of a big bang would do. Only over time they maybe would still collide (flying not 100" parralell because of colissions and mass/gravitational effects) and hence slow down and become detected due to radiation. So the question is again if such fast moving particles would be detectable or could be the missing Dark matter.

And I disagree that relativistic mass is a bad concept. If the product of mass and speed² = Energy and I can detect only the energy because of the classic observer problem that you already mentioned then we cann't simply decide that because it needs so much more energy to accelerate because of getting closer to c the mass is not the one 'increasing' relatively to the observer.

And as your reply suggests it would be hard to find out who is right by doing experiments.

PS: Sorry for asking nasty questions, but as I originally said - the Dark Matter question could be either really a different matter (hard to accept a kind of divine glue for the universum) or a simple detectability problem.

gutemine

 

[Ich]

BUT if all particles are moving quite fast in the same direction away from the observer this would NOT be temperature anymore (=cold).

Right.

And this is ecactly what the forfront of the particles of a big bang would do.

I think there is a misconception. If you want to think of the BB as an explosion that throws some initial things very fast through space (which is rather wrong), there is still the fact that if the forefront of particles is here now, and we are here now, we and the particles must have the same average velocity. We're also the forefront.

If the product of mass and speed² = Energy

If so, we have two different symbols for essentially the same thing: m and E both denote energy then, which becomes especially clear if you adopt the usual convention of setting c=1 in relativity. So instead of wasting a symbol, we use m for rest mass, E for energy, and don't use relativistic mass, which is energy anyway.

 

[John232]

People do take into account relativity when doing calculations of objects in the solar system. However, "relativistic mass" is such as bad way of thinking about what is going on, that no one uses it.



People don't mention it because to astrophysicists, relativity is like the sun shining or the Earth turning. It's such a big and obvious effect that pops up in so many places that people don't bother mentioning it.

I had a really hard time accepting dark matter when I first heard about it, and you are not helping me much in thinking there is real dark matter out there. You make it sound like it is okay to ignore any relativistic mass when doing astrophysics and then just add some type of exotic matter to make up for it.

I have thought if say something like a nuclear reactor was seen by an observer traveling close to the speed of light then the mass along with the energy increase due to the increase of mass of the uranium in the reactor would allow it to be seen to function correctly to the observer traveling close to the speed of light. The particles would have an increase of mass from their perspectice so then it would have an equevelant increase in energy due to it. I don't think E=mc^2 would be true except when observed traveling at high relative speed. Since it comes from relative mass increase in own derivation, right?

I thought maybe relative mass wasn't correctly addressed. I saw an advisor post on this sight that the mass increase due to traveling at a higher velocity will not cause them to not accelerate at a normal rate or something to that effect, but when I learned about it in school that was the reason why an object couldn't travel the speed of light because their mass would be infinite and you can't accelerate an infinite mass.

What if the infinite mass was the uranium in a nuclear reactor? Wouldn't it put off infinite energy from the perspective of someone traveling close to the speed of light? Then at the same time people on Earth observe the reactor to have a normal amount of energy since they measure the uranium to have the same mass since they are not traveling a relative speed to it?

I think somehow relativistic mass would have to work out like the other relativistic effects since even though there are objects in the universe traveling at a high relative speed that we would have to still remain completely unaware of its effects since we never see them on a daily basis. Every experiment done on Earth has already been done with an object in space traveling at a highe relative speed, so then they should all get the same results. I think relative to the object traveling near the speed of light everything would look differently but the cause and effects of scientific principals should work the same way. So for instance if they observe a relativistic object with increased mass then there would be an increased energy from that mass so that the mass would be effected the same from that energy so that it is manipulated in the same fashion by it. So one frame of reference doesn't end up observing the same energy propeling a mass a shorter distance in one frame than an another. It would be the only way they would be able to agree on any reactions.

I think it is important to find out if galaxies traveling close to the speed of light have a relativistic mass to object they are traveling close to the speed of light relative too even though they don't appear to have an increase in mass relative to other systems traveling at a close speed to them. It has been said that they can travel faster than the speed of light as long as it is with the expansion of the space in the universe. I think it would be prudent to find if they are affected by spacetime dilation and mass increase when traveling along with the expansion of space, because then the assumption that we are traveling at a relativistic speed relative to something already with no observable affects on ourselves would be false.