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Have physicists discovered dark matter ?


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38 replies to this topic

#31    sepulchrave

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Posted 21 February 2013 - 09:45 PM

View Postkeithisco, on 21 February 2013 - 07:38 PM, said:

You are claiming that Gravity is a "Force" not a consequence of Einsteinian Spacetime curvature?
Gravity clearly is a force. Whether it is frame dependent or not is a different question.

View Postkeithisco, on 21 February 2013 - 07:38 PM, said:

Let me ask you a question: what is the speed of propagation of the Gravitic Force,
That depends on the medium. In a non-polarized vacuum it is be the speed of light.

View Postkeithisco, on 21 February 2013 - 07:38 PM, said:

over what distance would you expect attenuation of this force,
Any finite distance should give finite attenuation, just like all forces from finite sources.

In a dispersionless, sourceless, unpolarized medium the force attenuation law is r-2, where r is the distance from the source.

View Postkeithisco, on 21 February 2013 - 07:38 PM, said:

what is the Scaling of this force relative to Inertia?
It seems to be one-to-one.

View Postkeithisco, on 21 February 2013 - 07:38 PM, said:

You give me an Einstein thought experiment (maybe the Elevator accelerating away from the Earth at relativistic speed), and I will show you where it is inconsistent within its own F.O.R
You mean this one? Then OK, please proceed.


#32    keithisco

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Posted 25 February 2013 - 04:02 PM

View Postsepulchrave, on 21 February 2013 - 09:45 PM, said:

Gravity clearly is a force. Whether it is frame dependent or not is a different question.


That depends on the medium. In a non-polarized vacuum it is be the speed of light.


Any finite distance should give finite attenuation, just like all forces from finite sources.

In a dispersionless, sourceless, unpolarized medium the force attenuation law is r-2, where r is the distance from the source.


It seems to be one-to-one.


You mean this one? Then OK, please proceed.

You say Gravity is CLEARLY a force, any Force suggests an attendant particle carrying a specific type of Charge. Whilst the Graviton is theorised to carry such a charge for Gravity, none have ever been detected. I will be the first person to agree that possibly, we are employing the wrong type of Detector, and that the Science is not yet sufficiently advanced to detect this particle, but for the time being, it would be equally correct to claim that Gravity is an Effect of an as yet, unknown fundamental aspect of physics.

A non - polarized vacuum (Quantum Electrodynamic Theory) is an interesting idea, if such a postulate exists. WHY is it to be the Speed of Light (as determined by a vacuum that very well may not exist in nature)??

"Any finite distance should give finite attenuation": doesn´t really follow any Physical law (or postulate) attributed to Gravity. Please give a little more information.

I also would like to know why the Inverse Law can apply to to a "Force" that has no associated particle.

On an entirely different note Sepulchrave: IF Gravitons are finally detected then it follows that a means (a barrier) should also co-exist through which such particles cannot permeate? Does this make sense to you? It would be very interesting (from my point of view) to determine IF Gravity is a force, then there must be an equal and opposite force.


#33    Mikami

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Posted 25 February 2013 - 04:31 PM

Well I'd rather see 2 billion dollars spent on an Alpha Magnetic Spectrometer then being spent on oh I dunno.... Transformers 4?


#34    shrooma

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Posted 26 February 2013 - 02:29 PM

View PostWaspie_Dwarf, on 20 February 2013 - 09:30 PM, said:

it seems I don't understand when to use "their" and "there" either.
.
I hate people who don't know the difference between 'they're' and 'there'.
their SO stupid...!
:-D

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#35    shrooma

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Posted 26 February 2013 - 02:39 PM

i'm not sure that gravity is a 'force' as such, but rather a consequence of matter distorting the fabric of spacetime.
probably why 'gravitons' haven't been found, because there's no 'force' involved, and why it's resistant to unification, because it's an effect rather than a cause.....

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#36    sepulchrave

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Posted 26 February 2013 - 04:51 PM

View Postkeithisco, on 25 February 2013 - 04:02 PM, said:

You say Gravity is CLEARLY a force, any Force suggests an attendant particle carrying a specific type of Charge.
No it doesn't.
Perturbative quantum field theory suggests that any static force can be expressed as a superposition of virtual force carrying particles.

However it is well known that gravity cannot be meaningfully expressed in a quantum mechanical form using perturbation theory. Two immediate possibilities arise:
  • Gravity involves something ``extra'' (i.e. string theory), or
  • Gravity fundamentally cannot be treated with perturbation theory.
While #1 is the most popular opinion at the moment, there is nothing to explicitly rule out #2.

Secondly, gravity clearly causes a trajectory deviation in what we perceive as inertial motion.

If the GR approach is correct, gravity may be a ''fictitious force'' (like centrifugal force), but it still behaves like a force (in certain reference frames, at least).

View Postkeithisco, on 25 February 2013 - 04:02 PM, said:

A non - polarized vacuum (Quantum Electrodynamic Theory) is an interesting idea, if such a postulate exists. WHY is it to be the Speed of Light (as determined by a vacuum that very well may not exist in nature)??
IF the graviton is real, and gravity is a quantum field, then there will be graviton/anti-graviton ``bubbling'' in the quantum vacuum, and this could very well cause vacuum polarization analogous to the electromagnetic quantum field.

In this situation the quantum vacuum almost certainly is not a true vacuum, but that is due to constant self-interaction. The graviton, being massless, would still travel at speeds equal to or less than the ``ideal vacuum speed of light'', even if such a speed could never be realized in a true vacuum (the same is true for actual light in a quantum vacuum).

IF the graviton is not real, and gravity is a geometry effect, then the speed of gravitational waves is set by the properties of space-time, the consequences of Lorentz invariance requires this speed to be the speed of light.

In fairness, there is still debate about whether the speed of gravity has been experimentally proven to be equal to the speed of light.

View Postkeithisco, on 25 February 2013 - 04:02 PM, said:

"Any finite distance should give finite attenuation": doesn´t really follow any Physical law (or postulate) attributed to Gravity. Please give a little more information.

I also would like to know why the Inverse Law can apply to to a "Force" that has no associated particle.

Any force needs to come from a source. The quantity of force emanating from a closed region in space should depend only on the size of the source within that region.

For a spherical source in flat space, the total quantity of force at a distance r from the centre of that source is 4 pi r2 F®, where F® is the magnitude of the force parallel to r. Since the source is isotropic, and if the force is from monopoles, the force must also be isotropic, hence there is no portion of F® normal to r.
For the total quantity of the source to be the same (i.e. conserved) regardless of the distance from the source, we must have F® ~ r-2.

This is Gauss's law.

For weird-shaped objects, or curved space, the force law would be different (and no longer isotropic) but still derivable from the arguments above.

This is the same as the situation with electric charge; it is understood that the r-2 attenuation law is the ideal case for a test charge in a flat, dispersionless medium.

The existence of associated force-carrying particles actually makes the argument more complicated, as is mentioned in the article on vacuum polarization above. In this case the r-2 attenuation law is a truly ideal case where the quantum vacuum doesn't interfere. (In essence, the quantum vacuum can contain temporary sources for the force which can obviously interfere with the dispersion law, because some of these sources will be closer to the true source than our test position at r.)

View Postkeithisco, on 25 February 2013 - 04:02 PM, said:

On an entirely different note Sepulchrave: IF Gravitons are finally detected then it follows that a means (a barrier) should also co-exist through which such particles cannot permeate? Does this make sense to you? It would be very interesting (from my point of view) to determine IF Gravity is a force, then there must be an equal and opposite force.
I am not sure what you are saying.

There is no barrier for photons... photons couple to charge so IF there are charged particles in the photon's path THEN the photon can be absorbed (but might scatter or just fly through, it is a probabilistic argument), so I would assume the same is true for gravitons (absorbed, scattered, or transmitted through mass).

I do agree it makes sense to have an opposite force, but presumably that would come from a ``negative mass'' object.

Have you read up on the arguments for the gravitational behaviour of antimatter?


#37    third_eye

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Posted 26 February 2013 - 06:50 PM

I wish someone would write a new app called "speed googler"

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#38    Pyridium

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Posted 26 February 2013 - 11:43 PM

I will simply say that I believe that dark matter is mass that can not hold an electron.  I am speaking of individual quarks and clusters of quarks that are unstable and can not hold an electron.  8% of all matter became very stable atoms of hydrogen.  92% of the matter never formed into atoms, and never will.  It takes 3 quarks to form a proton.  Quarks come in all sizes and it takes some luck for a proton to be produced, like 8% worth.  The big bang spewed out all matter in the form of quarks, there was very little time for the formation of atoms.  Unstable quark clusters could not hold the electron, 92%.  That is my idea of dark matter.


#39    ancient astronaut

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Posted 05 March 2013 - 01:17 AM

It will be interesting if this in fact true.





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