Jump to content


Photo
- - - - -

What Is Dark Energy And Dark Matter?

Astronomy Dark Energy Particle Physics

  • Please log in to reply
21 replies to this topic

#1 Flummoxed

Flummoxed

    Explaining

  • Members
  • PipPipPipPipPipPip
  • 878 posts

Posted 31 January 2019 - 06:16 AM

Good Bye


Edited by Flummoxed, 07 March 2019 - 11:08 AM.


#2 exchemist

exchemist

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2841 posts

Posted 31 January 2019 - 06:27 AM

Just for those that like Nuggets with 3/4 of an hour to spare Erik Verlinde, Sabine Hossenfelder, Catherine Heymans debate dark matter

Erik Verlinde proponent of modified gravity, and no dark matter.

Sabine Hossenfelder also modified gravity plus a tiny bit of dark matter.

Catherine Heymans somethings bending light open minded maybe there is dark matter and maybe there isn't, wants a bigger mirror..

 

 

My view is biased since dark matter has never been detected it does not exist, like parallel universes. However Verlindes and Hossenfelders ideas require an :) understanding of what space is. Something a lot of people are in denial about :)

 

I'm puzzled by what you say. There is no observational evidence for dark energy, but there is for dark matter- we observe its gravitational effects. 


Edited by exchemist, 31 January 2019 - 06:28 AM.


#3 exchemist

exchemist

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2841 posts

Posted 31 January 2019 - 08:30 AM

The professional physicists said it not me, I merely presented it. :)

 

Dark energy drives the accelerating expansion of the universe. We observe light being bent by gravitational effects. All attempts at detecting what dark matter might be have failed. Neither Verlindes theories or Hossenfelders work support the existence of huge amounts of dark matter. Verlinde goes as far as to claim it does not exist, Hossenfelder mixes some of Verlindes ideas with her own, here is a link

 

"A generally covariant version of Erik Verlinde's emergent gravity model is proposed. The Lagrangian constructed here allows an improved interpretation of the underlying mechanism. It suggests that de-Sitter space is filled with a vector-field that couples to baryonic matter and, by dragging on it, creates an effect similar to dark matter. We solve the covariant equation of motion in the background of a Schwarzschild space-time and obtain correction terms to the non-covariant expression. Furthermore, we demonstrate that the vector field can also mimic dark energy. "https://arxiv.org/abs/1703.01415

Yes I see. But that's a bit different. We have evidence for dark matter through gravitational effects. What these people suggest is that maybe the effects we see, though consistent with matter that does not emit radiation, are actually due to something else.

 

This looks like MOND and all that: F proportional to 1/r,  at F < 10⁻¹¹g  etc.    



#4 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 31 January 2019 - 09:01 AM

 

 

 

My view is biased since dark matter has never been detected it does not exist, like parallel universes.

 

 

I'm with you.  Dark matter is the modern day equivalent of the "epicycle" in the geocentric ptolemic theory of yesteryear.  When the observations seem to refute your theory, what now?

 

Of course the answer can't be to reject your theory.  That's unthinkable, because the theory has always worked so well, and made so many accurate predictions.  You simply can't reject it's basic (geocentric) premises.  So what do you do?

 

You invent, ad hoc, the existence of some hitherto unknown phenomena, which themselves virtually destroy your initial premises (e.g., all motion in the quintessence is "perfect"--that is to say absolutely circular motion).  The nature of the quintessence, which harbors the perfect heavenly bodies, cannot be questioned.  Well, until it was necessary to invent epicycles, anyway.  We can give up, to some degree, our former notions of the quintessence but don't you EVER suggest that the earth is moving!

 

I mean, like, if you try to start going down that road, we'll burn your sorry *** at the stake, understand?


Edited by Moronium, 31 January 2019 - 09:22 AM.


#5 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 31 January 2019 - 09:04 AM

 We have evidence for dark matter through gravitational effects. 

 

 

What "gravitational effects?"  Like the ptolemicists, this simply seems to conclusively presuppose the indubitability of existing theory.

 

The whole problem with existing theory is that it completely breaks down.

 

Enter "dark matter" to "explain" this dismal failure.


Edited by Moronium, 31 January 2019 - 09:05 AM.


#6 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 31 January 2019 - 09:31 AM

The perfectly logical hypothesis that the solar system is heliocentric is an ancient one, going way back to Aristarchus around 300 B.C. But such a "blasphemous" proposition was prima facie unacceptable, ya know?   After all, the great one, Aristotle,  (and hence the Roman Catholic church) had given his imprimatur to geocentricism.

 

Geocentricism was sacrosanct, kinda like most "modern" theories are today.  Don't question them, if you know what's good for you.

 

Aint that right, Chem?


Edited by Moronium, 31 January 2019 - 09:38 AM.


#7 exchemist

exchemist

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2841 posts

Posted 31 January 2019 - 11:48 AM

You would be right Verlindes emergent gravity theory gives a theoretical basis to MOND. All the presenters agree that there is based on EFE evidence for dark matter, via gravitational lensing, however they all point out that EFE might like Newtons equations not be 100% correct, and gravity might work slightly differently. If EFE predict the existence of something that cant be proven to exist, then it might be a little wrong. Hosenfelder is mostly in agreeance with Verlinde that there is likely another explanation for Dark matter. 

Well it's interesting, I grant you. From what I read, there is not yet any definitive test for discriminating between the two ideas. Perhaps the astronomer prefer dark matter, as that neatly accounts for the gravity observations (rotation rates of galaxies, lensing etc),  while shovelling the problem onto the plates of the particle physicists, whereas some of the particle physicists try to pass it onto the speculative cosmologists to get rid of the issue that way! 

This is rather a nice example of the way contending models develop in science, to account for new phenomena. 

 

What I confess I do not quite follow is how both Newtonian and MOND gravitational models can be equally reconciled with General Relativity. If the field varies linearly with distance at very long range, surely the curvature of space in the GR representation will look different, won't it? (I confess that, as I chemist, I never learnt tensors, so I can't follow GR properly myself - I have to take it on trust from those that can.)



#8 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 31 January 2019 - 04:49 PM

Einstein took it upon himself to invent, ad hoc, a "cosmological constant" (which is basically an anti-gravity force) to explain how a supposedly "steady state" universe could remain steady and not collapse in on itself.

 

After Hubble's findings were published, Einstein repealed his constant, and declared that it was the biggest mistake he ever made.

 

Now it's back, with a new name:  "dark energy."  I guess fads kinda come and go (and then come back again) in scientific theory, eh?

 

Whatever it takes to try to "save the theory," ya know?


Edited by Moronium, 01 February 2019 - 11:02 AM.


#9 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 01 February 2019 - 10:51 AM

The math of MOND isnt too bad https://en.wikipedia...tonian_dynamics at the WIKI level, a lot more has been published on arxiv by the original author Milgrom. Verlindes theory and maths is I admit headache inducing, and I am not sure I follow all of it. Hossenfelders math is somewhere in the middle I think, and almost understandable.  

 

My money is on MOND.

 

"Spacetime," is just not a physically meaningful concept,  And it has been stretched to the most absurd extremes.  For example, in order to "patch up" SR when we observe superliminal speeds, they say the material objects in question are not moving at all.  The "space" between them is just expanding, they "explain."  I guess all motion is just an illusion, as Parmenides told us millennia ago, eh?


Edited by Moronium, 01 February 2019 - 10:56 AM.


#10 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 01 February 2019 - 11:09 AM

Nothing is sacrosanct except peoples religious beliefs. 

 

 

Well, it's seems that a lot of people have turned modern physical theory into a quasi-religious pursuit with all the zealous fervor of a dogmatic, bible-thumping fundy, know what I'm sayin?  It's quite mystical, replete with multi-universes, strings, 11 dimensions, etc.  All accepted (by some) on the basis of unwavering faith in "science."

 

The scenario of many unobserved universes plays the same logical role as the scenario of an intelligent designer. Each provides an untestable hypothesis that, if true, makes something improbable seem quite probable.

 

 

Lee Smolin, "The Trouble With Physics"


Edited by Moronium, 01 February 2019 - 11:20 AM.

  • Flummoxed likes this

#11 exchemist

exchemist

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2841 posts

Posted 01 February 2019 - 12:11 PM

The math of MOND isnt too bad https://en.wikipedia...tonian_dynamics at the WIKI level, a lot more has been published on arxiv by the original author Milgrom. Verlindes theory and maths is I admit headache inducing, and I am not sure I follow all of it. Hossenfelders math is somewhere in the middle I think, and almost understandable.  

Thanks, yes I see how Milgrom makes it work from a Newtonian perspective. I'd need a comment from a GR specialist to understand how it is handled in the GR maths. There was a chap called Markus Hanke on another forum who was very good at this sort of thing. Though you needed all neurons firing to follow, at times. :)


Edited by exchemist, 01 February 2019 - 12:11 PM.

  • Flummoxed likes this

#12 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 01 February 2019 - 12:38 PM

The beauty of dark matter as a solution is that it can never be observed, just deduced from other premises.  This makes any claim that it exists unassailable by empirical means.

 

Of course, on the downside, it's just reduced to non-falsifiable pseudo-science, in Popper's terms.  There seems to be many cases where theoretical propositions which at one time would have been rejected as pseudo-science are now "mainstream science."  It doesn't take much, if any, evidence to convince members of the choir.

 

The majority of astronomers, astrophysicists and cosmologists accept...and are committed to a dark matter solution of the missing-mass problem.

 

 

https://en.wikipedia...tonian_dynamics

 

I wonder how long it will be before major universities will be offering degrees in astrology.  I'm sure it would be a very popular major.  It's obviously scientific because it has math formulas.  There would be money in it and no shortage of sheep to fleece.


Edited by Moronium, 01 February 2019 - 01:05 PM.


#13 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 02 February 2019 - 08:37 AM

My money is on MOND.

 

"Spacetime," is just not a physically meaningful concept, 

 

 

I'm no expert on GR, by any means, but I understand that the fundamental sourrce of the conflict between QM and GR is that QM, contrary to GR, presupposes a flat, Euclidean, space consisting of 3 + 1 dimensions (i.e., where time is not mysteriously deemed to be a hypothetical fourth dimension, inseparable from the other three).

 

For this reason, John S. Bell (of Bell's theorem notoriety), among others, has suggested that the simplest way to resolve the conflict is to revert to a Lorentzian conception of relative motion, which presumes absolute simultaneity and eschews SR's concept of "relative simultaneity."

 

... I would say that the cheapest resolution is something like going back to relativity as it was before Einstein, when people like Lorentz and Poincare thought that there was an aether—a preferred frame of reference—but that our measuring instruments were distorted by motion in such a way that we could not detect motion through the aether. Now, in that way you can imagine that there is a preferred frame of reference, and in this preferred frame of reference things do go faster than light. ... Behind the apparent Lorentz invariance of the phenomena, there is a deeper level which is not Lorentz invariant... [This] pre-Einstein position of Lorentz and Poincare, Larmor and Fitzgerald (sic), was perfectly coherent, and is not inconsistent with relativity theory. (J. S. Bell)

 

 

https://pdfs.semanti...40f9c00d541.pdf

 

As far as I know, there is no known phenomena which are purportedly "explained" by "spacetime" which cannot be adequately explained without invoking the notion of "spacetime."  The concept of spacetime is a postulated notion that can never be empirically verified.


Edited by Moronium, 02 February 2019 - 10:14 AM.


#14 Flummoxed

Flummoxed

    Explaining

  • Members
  • PipPipPipPipPipPip
  • 878 posts

Posted 03 February 2019 - 04:51 AM

I'm no expert on GR, by any means, but I understand that the fundamental sourrce of the conflict between QM and GR is that QM, contrary to GR, presupposes a flat, Euclidean, space consisting of 3 + 1 dimensions (i.e., where time is not mysteriously deemed to be a hypothetical fourth dimension, inseparable from the other three).

 

For this reason, John S. Bell (of Bell's theorem notoriety), among others, has suggested that the simplest way to resolve the conflict is to revert to a Lorentzian conception of relative motion, which presumes absolute simultaneity and eschews SR's concept of "relative simultaneity."

 

 

https://pdfs.semanti...40f9c00d541.pdf

 

As far as I know, there is no known phenomena which are purportedly "explained" by "spacetime" which cannot be adequately explained without invoking the notion of "spacetime."  The concept of spacetime is a postulated notion that can never be empirically verified.

 

Special Relativity gives the same answers as Lorentz Ether Theory. From this point of view they are equivalent. General Relativity reduces to SR when no gravitational masses are present, ie no "apparent" space time curvature. LET failed to predict the perihelion advance of Mercury accurately, unlike GR which calculated it correctly. Also GR does not require a undetectable ether. :)

The existence of the ether is inferred and undetectable except by observed effects  :goodbad: , not unlike dark matter  :innocent: . Is dark matter just an observed effect of how space works, and not an actual substance. 

 

All of the theoretical physicists above agree there is an observed effect of dark matter and all of them are prepared to accept that perhaps GR is perhaps wrong, all of them have tested or put forward other explanations, which dont require huge random amounts of dark matter. They are also putting their credibility on the line.

 

Many physicists and those interested etc on science forums argue that dark matter absolutely must exist, and anyone suggesting otherwise is wrong or some kind of wack case. The existence of Dark Matter must be discussed as if it is a fact, like some religious belief.  



#15 Flummoxed

Flummoxed

    Explaining

  • Members
  • PipPipPipPipPipPip
  • 878 posts

Posted 03 February 2019 - 04:56 AM

Thanks, yes I see how Milgrom makes it work from a Newtonian perspective. I'd need a comment from a GR specialist to understand how it is handled in the GR maths. There was a chap called Markus Hanke on another forum who was very good at this sort of thing. Though you needed all neurons firing to follow, at times. :)

 

He has his own website https://www.markushanke.net/ is this the right guy ?



#16 Moronium

Moronium

    Creating

  • Members
  • PipPipPipPipPipPipPip
  • 2894 posts

Posted 03 February 2019 - 05:07 AM

Special Relativity gives the same answers as Lorentz Ether Theory. From this point of view they are equivalent. General Relativity reduces to SR when no gravitational masses are present, ie no "apparent" space time curvature. LET failed to predict the perihelion advance of Mercury accurately, unlike GR which calculated it correctly. Also GR does not require a undetectable ether. :)

The existence of the ether is inferred and undetectable except by observed effects  :goodbad: , not unlike dark matter  :innocent: . Is dark matter just an observed effect of how space works, and not an actual substance. 

 

All of the theoretical physicists above agree there is an observed effect of dark matter and all of them are prepared to accept that perhaps GR is perhaps wrong, all of them have tested or put forward other explanations, which dont require huge random amounts of dark matter. They are also putting their credibility on the line.

 

Many physicists and those interested etc on science forums argue that dark matter absolutely must exist, and anyone suggesting otherwise is wrong or some kind of wack case. The existence of Dark Matter must be discussed as if it is a fact, like some religious belief.  

 

In many cases, yes, you get the same predictions, but not all (such as in the GPS and the H-K experiment) as I have discussed in other threads.  The ether is by no means essential to a preferred frame theory, although it's true that Lorentz posited one.  There are other ways of establishing a preferred frame.

 

Neither SR or LR has anything to say about Mercury.  They are both theories of relative motion, not theories of gravity, like GR.  Einstein said that GR was "unthinkable" without positing an ether.

 

As I said before, dark matter is reminiscent of ad hoc epicycles, and likely just as fictitious.  The postulation of dark matter presupposes the indubitability  of GR, but it is GR that has broken down.  As I said, my money in on MOND.


Edited by Moronium, 03 February 2019 - 05:09 AM.


#17 Flummoxed

Flummoxed

    Explaining

  • Members
  • PipPipPipPipPipPip
  • 878 posts

Posted 03 February 2019 - 05:26 AM

He has his own website https://www.markushanke.net/ is this the right guy ?

 

HaHa He has a link to emergent gravity on his forum https://www.markusha...ergent-gravity/

 

and not too many firing neurons are required to follow what he says.


Edited by Flummoxed, 03 February 2019 - 05:35 AM.




Also tagged with one or more of these keywords: Astronomy Dark Energy, Particle Physics