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Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

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Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#31

Post by PartiallyTyped »

andrewflnr wrote: post #29
PartiallyTyped wrote: post #28

Earlier quoted context omitted.

Could you elaborate? It’s a set of observations about “something” that behaves like matter[1], and interacts only gravitationally. There are many theories proposed but none has any real answers or solutions. The following is taken from Cern[2]: > Many theories say the dark matter particles would be light enough to be produced at the LHC. If they were created at the LHC, they would escape through the detectors unnotic…

The way she wants to use "dark matter", MOND is a dark matter theory (explains (some of) the same observations), and no one else uses it that way. "Dark matter" always means some kind of matter, whatever the specifics. Think of it as a family of theories if that helps.

I don’t see where we (or she for that matter —hah!) disagree.

She agrees that Dark Matter is observations or a problem for something that seems to be matter from our definitions of matter and its interactions.

She didn’t claim that MOND is the only theory or answer — in fact she made a video about this exactly, that she believes she failed to adequately argue that DM is what we are discussing because people put too much emphasis on MOND or thought of it as “the only solution to the DM problem”.

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#32

Post by krapp »

MaxikCZ wrote: post #27
NoMoreNicksLeft wrote: post #12

If there is distinct "negative mass" out there, does that mean that we can built FTL devices after all? Or do we also need negative energy?

There's no evidence, physical or theoretical, of negative mass. (Yet.) But yes. If there's a negative mass we learn to control, possibility of FTL drive goes from "Absolutely not" to "Umm, maybe?".

The caveat being the Fermi Paradox. If FTL were possible, someone else should have figured it out by now and colonized the galaxy, and so we should see evidence of warp drives and galaxy-scale civilization everywhere. Since we don't see evidence of anything of the sort, FTL in any form probably isn't possible. Negative mass either doesn't exist or isn't useful.

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#33

Post by andrewflnr »

PartiallyTyped wrote: post #31
andrewflnr wrote: post #29

Earlier quoted context omitted.

The way she wants to use "dark matter", MOND is a dark matter theory (explains (some of) the same observations), and no one else uses it that way. "Dark matter" always means some kind of matter, whatever the specifics. Think of it as a family of theories if that helps.

I don’t see where we (or she for that matter —hah!) disagree. She agrees that Dark Matter is observations or a problem for something that seems to be matter from our definitions of matter and its interactions. She didn’t claim that MOND is the only theory or answer — in fact she made a video about this exactly, that she believes she failed to adequately argue that DM is what we are discussing because people put too m…

Are you actually reading what I'm saying? Can you tell the difference between a claim about whether a theory is true and how it is best categorized?

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#34

Post by rthnbgrredf »

I think the simplest explanation for dark matter is that it consists of something we already know exists and behaves exactly like dark matter: black holes. To fit this explanation, we would need a vast number of black holes, each relatively small, approximately the size of a tennis ball. These black holes would be large enough to have persisted since the early universe, avoiding conversion into Hawking radiation. The remaining question is how such a multitude of primordial black holes could have formed in the early universe. The most likley answer to this question is density fluctuations. During the very early moments after the Big Bang, slight variations in density could have caused regions of space to collapse under their own gravity, forming black holes. If the density contrast was large enough, these regions would collapse directly into black holes.

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#35

Post by PartiallyNerdy »

andrewflnr wrote: post #33
PartiallyTyped wrote: post #31

Earlier quoted context omitted.

I don’t see where we (or she for that matter —hah!) disagree. She agrees that Dark Matter is observations or a problem for something that seems to be matter from our definitions of matter and its interactions. She didn’t claim that MOND is the only theory or answer — in fact she made a video about this exactly, that she believes she failed to adequately argue that DM is what we are discussing because people put too m…

Are you actually reading what I'm saying? Can you tell the difference between a claim about whether a theory is true and how it is best categorized?

I claimed dark matter is something we observed and dark matter “theories” are proposed but yet to be proven theories that describe it.

She did that too.

She didn’t claim Mond is true, neither did I, and as far as I can understand you, neither did you.

If you assume me or her did that, then you’ve grossly misunderstood mine or her remarks.

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#36

Post by matthewdgreen »

rthnbgrredf wrote: post #34

I think the simplest explanation for dark matter is that it consists of something we already know exists and behaves exactly like dark matter: black holes. To fit this explanation, we would need a vast number of black holes, each relatively small, approximately the size of a tennis ball. These black holes would be large enough to have persisted since the early universe, avoiding conversion into Hawking radiation. The…

Wouldn’t these black holes radiate some Hawking radiation, making them potentially detectable? And how long would they exist for? Also what keeps these black holes from interacting with normal matter and clumping in the center of galaxies?

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#37

Post by rthnbgrredf »

matthewdgreen wrote: post #36
rthnbgrredf wrote: post #34

I think the simplest explanation for dark matter is that it consists of something we already know exists and behaves exactly like dark matter: black holes. To fit this explanation, we would need a vast number of black holes, each relatively small, approximately the size of a tennis ball. These black holes would be large enough to have persisted since the early universe, avoiding conversion into Hawking radiation. The…

Wouldn’t these black holes radiate some Hawking radiation, making them potentially detectable? And how long would they exist for? Also what keeps these black holes from interacting with normal matter and clumping in the center of galaxies?

You ask very good questions.

> Wouldn’t these black holes radiate some Hawking radiation, making them potentially detectable?

Yes, according to widely accepted theory, they do. However, Hawking radiation is incredibly weak. With current technology, we are not able to detect such a faint signal.

> And how long would they exist for?

This depends on the size of the black hole. They will last much longer than our solar system, many billions of years, until they eventually evaporate.

> Also, what keeps these black holes from interacting with normal matter and clumping in the center of galaxies?

They do interact with normal matter via gravitation. If primordial black holes exist, many of them would fall into the supermassive black hole at the center of our galaxy and other galaxies. However, there are also those that orbit around the center. The problem is that our telescopes currently cannot detect a tennis ball-sized black object with the mass of a few Earths, it is an incredible tiny black dot in front of a black background. Hence, they are literally dark matter.

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#38

Post by PartiallyTyped »

PartiallyTyped wrote: post #21
suzzer99 wrote: post #15

Here's something I've wondered. If the universe is made up of 85% dark matter, does that mean we can assume black holes are also made up of the same ratio of dark matter to regular matter (or at least when it went into the black hole)?

IANAP (physicist) The only the matter portion of the universe is 85% dark matter (26.8% of mass-energy content of the universe). As for the question; I don't think it's right to assume that dark matter really is exotic matter. It's just a set of observations. It's something that behaves like matter (with respect to density scaling) but only seems to interact gravitationally. Some theories posit that it's some unknown…

Please tell me what I said that’s wrong instead of outright downvoting.

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#39

Post by andrewflnr »

PartiallyNerdy wrote: post #35
andrewflnr wrote: post #33

Earlier quoted context omitted.

Are you actually reading what I'm saying? Can you tell the difference between a claim about whether a theory is true and how it is best categorized?

I claimed dark matter is something we observed and dark matter “theories” are proposed but yet to be proven theories that describe it. She did that too. She didn’t claim Mond is true, neither did I, and as far as I can understand you, neither did you. If you assume me or her did that, then you’ve grossly misunderstood mine or her remarks.

> She didn’t claim Mond is true, neither did I, and as far as I can understand you, neither did you.

Well I'm glad we're clear on that. But then why did you feel the need to say

> She didn’t claim that MOND is the only theory or answer

As if that was a question anyone was asking?

Re: Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

#40

Post by irjustin »

rthnbgrredf wrote: post #34

I think the simplest explanation for dark matter is that it consists of something we already know exists and behaves exactly like dark matter: black holes. To fit this explanation, we would need a vast number of black holes, each relatively small, approximately the size of a tennis ball. These black holes would be large enough to have persisted since the early universe, avoiding conversion into Hawking radiation. The…

This was covered by PBS spacetime:

https://www.youtube.com/watch?v=qy8MdewY_TY&t=67s

Still possible, but increasingly unlikely due to the narrowing size range in which these black holes are allowed to exist in.

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