Dark Matter Question
Discussion
deckster said:
There are other candidate hypotheses to explain it though, mainly involving weird things happening to gravity.
And the beautiful think about physics is they probably call it a weird particle 
I find this stuff fascinating, but I listened to a Life Scientific with Edward Witten talking about M-theory the other day....and still have no idea what it is
SpudLink said:
Earlier in the thread someone mentioned MOND as one of the alternate theories of gravity that could explain away dark matter.
This YouTube video on the subject just popped up…
I am not a fan of MOND. It just seems a real fudge. The proponents don’t seem to give a reason why the strength of gravity should change. It just seems a way of making the formulas fit the observations. At least that is my understanding of it. This YouTube video on the subject just popped up…
I recently watched a video that suggests that the currently generally accepted hypothesis about the universe being an expanding bubble was more than likely wrong and that data from the Max Planck mission fits the model of a surface much more acurately.
found it - about 2/3 to 3/4 in through....
https://www.youtube.com/watch?v=lFlu60qs7_4
The more you know, the more questions you have.
found it - about 2/3 to 3/4 in through....
https://www.youtube.com/watch?v=lFlu60qs7_4
The more you know, the more questions you have.
Edited by coanda on Sunday 12th November 14:23
Edited by coanda on Sunday 12th November 14:24
deckster said:
RizzoTheRat said:
Fair point in theory vs hypothesis, but the guy who came up with Dark Energy got a Nobel prize for it so I thought it was fairly well accepted?
He was on Infinite Monkey Cage some time back and reckoned he'd got the prize for reducing the total amount of human knowledge by finding such a massive unknown
To be more accurate, the three who were jointly awarded the Nobel got it for the discovery that the universe was expanding faster than can be explained by the amount of matter (== energy) that we see in the universe. Dark energy is the name we give to the hypothesis that there is some invisible, unknown energy that is driving this expansion. There are other candidate hypotheses to explain it though, mainly involving weird things happening to gravity.He was on Infinite Monkey Cage some time back and reckoned he'd got the prize for reducing the total amount of human knowledge by finding such a massive unknown
But either way this is a great example: our observation is that the universe is expanding faster than our current theories allow. Therefore something is wrong. We hypothesise a number of solutions that would explain what we observe. We test to see if any of the hypotheses are correct. This is literally how science works
Which is driving certain parts of the anti big bang group wild.
Not saying either is correct, but it certainly is fascinating.
annodomini2 said:
deckster said:
RizzoTheRat said:
Fair point in theory vs hypothesis, but the guy who came up with Dark Energy got a Nobel prize for it so I thought it was fairly well accepted?
He was on Infinite Monkey Cage some time back and reckoned he'd got the prize for reducing the total amount of human knowledge by finding such a massive unknown
To be more accurate, the three who were jointly awarded the Nobel got it for the discovery that the universe was expanding faster than can be explained by the amount of matter (== energy) that we see in the universe. Dark energy is the name we give to the hypothesis that there is some invisible, unknown energy that is driving this expansion. There are other candidate hypotheses to explain it though, mainly involving weird things happening to gravity.He was on Infinite Monkey Cage some time back and reckoned he'd got the prize for reducing the total amount of human knowledge by finding such a massive unknown
But either way this is a great example: our observation is that the universe is expanding faster than our current theories allow. Therefore something is wrong. We hypothesise a number of solutions that would explain what we observe. We test to see if any of the hypotheses are correct. This is literally how science works
Which is driving certain parts of the anti big bang group wild.
Not saying either is correct, but it certainly is fascinating.
https://www.universetoday.com/161419/astronomers-h...
Toltec said:
Being careful about your point about accepted there are three or four ways, one of which is also producing good results.
https://www.universetoday.com/161419/astronomers-h...
A fascinating article. Thank you for posting.https://www.universetoday.com/161419/astronomers-h...
Having just come across this paper from 2002 ( better late than never ) I have ordered his book, article proposes an explanation of Cosmic Inflation ( not a theory ) encompassing Dark energy / Dark matter, theory may well have moved by now to levels beyond my comprehension / ability, article written at the level of " A Brief history in Time "
https://physics.mit.edu/wp-content/uploads/2021/01...
https://physics.mit.edu/wp-content/uploads/2021/01...
Panamax said:
Yes indeed. It would be better if "dark matter" was simply called "invisible matter", because there's nothing dark about it.
Similarly "dark energy" might more usefully be called "unknown energy".
But that wouldn't be sexy and mysterious.Similarly "dark energy" might more usefully be called "unknown energy".
It would be like calling Black Magic a box of chocolates.
Eric Mc said:
Dark matter is deduced through its gravitational effects. So it does interact with other matter in the universe. in fact, it's the interation that suggests it exists in the first place.
Suggest everyone reads Pharis Williams' The Dynamic Theory in which he derives - from first principles - equations of physics which don't require Dark Matter or Dark Energy in order to make sense.Dark Matter
Because the gravitational field strength diminishes in time this means that an object at distance away from the gravitating body would be responding to a gravitational field that was stronger when it left the gravitating body. Therefore, the stars in the arms of the spiral galaxies are responding to a gravitational field strength that was greater in the past when its effects would have left the galaxy center.
Visualisation of observed outer portions of spiral galaxies moving faster than expected led to the dark matter hypothesis. Simply imagine a weakening gravitational effect over time accounts for this. In The Dynamic Theory the time-dependent gravitational field shows that the tangential velocity of the stars is the result of a time-dependent gravitational field, and dark matter is not necessary.
The first order approximation to this time dependent effect is the same as the Modified Newtonian Dynamics (MOND) that has been hypothesized for the explanation of this effect.
Dark Energy
The time-dependence of gravity also results in a time-dependence of the Chandrasekhar limiting mass used to calculate the luminosity of type Ia supernovas. The result is that they are not constant in time as predicted by the standard model.
This is important, because they are used as the "standard candle" when determining the expansion of the universe. If the standard candle calculation is incorrect (and includes time-dependant terms), the need for Dark Energy to explain away the discrepancies drops away.
Well worth a read. Time-dependence of gravity is not a new idea, going back to Dirac in the 1930s. Williams simply sets it in an internally-consistent mathematical context.
skwdenyer said:
Eric Mc said:
Dark matter is deduced through its gravitational effects. So it does interact with other matter in the universe. in fact, it's the interation that suggests it exists in the first place.
Suggest everyone reads Pharis Williams' The Dynamic Theory in which he derives - from first principles - equations of physics which don't require Dark Matter or Dark Energy in order to make sense.Dark Matter
Because the gravitational field strength diminishes in time this means that an object at distance away from the gravitating body would be responding to a gravitational field that was stronger when it left the gravitating body. Therefore, the stars in the arms of the spiral galaxies are responding to a gravitational field strength that was greater in the past when its effects would have left the galaxy center.
Visualisation of observed outer portions of spiral galaxies moving faster than expected led to the dark matter hypothesis. Simply imagine a weakening gravitational effect over time accounts for this. In The Dynamic Theory the time-dependent gravitational field shows that the tangential velocity of the stars is the result of a time-dependent gravitational field, and dark matter is not necessary.
The first order approximation to this time dependent effect is the same as the Modified Newtonian Dynamics (MOND) that has been hypothesized for the explanation of this effect.
Dark Energy
The time-dependence of gravity also results in a time-dependence of the Chandrasekhar limiting mass used to calculate the luminosity of type Ia supernovas. The result is that they are not constant in time as predicted by the standard model.
This is important, because they are used as the "standard candle" when determining the expansion of the universe. If the standard candle calculation is incorrect (and includes time-dependant terms), the need for Dark Energy to explain away the discrepancies drops away.
Well worth a read. Time-dependence of gravity is not a new idea, going back to Dirac in the 1930s. Williams simply sets it in an internally-consistent mathematical context.
They propagate outwards but diminish in strength as they radiate outwards?
dukeboy749r said:
skwdenyer said:
Well worth a read. Time-dependence of gravity is not a new idea, going back to Dirac in the 1930s. Williams simply sets it in an internally-consistent mathematical context.
So, akin to the ripples in a body of water (for example)?They propagate outwards but diminish in strength as they radiate outwards?
Time-dependence of gravity is the theory that the fundamental strength of gravity (broadly speaking, the value of the gravitational constant G) has varied throughout the history of the universe. Although it's indeed not a new proposition there is no observational evidence for it, and by no means is it accepted physics. But it is an intriguing possibility for sure and without doubt it would explain some of the things we are now observing; that said, it introduces other complexities and inconsistencies in itself which is one reason why it hasn't seen broader acceptance.
deckster said:
dukeboy749r said:
skwdenyer said:
Well worth a read. Time-dependence of gravity is not a new idea, going back to Dirac in the 1930s. Williams simply sets it in an internally-consistent mathematical context.
So, akin to the ripples in a body of water (for example)?They propagate outwards but diminish in strength as they radiate outwards?
Time-dependence of gravity is the theory that the fundamental strength of gravity (broadly speaking, the value of the gravitational constant G) has varied throughout the history of the universe. Although it's indeed not a new proposition there is no observational evidence for it, and by no means is it accepted physics. But it is an intriguing possibility for sure and without doubt it would explain some of the things we are now observing; that said, it introduces other complexities and inconsistencies in itself which is one reason why it hasn't seen broader acceptance.
Occam's Razor says gravity has time-dependence, not that there's a lot of additional stuff we can't see or detect... 
skwdenyer said:
Occam's Razor says gravity has time-dependence, not that there's a lot of additional stuff we can't see or detect...
Does this theory have any answer for the Bullet cluster problem?budgie smuggler said:
skwdenyer said:
Occam's Razor says gravity has time-dependence, not that there's a lot of additional stuff we can't see or detect...
Does this theory have any answer for the Bullet cluster problem?But worth noting there are other theories that can explain it without Dark Matter - the Hyperbolic Universe, for instance.
skwdenyer said:
Au contraire, there *is* observational evidence for it - the very existence of that observational evidence is what led to the construction of a theory of Dark Matter Occam's Razor says gravity has time-dependence, not that there's a lot of additional stuff we can't see or detect...
We're going to have to differ on the definition of the word "evidence" Occam's Razor says gravity has time-dependence, not that there's a lot of additional stuff we can't see or detect... Observations have indeed shown there is something funky going on. Time-dependent gravity is one potential proposed solution, as is the existence of dark matter. As are other theories, as you've noted. I wouldn't say that our observations right now are evidence either way of the correctness of any of these.
deckster said:
skwdenyer said:
Au contraire, there *is* observational evidence for it - the very existence of that observational evidence is what led to the construction of a theory of Dark Matter Occam's Razor says gravity has time-dependence, not that there's a lot of additional stuff we can't see or detect...
We're going to have to differ on the definition of the word "evidence" Occam's Razor says gravity has time-dependence, not that there's a lot of additional stuff we can't see or detect... Observations have indeed shown there is something funky going on. Time-dependent gravity is one potential proposed solution, as is the existence of dark matter. As are other theories, as you've noted. I wouldn't say that our observations right now are evidence either way of the correctness of any of these.
I tend to think it’s more likely our theory is wrong rather than we’ve simply failed to detect a very large percentage of the mass in the universe, mass that doesn’t interact with us (we can fly right through it), but does create a gravitational lensing effect. Conditional mass, as it were.
Dark Matter is, to me, an Elastoplast designed to keep physics orthodox alive, rather than a seriously plausible outcome.
Gassing Station | Science! | Top of Page | What's New | My Stuff