Almost certainly not. Do epicycles exist? No. They were a handy tool/kludge. Our understanding of space-time is incomplete.
Could dark matter not exist?
81–90 of 102 posts
Re: Could dark matter not exist?
#82Earlier quoted context omitted.
There's nothing magical about the required properties, so I'm not sure why anyone would describe them that way. They are no different than the properties imputed to neutrinos or the aether: http://www.tjradcliffe.com/?p=1801 The important thing about extra-galactic dark matter is there is too much of it to be made of ordinary particles: protons and neutrons and electrons. We know how many ordinary nucleons there are…
I'll try to explain what I meant about magic. Your piece was interesting on how building mental models is an important part of science which opened my eyes a bit. However, in terms of this discussion I was thinking there might be lower-hanging fruit that makes dark matter appear farther-fetched. For example, we have calculated the mass of a galaxy, but it doesn't spin right at that mass. So, instead of: 1. Assuming o…
> 1. Assuming our calculations are wrong
That's what this is. We checked the math 20 times over and we know the model is wrong.
> 2. There is more interstellar dust/gas/solar-wind mass than we realize
We checked.
> 3. Heavier Black hole at center, or spinning speed/time dilation occurring?
Doesn't fit.
> 4. Effects of gravity are weaker at very long distances
Also an extraordinary claim, has not been ruled out.
Plus we already have confirmed 'undetectable' substances, so it's not very strange to suggest a new one.
Re: Could dark matter not exist?
#83Earlier quoted context omitted.
The name isn't great. It sounds like matter that doesn't produce light, when it's really "matter" that's invisible. But not matter you can touch. Which makes it not really matter in normal English. You probably can't see it either. So "Invisible Untouchable Gravitation Sources" would be a more descriptive name. I don't think it'll catch on.
Perhaps it could be some form of friction we don't yet understand? I mean a form of gravitational friction? The nice part of being an armchair physicist is spouting off nonsense - I suppose if I really wanted to find out, I could make up a mathematical model of my theory and then find out if the evidence fits. Sadly, I really have no idea how to do that!
A more interesting interpretation would be that the observable universe could be near a parallel unobservable universe and that gravity of that universe is influencing current universe.
Re: Could dark matter not exist?
#84Sigh. Sure, it's possible, but very unlikely. These "MOND" gravity theories purport to explain observations better than the theory of dark matter, but they don't. They explain some things and leave gaping holes elsewhere. On the whole they are hugely inferior theories in terms of matching observational evidence. Their only advantage is that they lack the existence of massive, weakly interacting particles, which a lot…
> These "MOND" gravity theories purport to explain observations better than the theory of dark matter, but they don't. MOND consistently fits the rotational velocity profile of galaxies better than dark matter. This isn't too surprising as MOND originated as an ad-hoc formula derived from observations of said rotational profiles, however MOND works very well over a very wide range of galactic profiles. The mass defic…
> A combination of MOND and dark matter matches most observations very well, far better than dark matter in isolation.
Isn't that unsurprising that a theory with more degrees of freedom can fit the data better? It's hard to say if this is interesting without knowing if it fits data significantly enough better to make up for the extra parameters. Dark matter (well, Lambda-CDM) is appealing for being able to fit a wide range of observations with a fairly simple model that's entirely compatible with GR.
Re: Could dark matter not exist?
#85Earlier quoted context omitted.
Actually you can unify E and B into a closed two-form F and get in vacuum dF = 0 d★F = ★j Where j = rho dt + jx dx + jy dy + jz dz is the charge and current density, ★ is the Hodgestar operator and d is the exterior derivative. The equations in a medium are slighly less elegant.
And if you write the electromagnetic field in terms of the 4-vector potential, it's just \Box{A_μ} = 0 (where Box is the D'Alembertian operator). Then again, this doesn't really mean anything without the context of what the notation means... Feynman has a discussion about this in Volume 2 of the Feynman Lectures: http://www.feynmanlectures.caltech.edu/II_25.html (I still can't get over how awesome it is that I can de…
That's a charge that applies equally well to the standard formulation and I made this comment just to say that it IS cool you can deeplink the Feynman lectures!
Re: Could dark matter not exist?
#86It reads like a great example of how theory works. You have some evidence (old planets), and a model that predicts it well (Newton/Kepler). Then some new evidence comes in (Uranus), and the theory is almost right, but not quite. So we modify it a little, or we start searching for an extra mass to explain the error. Then some more experimental evidence comes in (galactic radial velocity), and we are thinking about mod…
I recommend you to read the work of an astrophysicist Alexander F. Mayer (Stanford): http://www.sensibleuniverse.net/ who proves that the theory of the universe as we know since Einstein is wrong.
Re: Could dark matter not exist?
#87Earlier quoted context omitted.
In geometric algebra it's a single equation. ∇E=∂B/∂t
what is B?
http://www.maxwells-equations.com/ will answer all your questions... :-)
Re: Could dark matter not exist?
#88Earlier quoted context omitted.
Ditto. Out of curiosity, is dark matter spread unevenly throughout the universe, or is it directly inverse to matter? Like, when we expect dark matter causes an effect, is it because we expect there to be a massive dark-matter "object" acting upon matter, or can we attribute it to denser dark matter as space between matter increases? Edit: would viewing dark matter provide a negative image of the universe? I'm asking…
No, dark matter is definitely not the inverse of regular matter. Dark matter is spread unevenly through the universe, and it's spread in a pretty similar (but still notably different) way to the spread of regular matter. For example, where you have galaxies with lots of regular matter there is also lots of dark matter, but it has a slightly different distribution. You seem to be imagining something cool, but not some…
Thanks for that! I realize it was a pretty n00b question, I appreciate you taking the time. :)
Re: Could dark matter not exist?
#89Earlier quoted context omitted.
> Real science is rarely so clean. I'm no physicist but I've never liked dark matter and dark energy: they smell suspiciously similar to hacks (the bad kind) if a hack could be defined as over-fitting a solution to a problem. It seems as though, recently, science has become rather bad at the words "I don't know." Things were staying together more than they should so we invented dark matter in order to explain that. N…
Well, it would be pretty useless if we named every unproven theory simply "don't know". Perhaps we should call it "dark matter hypothesis", but that also gets awkward after a while.
I think physicists know its an hypothesis, the problem is when its presented to the general public as an universal indisputable truth of science.
You know, those documentaries with the narrator assuming you're a two years old, spoiling the conclusion at the beginning and repeating it as a teaser every 5 minutes? Or all of those "I Love Science" pages. People should stop trying to make science a reality show.
Re: Could dark matter not exist?
#90It reads like a great example of how theory works. You have some evidence (old planets), and a model that predicts it well (Newton/Kepler). Then some new evidence comes in (Uranus), and the theory is almost right, but not quite. So we modify it a little, or we start searching for an extra mass to explain the error. Then some more experimental evidence comes in (galactic radial velocity), and we are thinking about mod…
> Real science is rarely so clean. I'm no physicist but I've never liked dark matter and dark energy: they smell suspiciously similar to hacks (the bad kind) if a hack could be defined as over-fitting a solution to a problem. It seems as though, recently, science has become rather bad at the words "I don't know." Things were staying together more than they should so we invented dark matter in order to explain that. N…
> they smell suspiciously similar to hacks (the bad kind) if a hack could be defined as over-fitting a solution to a problem.
Dark matter is not over-fitting - as described in article, it does not explain galaxy radial velocity as well as MOND. In addition to that, dark matter explains much more and successfully predicted few things. While MOND only described galaxy radial velocity better, but completely failed all the other things. So MOND seems to be the overfitting one.
Physics have theories that are best so far, nobody claims they are 100% proven.