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Examining the Expected Effects of Dark Matter On the Solar System
First time accepted submitter LiavK writes "Ethan Siegel recently wrote a great post for ScienceBlogs discussing the expected total mass of dark matter in the solar system. As far as we can tell, dark matter only interacts weakly, via gravity, both with itself and normal matter. So, it can't collide with itself, meaning that it has no way of getting hotter and radiating away energy and momentum. This means that it remains a diffuse mess, with a density that is ridiculously low, to the point where detecting its local effects is likely to remain... challenging for the foreseeable future."
Dark matter, the Ether of the 21st century.
Michelson and Morley found that the hypothetical ether had no detectable effects.
In contrast, scientists started by measuring orbital velocities and could only explain them with dark matter.
The problem with dark matter observation in this case is that science is based on empirical observation. If you can't see it, can't measure it, and can't even draw inferences from what you can see and measure to detect something indirectly... it's not science. What this is saying is that the effects are so miniscule that there is no equipment presently capable of separating an actual effect or observation from systemic inaccuracy in the equipment itself. That is, you can't tell whether it's just random 'noise' or an actual signal.
As I understand it, there's a big empty space in most of our theories and observations that says something should be filling it up, but we have very little in the way of actual data of what exists within this hole. We can infer something is needed to balance out our observations, but we haven't actually seen the 'something'. It's like a shy cat in an apartment. You won't see that cat again, and an exhaustive search of most of the rooms in the apartment comes up empty, but something keeps eating the cat food. Thus, we have concluded there's a cat in the apartment... but nobody has actually ever seen the cat.
#fuckbeta #iamslashdot #dicemustdie
My bet is that the need for dark matter will disappear when relativistic effects are properly taken into account.
There seems to be the belief among astrophysicists that general relativity can be safely ignored when speeds are low. I'm not so sure.
Anyone that can integrate knows large values can be obtained when summing even the smallest values. Perhaps billions of otherwise ignorable relativistic effects become a large effect when acting together.
It can't collide with itself? Good to know that the Majorana versus Dirac particle question is settled then. Oh, wait...
Of course, I didn't bother to RTFA...
Dark energy, the Ether of the 21st century.
I come here for the love
Or you could say space has a property of localized time. Which means time doesn't scale or progress uniformly throughout the universe. If you've got enough gravity, it's going to make things appear even more massive then they are because of time dilation. The relationship of gravity vs. time also means c should be treated as a coefficient rather than a constant. (The effective value of c still remains fixed, but that's because relationship of distance vs. time has both parts as variables. Time effectively rescales itself at higher energies to maintain c for a given distance traveled by a particle, but if you don't account for that, the extra momentum approaching or exceeding c looks like a gain in mass.)
Somebody with better math skills than myself could probably re-jigger Special Relativity in this regard and account for missing mass. It may even show a cumulative effect with gravitational time dilation when you have a system of multiple orbiting objects. But you might also have to toss the idea of a "Big Bang" out the window. (Makes "age" of things in the universe fairly irrelevant when a localized second is defined by the gravitational or acceleration field it's being measured under. Not to mention under certain conditions the typical light-year measuring stick astronomers like to use will also look about as uniform as a funhouse mirror. The funny-sounding Dr. Who sci-fi explanation of time being "Wibbly wobbly" may have some real logic to it.)
Of course it sounds nutty, because it opens up a lot of loopholes. Probably explains why Einstein was uncomfortable with some things, even if it provided the template for a more accurate model than some later revisions.
dark matter is the new aether
This is probably a dumb question, but I've been wondering about it for something like a decade, and I never see it referenced (even to debunk it) in legitimate science discussions.
A mysterious effect which looks like matter, but is invisible except for its gravitational effect. A second mysterious effect which causes the rate-of-expansion of the universe to increase.
I grow more and more skeptical of string theory and its relations every year, but the first of those definitely sounds to me like matter that's in another brane. The second one seems (to my non-physicist mind) like it could also be explained by the same thing, just a different set of matter in a different position relative to the first.
If our universe really is a 3D brane in a hyperdimensional space with others, isn't this exactly the sort of thing we'd expect to see? Further, wouldn't we see related effects like neutron stars unexpectedly flashing into black holes when they come into close-enough contact with dense clumps of matter in adjacent branes (IOW, when there's not enough observed mass in our own to explain the change to a black hole)?
"...always new atoms but always doing the same dance, remembering what the dance was yesterday." -Richard Feynman
"a diffuse mess, with a density that is ridiculously low, to the point where detecting its local effects is likely to remain... challenging for the foreseeable future"
In other word something irrelevant we can safely ignore and not invest any more money or resources into.
I haven't thought of anything clever to put here, but then again most of you haven't either.
That's correct. Only the priests of science have the right of thinking and conjecture.
If only people that have already done great things are allowed the opportunity to do great things, as all great things have obviously already been done by them, then the progress of civilization has already ended. I am glad that you are wrong.
This is a sig I've seen someone use on /. the article says to me dark matter was here, then nothing exploded.
The 2dF Galaxy Redshift Survey http://scienceblogs.com/startswithabang/files/2013/07/kozm_LSS.jpg
shows stuff coming towards us. I've heard so many space programs say everywhere you look everything is moving away from us,
They found that that the effects predicted on the basis of analogy with material science were not measurable.
But then came general relativity, quantum fields, dark energy, etc., and we decided an empty vacuum wasn't actually empty after all.
You've got a bit mixed up here. The entire idea of dark matter is because we can measure something we can't see - there are gravitational effects but not electromagnetic ones that have been seen yet.
It's more like stepping on a black cat in the dark. You've felt it underfoot for an instant and it's run off somewhere, so while you don't know what it is or where it is you do have empirical evidence that you've stood on something.
This may or may not relate to dark matter, but the other day, an electrical storm was passing over my house, and I momentarily saw a dark spot on the wall. Is there a scientific explanation for such phenomena? I've never had visual disturbances like that otherwise.
Y'know, Einstein himself once made the same mistake - called it the "cosmological constant" or some such. Needed a way to fudge his equations to jive with observed reality. I hear he was thrilled to hear 'bout Hubble's observations - made his equations work without nobtanium, unobtanium, adamantium, fudge factors, warp fudge factors or any other cheap cheats.
Mind you, I can't forward a better theory to explain why things have mass - but dark matter has always struck me as the modern equivalent of Russel's Teapot. Let me know when they find supporting evidence (which they may soon - or they may end up in the same place as Michelson and Morley).
...it can only be observed as a giant hole in our theory.
Having just finished watching Star Trek TNG Season 4 in lovely high definition, it appears that the effects of dark matter in the solar system will be A) Objects disappearing and reappearing at random, and B) A large increase in the amount of women wanting to date androids.
So, it can't collide with itself, meaning that it has no way of getting hotter[...]
Wouldn't gravitational interactions count as "colliding", at least for the purpose of exchanging energy? And the fact that it can't radiate away energy has more to do with it not interacting electromagnetically than its ability to collide with itself, hasn't it?
Let me know when they find supporting evidence [of dark matter]
You mean like the rotational curves of galaxies, the velocity dispersion of stars in galaxies (including observations of globular clusters with very little dark matter, leaving MOND with even more problems), gravitational lensing (including the bullet cluster), fluctuations in the cosmic microwave background etc.?
Mind you, I can't forward a better theory to explain why things have mass
Dark matter has nothing to do with why things have mass. That would be the Higgs field (or, rather, why fundamental particles have mass. Most of the mass of normal matter has another explanation).
Am I the only one who thinks about the Pioneer anomaly after reading this article?
If there is a constant density of dark matter in the solar system it will have a too small effect on Neptune to be detected. When moving further away from the sun the effect of the dark matter becomes stronger. So if we want to detect its gravitation we have to go as far away from the sun as possible. We should see something like the Pioneer anomaly, but we probably have to send a probe much farther out to detect any effect.
If dark matter is more prevalent than normal matter, then it would mean it is more stable than normal matter right? Maybe protons cannot decay into dark matter because there is no pathway for it. But in the high energy of the early universe, it must have been more common to chose the dark matter pathway than the proton pathway. So why isnt there large amounts of mass missing from the high energy collider experiments?