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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."
As opposed to the ether of the 19th century, quantum fields, which are what we currently use to explain everything?
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.
But we do find it empirically. There is extra mass there, affecting other objects. We can detect it through it's gravitation, just not through light. It's a very strong signal, for example in the rotation velocity of galaxies. A lot of other science is, too, done without directly detecting the object of study, but through indirect effects and inference.
Everyone would like to get rid of Dark Matter. But its effects are clearly there. And we need to explain it. It does not have to be particles, or a kind of matter we know. You can call it something else than Dark Matter if you don't like the name. Anyone is welcome to come up with explanations. But they have to be in agreement with the observations.
NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
My bet is that the need for dark matter will disappear when relativistic effects are properly taken into account.
And I bet that at some point during the last few decades of thousands of observations, theories, and calculations by thousands of astronomers, physicists, and mathematicians (some with Nobel prizes, no less), someone would have already thought of this if it was an issue.
systemd is Roko's Basilisk.
Why invent exotic matter when the right combination of dust could be the answer?
Simply put, because baryonic matter (ie. dust) radiates. This article would be titled, "Why our instruments are sensitive enough to detect all that dust that's affecting galaxies and superclusters rotation" if it was dust.
Here's a recent summary paper on the evidence for nonbaryonic dark matter. Dust has, alas, been hypothesized, tested, and rejected.
E pluribus unum
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
Are you describing tentacle porn?
Learn to love Alaska
That's because when you say things like that you check off quite a few boxes on the crackpot criteria.
It's not a religion. Lots of different dark matter theories and alternatives have been proposed and tested. The problem is that when some random Slashdotter comes along and says "dude, it must be something else!" the actual astronomers, and the amateurs who can read, roll their eyes. When the same Slashdotter then says "dude, you're not taking me seriously because you can't get past your religious dogma!" said astronomers and literate amateurs roll their eyes harder.
Planets are just clumps of dust.
But clumps of dust with a really low surface area for the mass involved. For example, Jupiter has a density of 1,330 kg per square meter and an average radius of almost 70,000 km (7*10^7 meters), a third more than water at STP. If instead, Jupiter were broken up into many equally sized balls of a smaller radius, then the mass stays the same, but the increase in surface area is inversely proportional to the decrease in radius.
For example a Jupiter-mass cloud of micron sized spheres, each with the density of Jupiter, would have a surface area 7*10^13 larger than Jupiter. That surface area incidentally happens to be roughly a twentieth of a square light year (roughly 4*10^30 square meters by my calculation) meaning at the right densities, such a cloud could intercept and radiate a lot more energy than Jupiter could, perhaps even be visible in small amateur telescopes at a few lightyears.
My point here is that some baryonic matter is a lot more visible, many orders of magnitude more visible, than other baryonic matter. And planet-sized objects are going to interact mostly by gravity as well meeting most of the desired characteristics of dark matter.
My take is having a significantly higher than expected fraction of the mass of your galaxies in rogue planets and similar things would be a way to account for dark matter.
But then there's the early universe observations. For example, the most damning evidence against dark matter hiding in planets and such, is observations of the cosmic microwave background (CMB), which is effectively the study of the period of the universe in which it started to become transparent to photons (about 400k years after the big bang according to the above link). That period of time is not a lot of time in which to create massive objects. And the fluctuations of the CMB yield dark to visible mass of roughly 5 to 1 (again according to claims in the above link).
So that indicates to me that there probably some sort of exotic matter out there which we haven't discovered yet.
You mean how this stuff is 100% transparent to all known frequencies from radio to gamma? Please, tell me what matter you know of that is 100% transparent to all forms of radiation. Enlighten us all knowing one.
Yes, we know, 100% that is is transparent. There are HUGE spots in the sky where there is gravitational lensing affecting background galaxies, but no obstructions in front of the galaxies. Something is causing the gravity, but it is letting the background light through perfectly clearly, minus the lensing.
We're not talking about small amounts of gravity either, whole galaxy masses worth. If you had a galaxy worth of gravitational lensing, you'd hope to find something causing it. Instead the background light comes through crystal clear, like nothing is there.. hmmmm...
Ah, I understand. You're talking about people who are skeptical of your favourite off the wall theory. That's not religion. As the thread before your post said, when Slashdotter 214243 comes along with some theory from left field, along with an assertion that the experts (some of whom have Nobel prizes), who have put careers into looking into this question, are wrong (or religious), he better have some good evidence to support it. Every time I've seen it that "evidence" boiled down to a vague, usually incorrect understanding, usually with a healthy dose of conspiracy theory.
Maybe you've seen something a little more solid? Care to share?
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).