Hubble Survey Finds Half of the Missing Matter 189
esocid sends along the news that scientists believe they have found about half the missing matter in the universe. The matter we can see is only about 1/8 of the total baryonic matter believed to exist (and only 1/200 the mass-energy of the visible universe). This missing matter is not to be confused with "dark matter," which is thought to be non-baryonic. The missing stuff has been found in the intergalactic medium that extends essentially throughout all of space, from just outside our galaxy to the most distant regions of space. "'We think we are seeing the strands of a web-like structure that forms the backbone of the universe,' Mike Shull of the University of Colorado explained. 'What we are confirming in detail is that intergalactic space, which intuitively might seem to be empty, is in fact the reservoir for most of the normal, baryonic matter in the universe.'"
Re:Ether (Score:5, Informative)
Re:Dark Matter??? (Score:5, Informative)
Re:Dark Matter??? (Score:5, Informative)
We know that there is some sort of matter missing due to weird graviational interactions. We also know that according our measurements of the cosmic microwave background, this matter doesn't exist, i.e., this matter doesn't interact with electromagnetic fields. That's why it's not normal baryonic matter.
Therefore, we say that there must be dark matter. Plain old dust would have showed up in our readings of the CMB.
Re:Dark Matter??? (Score:3, Informative)
Re:Dark Matter??? (Score:4, Informative)
Re:Dark Matter??? (Score:2, Informative)
Re:Dark Matter??? (Score:5, Informative)
No, that's not true. We already knew there was "ordinary" matter we hadn't found, we knew it wasn't "dark" matter, we just didn't know where it was. Now we found a bunch of it.
Re:Ether (Score:5, Informative)
The problem with ether theories is mainly the Michelson-Morley experiment. Are there ether theories which avoid the MM pitfall? Sort of. The Polarizable Vacuum [wikipedia.org] (PV) is a very interesting theory along the lines of what the the above poster suggested. Instead of matter bending some mysterious "ether", as in ether theories, or bending space-time, as in relativity, matter instead affects the electric and magnetic permeability of space, which causes light to behave as if it were passing through a medium with a higher dialectric constant. From that simple assumption, we can almost rederive full general relativity (GR) wherein electromagnetic equations produce gravitational effects. Gravity is electromagnetism! PV has since been disproven, but it's still a stunningly simple way to think about gravitation in terms of electromagnetism.
Re:Wow (Score:3, Informative)
Re:Ether (Score:3, Informative)
Re:Ether (Score:4, Informative)
The universe likely has neutral charge [ucolick.org]. Also see a more detailed discussion [physicsforums.com] on the subject.
Re:Ether (Score:2, Informative)
Michelson-Morley was an important part of it, but it was Einstein that finally killed it off by proving that waves and particles aren't as seperate as they appear to be, and thus ether is unnecessary. A few stodgy professors hung on for a while, but they eventually retired/died off without convincing very many of their students.
Re:Ether (Score:5, Informative)
Thanks! I found the answer, and read some very interesting discussion in the links you provided. Interesting that though I have been reading about physics and astronomy for many years, I have never run into this kind of discussion before...
"The electromagnetic force is so strong that if the universe had even a slight net charge, electric and magnetic fields should dominate the structure of our universe. But it doesn't -- gravity does. And gravity, believe it or not, is a very weak force. There are other effects that electric and magnetic fields would have on light, and we simply do not see these effects."
"If a gas in ionized it simply means that some electrons have separated from the constituent atoms (or molecules) that make up the gas leaving positively charged atoms/molecules and negatively charged electron. However they are still mixed together in the same gas, the 'separation' that you assume does not exist. The positive and negative charges still mingle in the same space. Even if you took a very small volume (the size of a grain of sand) of an ionized gas the overall charge is still neutral."
Re: Ether (Score:4, Informative)
It's not quite like that... Quantum states' collapse is barely real in the sense that we know it. In particular, it doesn't carry information - so the experiments we already have, which indicate that what we call collapse is a non-local phenomenon (carries faster than the speed of light, possibly instantly), don't contradict special relativity.
Yes, you read correctly - to all our best measurements, collapse appears instantaneous, not like a propagating change in a wave.
Re:Ether (Score:3, Informative)
Back to the topic at hand, the interesting thing with special relativity is that while it was created based on the results of the Michelson-Morley experiment, it doesn't actually "explain" that experiment. It just assumes the results of that experiment, somewhat generalized (light travels at the same rate in all inertial reference frames), and then makes a wide variety of predictions that differ wildly from Newtonian mechanics, have been verified experimentally, and have nothing to do with electromagnetism (and thus are not likely to have to do with the ether).
The two obvious examples:
* Predictions about things like energies required to accelerate a given
mass to a given speed. If the speed is a significant fraction of
3*10^8 m/s, the predictions are very different from the Newtonian
ones, and the special-relativistic predictions match experiment.
* Predictions about time-dilation. There is a very interesting
experiment one can do using the Mossbauer effect (in iron, say). The
width of the absorption line for gamma rays in the iron nucleus is
very small, so that one can measure doppler-shifts on the order of
10^{-13} of the gamma ray frequency. That turns out to be sensitive
enough that if you have two samples of iron at somewhat different
temperatures easily producible in the lab (somewhat below 0 C and
close to 100 C, say) the gamma rays absorbed by one sample are NOT
absorbed by the other one. By moving one of the samples to introduce
a doppler shift, one can find the exact amount of the frequency shift.
If you then try to account for this frequency shift, it very closely
matches the prediction one gets by applying special-relativistic
time-dilation due to their thermal motion to the iron atoms. I
haven't seen a decent alternate explanation for the results of this
experiment.
I'm not sure I've seen a decent explanation of either of those in terms of things like frame dragging...
Re:Dark Matter??? (Score:4, Informative)
In the most basic big bang model, there are only two kinds of matter which we consider: 'dust' and 'radiation'. All non-relativistic matter is treated as a pressureless fluid which we call 'dust', while all relativistic matter is lumped together as 'radiation' and treated as an ultralativistic fluid: one whose kinetic energy is so great that its rest energy is only a small correction to its total energy, and can be neglected (so we can treat them as if they were massless photons).
These definitions aren't used outside of cosmology, so generally you won't hear about them in this context.
Re:Ether (Score:4, Informative)
Re:Had it been a snake... (Score:4, Informative)
Because different wavelengths require different technologies to detect. Like to detect visible wavelengths you use big mirrors and/or lenses, while to detect radio waves you use antennas, and so forth. It's not as simple as "scanning" the entire spectrum.
Re:Wow (Score:2, Informative)
Re:Ether (Score:3, Informative)
And, yep, I *am* talking out my ass