Hubble Survey Finds Half of the Missing Matter

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

[Anonymous Coward]

I knew someone was going to make an ether comment. The luminiferous ether was the hypothecial medium that electromagnetic waves (including light) traveled through. It was hypothesized because, at the time, there were no known waves that traveled without a medium. However, the ether was disproven, and it was shown that EM waves travel without a medium. What's mentioned in the article is not ether.

Re:Dark Matter???

[CheshireCatCO]

This isn't dark matter. Dark matter shows evidence (based on its measured distribution) which is not consistent with ordinary baryonic matter.

Re:Dark Matter???

[Btarlinian]

Always wondered why a simple explanation like dust never took hold, and everyone started talking about invisible matter to explain what should be there.

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???

[JebusIsLord]

No, it says we've been missing ionized hydrogen and helium within a certain temperature range. How about reading the article before posting next time?

Re:Dark Matter???

[Tenebrousedge]

Well, dust is not dark matter. There's other matter besides baryonic matter. There's a great picture on wikipedia that 'shows' dark matter. The debate on dark matter is how much it exists and its exact nature, not whether it exists.

Re:Dark Matter???

[omnichad]

Poor neutron...

Re:Dark Matter???

[Chris Burke]

More things that were supposed to be dark matter that turned out to be pretty ordinary matter.

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

[naasking]

Wouldn't it make more sense to go with an aether theory? [...] How about gravity increasing the optical density of the aether?

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

[ChrisA90278]

What was found here was missing __baryonic matter__ the bigger question is still unanswered. Bryonic matter is the normal stuff we are made of but most of the "stuff" in the universe is non-baryonic and still "missing".

Re:Ether

[lgw]

Well, if you assume that the Earth moves through such a medium as it orbits the Sun, you can look for that, as you can tell there's a medium when you move relative to it - which was the Michelson-Morley experiment [virginia.edu].

Re:Ether

[hardburn]

The universe likely has neutral charge [ucolick.org]. Also see a more detailed discussion [physicsforums.com] on the subject.

Re:Ether

[hardburn]

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

[TropicalCoder]

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

[EPAstor]

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

[BZ]

Wave function collapse is a much more controversial thing than the existence or non-existence of the ether. Basically, it's the only non-unitary, non-differentiable, discontinuous part of quantum mechanics. Oh, and it violates special relativity, though that might count for less given the topic of discussion here. There are various suggestions (such as many-worlds theories) that might avoid the need for this artificial wavefunction collapse altogether.

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???

[shma]

Cosmologists use the term 'dust' to refer collectively to non-relativistic matter in the early universe.

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

[khayman80]

Not exactly... The MM experiment predicted a phase shift when the optics table was rotated. It wasn't time-dependent. The phase shifts expected by LIGO/LISA are sporadic events that should only be sensitive to huge events such as black hole creation or neutron star mergers. They won't vary with the orientation of the plane of the interferometer, and they won't be constant in time either.

Re:Had it been a snake...

[Chris Burke]

Um, why wasn't the entire EM spectrum scanned across the heavens instead of "discrete" well-known segments like radio, x-ray, visible, IR, UV, etc.? Is it a money and time issue? Otherwise it seems that this should have been found decades ago.

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

[GanjaManja]

(actually, they mention that regular matter is not detected via gravitational effects, they simply observed the absorption spectrum. However, when the gasses are highgly ionized, there are no electrons spinning around waiting to absorb the light, and thus the ionized Hydrogen does not yield an easily detectable absorption. (see 2nd article) "dark matter", non-regular matter, is detected via the gravitational lensing effects. )

Re:Ether

[orangesquid]

I'm taking a grad-level course in optical properties of condensed matter, and one of the things we study is how EM propagation is slowed by atomic dipole formation in polarization from photonic fields. It would be interesting if it were the case that the vacuum could be demonstrated to have, at the quantum level, some degree of spontaneous polarization in a field, and since there's always a field (even if perhaps self-induced from uncertainty foam), you could somehow make an analogy to the concept of the aether (even though it would not have the properties of the aether). However, as far as I've studied, that's not the case, because you can't ever rid yourself of QHO's unless you have a universe with no net matter/energy (which we don't have, even if you are looking at a gauge symmetry), no uncertainty principle (but matter waves obviously exist, because you can even diffract molecules), or you can demonstrate that QM is based a flawed assumption, viz. that matter waves don't extend to infinity (but experiments with entanglement have demonstrated that assumption to be accurate to a very high degree). Of course, we don't have a solid definition of what exactly constitutes an observer, but as far as formalism is concerned, most of our results don't need one.

And, yep, I *am* talking out my ass ;). No, actually, if it weren't early in the morning, and I weren't busy working on other things, I would go back and make the above paragraph (a) cite references, (b) use accurate and proper terminology rather than vague concepts, and (c) convey my thoughts with some rigor instead of a bunch of conjecturous statements.