Slashdot Log In
The Search for Dark Matter and Dark Energy
Posted by
ScuttleMonkey
on Mon Mar 12, 2007 06:34 PM
from the someone-needs-to-turn-on-a-light dept.
from the someone-needs-to-turn-on-a-light dept.
mlimber writes "The New York Times Magazine has a lengthy article on dark matter and dark energy, discussing the past, present, and future. 'Astronomers now realize that dark matter probably involves matter that is nonbaryonic ["meaning that it doesn't consist of the protons and neutrons of 'normal' matter"]. And whatever it is that dark energy involves, we know it's not 'normal,' either. In that case, maybe this next round of evidence will have to be not only beyond anything we know but also beyond anything we know how to know.'"
This discussion has been archived.
No new comments can be posted.
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
Full
Abbreviated
Hidden
Loading... please wait.
Knowing Know (Score:5, Funny)
Re:Knowing Know (Score:5, Funny)
>
> I knew he was going to say that.
As long as we're quoting Rumsfeld, "You do high-energy physics with the particle accelerators you have. It's not the particle accelerator you might want or wish to be able to build at a later time."
Parent
Can dark matter just be.. (Score:5, Interesting)
..."in-transit" energy from 100,000,000,000 stars?
...large amounts of completely non-reflective dust and asteroids?
...a side effect of over-estimating the size of the universe? (i.e. stars like our 5 billions light years away don't exist anymore)
/real questions
//just curious..
Re:Can dark matter just be.. (Score:5, Informative)
The 'size' of the universe is an ill-defined question. We can only observe what's in our past light cone, and it is *that* universe which suffers from a budget shortfall of matter/energy.
Parent
Re:Can dark matter just be.. (Score:5, Informative)
Galactic dark matter, which is required to explain the rotation curves of spiral galaxies, can be completely explained by baryonic dark matter, which would be at least partially dust.
Extra-galactic dark matter cannot be primarily baryonic. The baryon density of the universe is known from big bang nucleo-synthesis and the primordial H/He ratio, and is too small to account for extra-galactic dark matter. Therefore extra-galactic dark matter has no relation at all to galactic dark matter, as it cannot be made of the same stuff as galactic dark matter.
So there are at least two completely different, totally unrelated dark matter problems. One can and probably is solved by baryons. The other requires exotic particles or possibly exotic physics.
Parent
Re: (Score:3, Interesting)
You're right that the universal baryon density doesn't specifically constrain galactic dark matter. But Occam's Razor suggests there is only one dark matter problem. Besides, you would have to explain why galaxies would have one type of dark matter while galaxy clusters have a completely different kind (and we know intra-cluster dark matter is non baryonic). It's much easier to explain the dark matter evidence at all s
Re:Can dark matter just be.. (Score:5, Informative)
Parent
Dark Matter Exists (Score:5, Informative)
Here [cosmicvariance.com] is an excellent article by Sean Carroll [preposterousuniverse.com] of the California institute of Technology that explains why all the suggestions of the parent post may not be correct.
Basically, what it says is that if two large clusters of galaxies went right through each other, and dark matter was really like the normal matter in the way the parent post suggests, we would get a different result from what would happen if dark matter was for real. Astronomers have discovered one such system and this provides conclusive evidence for the existence of dark matter.
Parent
How about ... (Score:5, Insightful)
Not really... (Score:5, Insightful)
Parent
Re:Not really... (Score:5, Insightful)
You better tell John Moffat that very large bodies are extremely well-approximated by Newton so he can stop wasting his time on Tensor-Vector-Scalar [wikipedia.org] gravity.
Dark matter seems like far from settled science to me. But it always does amaze me how dark matter proponents tend to treat it's existence just like the followers of intelligent design treat God.
Parent
Re: (Score:3, Interesting)
Nothing to see here... (Score:5, Funny)
Re: (Score:3)
Dammit (Score:2)
I think this might be one of those things I chose not to learn and just leave to someone else.
Dazzling (Score:4, Funny)
That's an educated opinion, if I've ever heard one.
"Normal?" (Score:5, Insightful)
Re: (Score:3, Insightful)
Re:Telescopes invented 400 years ago? (Score:5, Informative)
I didn't know telecopes were that old. Is this a typo, and didn't they mean decades instead? If not, what did ancient telescopes do?
FooBarWidget, meet Galileo: Widely credited as the inventor of the modern telescope, in 1609.
Though, as with all major developments in human history, some accounts have him as merely improving on preexisting tech, whether copying the work of Lippershey from 40 years before, or even the possibly MUCH older designs of the ancient Persians.
So no, not a typo.
Parent
Re: (Score:3, Insightful)
One big take home point about dark matter and dark energy is that physicists didn't want them to be true! It took an enormous amount of evidence, with countless independent confirmat
Send them to the Randi foundation, then (Score:5, Insightful)
Heh. Well, then, just send them to the Randi foundation which still has a 1 million dollar prize for anyone who can prove anything like that. The requirements so far have been reasonable too, usually along the lines of having a scientific double-blind test. Nothing you wouldn't expect in normal science. Altering probabilities is even more straightforward, since then you just have to take a large enough sample and do some elementary statistics. So you'd think that if ESP or mind-over-matter or whatever floats your fantasy boat was that proven and working, someone would claim the prize already. But, nah, suspiciously so far what we've had were:
- bullshitters arguing about how unsound scientific testing is, and why they won't take part in it (sorry, if something is only perceived when the test subjects are told and persuaded what they should perceive, then it's probably just make-belief.)
- lame stage magician tricks
- various versions of some global conspiracy to suppress them (funny how noone suppressed them before, then. You'd think the conspiracy would then stop them from publishing books and making faked movies about it too, not just stop them from taking part in a controlled experiment.)
Etc.
Plus, Randi isn't the only one who came up empty so far. What fraudsters are quick to tell you, as if it were some proof of ESP existing, is that both the USA and the USSR were interested in it during the cold war. That much is true. Unsurprisingly, since for example transmitting a message to a submarine by a mean that's (A) not blocked by water or rock, hence receivable from any depth or hole, and (B) impossible to intercept, is any army's or navy's wet dream. What they conveniently ommit there is that both the USA and the USSR, and a few others for that matter, failed to get any results with it.
By contrast, the people with these physics hypotheses tend to actually have some verifiable/falsifiable data, and they give it to you up front. If they did just bullshitting and handwaving like the ESP gang, we wouldn't take them seriously either.
Parent
Re:Questions from a B- physics student (Score:4, Informative)
This could all be accounted for by dark matter save for the observations of Type 1A supernovae which indicate accelerating expansion, and this requires domination by a state of matter with negative pressure, and this is what's been coined dark energy.
Parent
Re: (Score:3, Insightful)
That is all well and good but it may be that the need for "dark energy" and "dark matter" may be the result of sloppy science. If scientists cannot tell the difference between a distant giant galaxy and a nearby dwarf galaxy, how can you believe a word they say about missing mass?
Doesn't this article quite clearly show that people can tell the difference, however for this particular galaxy (presumably unremarkable and not very well observed, given that apparently nobody has taken a measurement of the red-shift for the past two decades) someone messed up and they were treated using incorrect data?
Mistakes happen in all fields, to say that one particular example (or, indeed, given the human capacity to screw up, numerous ones) renders a field meaningless is highly dubious. What is
Re: (Score:3, Informative)
http://en.wikipedia.org/wiki/Black_hole#Black_hol
GR does not work at Galactic Levels (Score:3, Informative)
The real problem is MOND. If it did not exist then Dark Matter would be free to exist wherever it wanted. But with MOND the picture becomes more complex, now DM must fit MOND. It is quite easily provable that DM cannot fit MOND, just apply it to small cluster of stars at the outer edge of Milky Way which show Dark Matter. The problem is that for DM to fit Milky Way, it cannot be present in the Clusters. But some