Does anyone else have a problem with the theory of Dark Matter/Dark Energy?

Question

Ok, here is how it works: we look at a galaxy though a big telescope.We measure the density of stars in different parts of the galaxy in question. Then we measure the doppler shift, and corresponding rotational speed for different areas of the galaxy.


Now we notice a real problem; the galaxy rotates too fast. In fact our theories predict that in order to rotate as fast as it does, our galazy needs to be twice as large, and have about ten times as much mass as we have just measured. Try as we may, we just cant account for the "missing mass."


Ok, no sweat, Its probably just an anomaly. So we measure the galaxy again with different equipment, we collect twice as much data. We measure lots of other galaxies. It's the same story everywhere, galaxies rotating way to fast, and we can't find any of the "missing mass".


Ok, so either our measurements are wrong, or our theory is wrong. But our theory can't be wrong! So all that extra matter must be there, we just can't find it!...

Thanks to all who answered.

Black holes, and planets might account for some, but not all of the "missing" mass. Neutrinos are also an attractive option, but the evidence there is sketchy at present. In my opinion, gravitational lensing is ambiguous evidence, since it could ether indicate the presence of DM, or simply emphasize the inadequacy of the current theory. With rotational measurements, and measurements of lensing, we are essentially measuring the same thing, the gravitational field, so lensing just tells us what we already know.

I might add tentatively, that since the N-body gravitation problem has yet to be solved, we have no way of knowing if our numerical models are totally accurate.

Answer 1

You are assuming that nobody has tried to make up another theory. In fact, the f(R) gravities have been proposed as alternatives, but they seem to be very ad hoc and don't have much independent support. People are actively working to find tests between such theories and that of dark matter.

The difficulty we face is finding an alternative theory that works in the solar system as well as the current theory *and also* explains the rotations of galaxies, the movement of galaxies in clusters, the gravitational lensing of galaxies, AND the evolution of galaxies at least as well as the cold dark matter theory. Remember that there are even several dark matter candidates (WIMPS, etc) from particle physics and the amount of dark matter needed for to explain several different lines of evidence is the same.

If you can come up with an other theory that is 1) well justified, 2) explains the solar system data, 3) explains the rotation curves of galaxies, 4) explains the containment of galaxies in clusters, 5) explains the amount of gravitational lensing from galaxies, 6) explains formaltion of galaxies and 7) does not have dark matter, PLEASE LET SOMEONE KNOW! The rotation curves are not the only piece of evidence for dark matter!

Answer 2

It is not a matter of the theory being wrong. We know that mass determines rotational rate. That's a law of physics. (this is called the virial theorum and states that the total kenetic energy of an object should be half the total of the gravatational binding energy) So unless you are postulating that the laws of physics are somehow nullified when we are talking about galactic rotation then the theory is sound. It is much more reasonable to assume that there is some missing mass.
In fact, recent studies seem to prove the existance of dark matter. Observations of gravatational lensing seem to prove that there is some invisible mass where scientist postulate dark matter to exist.
Of course, it is entirely possible that scientists are wrong. The dark matter/dark energy solution is only a theory to explain the given facts. Perhaps we will find a new fact that nullifies the theory. Science can only predict and conclude. It can't say "This is true". It can only say "this is likely".
So, the existance of dark matter, at this time, seems the most reasonable explination for the behaviour of matter in gravatational lensing and solves the "missing mass" problem as well.

Answer 3

Well, I don't so much have a problem with either theory so much as I feel (and am probably correct in feeling) that there's more to the situation. After all, we don't know what dark matter or dark energy are. In some sense, they're placeholders for explanations which we'll eventually find for observations which we have made and confirmed pretty well. There are lots of unanswered questions about both concepts, and I think that the answers we find will be very interesting. In that sense I "have a problem" or more accurately am not satisfied with the current state of the theories regarding dark matter and dark energy.

Answer 4

Dark matter and dark energy have been encorporated into the standard model for cosmology, and this model is being extensively checked out. There are several ways that DM/DE can manifest themselves in detailed observations, and these observations are being done in order to see whether the standard model holds up or not.

One type of sensitive observation is gravitational lensing from Dark Matter concentrations. The distribution of Dark Matter is (or should be) clumpy in ways that can be predicted. This will result in gravitational lensing of background objects, in well-defined ways that can be checked in detail against observations.

Another type of observation relates to the statistics of clusters of galaxies. How many clusters of galaxies, of what size and internal velocity dispersion is sensitive to the properties of both DE and DM. Complete surveys for galaxy clusters are underway, and can be compared to predictions from the standard model.

If there are deviations from the Standard Model, perhaps we can invent a theory that seems more attractive. Alternatively, we may come to understand fundamental physics in a way that makes DM/DE seem more natural.

Answer 5

Dark matter is what scientists call all the stuff in the universe that they know is there but can't find! they think it might be made of ghostly little particles called neutrinos. Scientists can guess how much matter is in the universe by measuring how galaxies move. This shows them that stars and planets only make up a small part of the Universe. The rest is invisible!

Answer 6

Ok...
Here's where it gets technical.
Everyone knows black holes, right?
They are formed from supernovas.
These supernovas are caused by giant stars 10,000 times as big as our sun, dwarfing us to litereally nothing.
Then there are these "super" black holes. They range from between 100,000,000 times to 1,000,000,000 times the mass of out sun. How did they get here?? The fact is, noone knows. They were supposedly formed by lots of regular black holes in the early universe, supporting the big bang theory. Anyways I'm also a supporter of the theory that black holes are at the center of all galaxies. Now, some super black holes have gone dorment, although they may start feeding again. So what I'm getting at is that there is really no missing mass, it's just so compacted that it's gravitational force is so strong that it's escape velocity is over 186,000 miles per second, aka the speed of light. The hubble telescope can't see this monster because light is getting made to be "dark" (and I use the term loosely) energy so it can't rebound and give us an image. And even though it is monstrously huge the universe is a big place and we are on the outer edge of the galaxy, and we're not going to get any closer until the monser starts feeding again, which will ultimately lead to our demise.


Have a happy day!:)

Answer 7

Every place else we test the theory it predicts reality. That includes the gravitational attraction between galaxies and groups of galaxies, solar systems etc. Why should we doubt the theory when applied to the rotation of galaxies ? Is there something unique about the space inside them? I have no problem with the concept of dark matter.

Answer 8

I have a problem with it. To me it feels like the argument for eather. This mysterious matter that we don't know about, but we know it exist. To me it sounds like they are not willing to think that the calculations or prior studies can be wrong, so it must be some mysterious element.
IT seems to me like they invented this stuff to cover up a lack of understanding of the universe. I would rather hear. "we don't know." Then a lot of garbage about mysterious stuff that can't be tested so far.
B

Answer 9

That's the basic idea, yes. The theory works just fine in all other cases, and there's no reason for it not to work in this one, so we're missing something - like a lot of matter.

What exactly is your problem with it? I'm not clear as to what your question is.

Answer 10

just like the only word you forgot to use in what you said is the fact that they cant see or measure planets that far awaywould make it hard to include the data they represent they have mass and gravity they dont shine and they effect the orbital speed of other planets and there satilites so there it is dark matter is planets