Is dark matter hiding in plain sight?

[Garth]

Thank you, I await the discovery of the WIMP DM candidate particle with anticipation!

As far as the last point is concerned, shouldn't it be the other way round? Do not the heavier haloes have increased star formation as a proportion of total mass? (According to the Baryons and Their Halos paper.)

Garth

 

[mintparasol]

OK, I won't even pretend that I understand any of the math in this! My understanding of this is gleaned from high school physics (15 years ago) and a healthy interest in pop. science. Dark matter, or the notion of it, seems a bit like the emperor's new clothes to me. We can never say for sure how the universe we inhabit came to be. Sure, we can extrapolate by inputting observational data to extremely detailed and rigorous mathematical models what may have occurred in the very distant past but direct knowledge of it is clearly impossible. It seems to me that the unpredictable gravitational curves around massive galaxies could be caused by anything. The lensing and other observed effects which led to the postulation of dark matter may even be a property of spacetime itself, some as yet undetected property of a field or 'brane'.
Matter that is completely electromagnetically null? I'm not sold on this one...

 

[Ich]

Matter that is completely electromagnetically null? I'm not sold on this one...

Well, then brace yourself for learning about http://en.wikipedia.org/wiki/Neutrino" .

emperor's new clothes

No, please. If you follow the discussions here, you'll find out why people believe that there is something more.
If it looks like cloth and feels like cloth, you'll go ahead with the preliminary assumption that the emperor is not naked.
If it turns out that he is naked: good bodypainting, and nothing one could have foreseen from pop sci.

 

[twofish-quant]

Dark matter, or the notion of it, seems a bit like the emperor's new clothes to me.

Dark matter and dark energy reminds me of 19th century "ether", and there is a lot of stuff out there that is just screaming that we are all missing something fundamental. But I can't think of anything, lots of smart people are working on the problem, and they can't think of anything better. More data, more stumbling around in the dark, and eventually we'll figure something out.

We can never say for sure how the universe we inhabit came to be. Sure, we can extrapolate by inputting observational data to extremely detailed and rigorous mathematical models what may have occurred in the very distant past but direct knowledge of it is clearly impossible.

On the other hand, direct knowledge of anything is really impossible. I have this memory of being on the subway this morning. It could have been an illusion, and I could be in this giant matrix. Trying to figure out what happened 13 billion years ago, isn't all that much different from trying to figure out what happened this morning.

Also the models aren't that detailed and they certainly aren't very rigorous.

It seems to me that the unpredictable gravitational curves around massive galaxies could be caused by anything.

They can't be caused by *anything*. For example they can't be caused by non-dark matter since if it was caused by non-dark matter, we would have seen it. You eliminate what it can't be, then you try to make some sense about what it can be.

The lensing and other observed effects which led to the postulation of dark matter may even be a property of spacetime itself, some as yet undetected property of a field or 'brane'.

Maybe. At that point you go with that idea can then put limits on the properties of space time that it can't be.

Matter that is completely electromagnetically null? I'm not sold on this one...

Neutrons are electromagnetically null.

 

[mintparasol]

Neutrons are electromagnetically null.

They are detectable though, right? What's bugging me about dark matter is that it has never been directly detected, only postulated by inference.

 

[DaveC426913]

They are detectable though, right?

Sure, now. They were postulated long before their existence was confirmed. It was the postulation that led to the search that led to the discovery.

 

[twofish-quant]

Sure, now. They were postulated long before their existence was confirmed. It was the postulation that led to the search that led to the discovery.

Same for protons, neutrons, neutrinos, and electrons. For that matter *not* finding something is sometimes as interesting as finding things. It turns out that ether, Vulcan, and "Planet X" (a planet beyond Neptune that was influencing orbits) all didn't exist, but looking for them was useful.

There's a lot about dark matter that bothers me (and even more about the Higgs field that bothers me), but physics advanced by looking for things and either finding or not finding things. Personally I'm hoping that they run LIGO and LHC for a few years and find absolutely *nothing*, because finding nothing would require quite a bit of theoretical effort to explain why nothing was found.

We are just guessing and stumbling around in the dark which is what makes the business interesting.

 

[mintparasol]

Sure, now. They were postulated long before their existence was confirmed. It was the postulation that led to the search that led to the discovery.

Same for protons, neutrons, neutrinos, and electrons. For that matter *not* finding something is sometimes as interesting as finding things. It turns out that ether, Vulcan, and "Planet X" (a planet beyond Neptune that was influencing orbits) all didn't exist, but looking for them was useful.

There's a lot about dark matter that bothers me (and even more about the Higgs field that bothers me), but physics advanced by looking for things and either finding or not finding things. Personally I'm hoping that they run LIGO and LHC for a few years and find absolutely *nothing*, because finding nothing would require quite a bit of theoretical effort to explain why nothing was found.

We are just guessing and stumbling around in the dark which is what makes the business interesting.

Well, I can't argue with either of those replies! Thanks to yourselves and to everyone who replied. It's kind of cool that a question from someone like myself who knows virtually nothing about the technical aspect of physics can get such a lively debate going.
Thanks again, I think I'm returning to my belief from when I first came on here nearly a year ago that gravity has something to do with neutrons or neutrinos...
Regarding dark matter - is there any sign of it in our locality? Like somewhere near enough that a probe we send could arrive and collect data within our lifetimes?

 

[twofish-quant]

Thanks again, I think I'm returning to my belief from when I first came on here nearly a year ago that gravity has something to do with neutrons or neutrinos...

It probably does. It's figuring out exactly what and how that gives people headaches.

Regarding dark matter - is there any sign of it in our locality? Like somewhere near enough that a probe we send could arrive and collect data within our lifetimes?

If dark matter turns out to be made of weak interacting massive particles, then we are swimming in the stuff. Given reasonable numbers, we are looking at 100,000 dark matter particles passing through every square centimeter of Earth every second, and yes people are trying to find them...

http://arxiv.org/abs/0906.5361

https://physicslearning2.colorado.edu/tasi/tasi_2009/Attachments/Schnee_02_200906SchneeTASI2opt.pdf

http://www.astro.caltech.edu/~george/ay20/eaa-wimps-machos.pdf

This is the really interesting thing. It could be that tomorrow someone could publish a paper saying "YES WE FOUND IT", or it's possible that people could be running the experiments for the next million years and find nothing because there is nothing to find.

But in physics, looking for something and not finding it is important, because every month that goes by in which people look for dark matter particles and don't find anything, puts new limits on what is possible and what isn't. One of the most important null results was Michelson-Morley in which they tried to observe the Earth's passage through ether and found nothing. Proton decay is another important null experiment.

But there are also examples where you detect nothing, but there is something there. One of my favorite examples of this are the neutrino beam experiments at Fermilab. There is a beam there that generates massive numbers of neutrinos which then go through Wisconsin to hit a target in Minnesota.

http://www.sciencedaily.com/releases/2005/03/050325231252.htm