Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum LHC latest on Dark Matter

Tommasso has posted a really well written look at the latest results in the look for Dark Matter from CERN which is well worth the read.

http://www.science20.com/a_quantum_diaries_survivor/no_light_dark_matter_in_atlas_search-147043

Dark matter still very much a no show and I loved his take home quote which will get some cosmologist hot under the collar no doubt Quote: "As attractive as DM existence is as an economical explanation of a wealth of cosmological observations, the nature of dark matter continues to remain unknown."

"As attractive as DM existence is as an economical explanation of a wealth of cosmological observations, the nature of dark matter continues to remain unknown."

I imaging that could be applied to dark energy as well.

This probably belongs in this thread. I missed this one, as it's not my thing, but good pickup and analysis by Adam Falkowski.

http://resonaances.blogspot.com.au/2014/11/weekend-plot-fermi-and-7-dwarfs.html

Sorry I missed that question Bill S and again I stress this is not my thing so I shall interpret the current dark matter FAQ for you as best I can.

Dark matter is an attempt to explain observational error between the gravitational mass and the luminous mass of galaxies and clusters. So you have GR calculations pitted against luminous mass using nuclear physics of how suns work and there is disagreement. So the solution to reconcile the difference is to have a new particle that has escaped detection during particle accelerator experiments and cosmic ray experiments.

So the resolution to the above comes down to what you "trust". If you asked me for a personal janitor view I would trust GR, especially on these scales, and cast doubt on everything else in that argument and be looking hard at it.

Dark energy comes from the discovery that the universe is expanding; it isn't directly related to Dark matter and they can't easily be joined although layman do. Dark matter would pull the universe together like normal matter. Dark energy is needed to push the universe apart or at least account for the energy.

Now dark energy is on a somewhat more solid ground than dark matter with current experiments. Ethan actually did a really good write up on it from a cosmological point of view here showing that it has 3 theories all predicting it

https://medium.com/starts-with-a-bang/ask-ethan-58-what-is-dark-energy-61db04945b3d

Distilling what he is saying for you it goes like this GR says that if the vacuum has energy density it must also have pressure. The pressure is equal to exactly -1 times its energy density, in units where the speed of light and Newton's gravitational constant which you set as equal to 1. Positive energy density expands the universe, negative energy density contracts the universe. That view is consistent with all cosmological data and experiments.

That view can be consistent with QM or not depending on how you reconcile some basic structural things. If you asked me for a personal janitor view I would say I think that QM is saying the same thing in the vacuum energy density in quantum field theory, but it would be contested by others.

Thanks Orac. A point arising out of Ethan's article is that as the Universe expands "the energy density of dark energy doesn’t decrease". This must mean that dark energy is constantly being created. How can this be justified in terms of conservation of energy?

You can conserve energy if you turn energy just into an accounting process, so that it plays the same roll as currency in economics and use cosmology science

Ethan shows that approach nicely in an earlier article
http://scienceblogs.com/startswithabang/2011/12/02/dark-energy-accelerated-expans/

It's a nice story unfortunately it's only true in cosmology to a target audience, Bill G would love it

Let me show you the problem using the positive side of that cosmological argument and it goes like this

Photons are redshifted, losing energy as space expands that is our observation we see. If we observe a fixed number of photons, the number stays constant while the energy per photon decreases, so the total energy in under observation decreases. Apply that to the whole universe and the universe photons are bleeding energy. So now not even the visible positive side of the universe is not conserving energy using Ethan's approach.

The problem was picked up here and they give the correct answer which is ticked
http://physics.stackexchange.com/questions/13577/photons-in-expanding-space-how-is-energy-conserved

The problem is you can't easily build a single reference frame and Ethan's answer although it seems to comfort him it fails for the same reason. There is no reference frame for what he does and the argument is complete fail but it gives the answer he feels it needs to be. He means well but it is a very glossy media answer to "settle the science" for layman which is unfortunately entirely wrong at it's heart.

The specific problem is Energy conservation only holds on a static background with time-translation invariance. You can't create a reference frame for the universe as a whole so the question is not answerable under normal classic physics and it can not be simplified to a layman level. I don't care how many glossy media articles they put that garbage in and what idiots they drag out to say it, the question can not be answered in that way.

The correct answer is beautifully simplified by Lubos Motl