Don't forget the proton is a composite of quarks. So the mass of the proton is a function of the mass of the quarks and the binding energy. A hack but E=mc^2, so m(proton) = m(quarks) - (binding energy)/c^2. The binding energy changes if the strengths of the forces that bind it change. This means that a change in the electromagnetic force (e.g. changing alpha fine structure constant) or the strong force will change the mass also. Of course, the mass of the electrons or quarks could have changed as well:P
Usually they compare it with other lines in the Hydrogen spectrum. I can't get to the details of the paper, but I suspect that they are comparing the redshift of two different lines and checking that they are the same. If they are different something weird is going on.
It's interesting that they think the ratio effects the strong force. Electrons don't see the strong force, so I'm not sure that this is true - anyone know any better?
The result is accurate to 3.5 sigma - so (possibly) good to about 95 %. Based on a new model of H2 molecule, not sure how well verified it is. I suspect any fool could make any non-standard model measurement fit with string theory so I wouldn't read too much into that.
Well, I think the stars only represent a small amount of baryonic ("normal") matter in a galaxy. So just because stars are randomly distributed, doesn't mean matter is. IIRC the areas where there are stars only have of order a 10% overdensity of baryonic matter compared to the areas where there are no stars.
I think the Dark Matter lobby have a reasonably sound idea. I mean look at it this way:
We have particles that feel the strong, em, weak, gravity forces (quarks). We have particles that feel the em, weak and gravity forces (charged leptons). We have particles that feel the weak and gravity forces (neutrinos). We have particles that feel the gravity force (dark matter).
Seems quite reasonable to me. And we would never see a particle that feels only gravity except through cosmological effects...
If gravity is manifest as a particle, why can't we shield against it?
Gravity is a really really weak force. You would need so much material to shield against it you would drown the effect by the materials own gravity! As everyone else is saying, "neutrinos" - these feel only the weak force (which is much stronger than gravity) and still fly through pretty much anything.
Some waste you want to keep. Uranium will last for about 50-100 years and after that you will want to start using recycling (reprocessing) facilities like Thorpe to use the waste again in fast breeder reactors and the like.
Once that runs out we've invented fusion, right?;-)
This is misleading - naturally occurring uranium is much less radioactive than products from nuclear fission. I would quite happily pick up a fuel rod before it goes into a power plant but I wouldnt go near one once it comes out. The uranium from coal combustion is relatively harmless.
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The point is that if you put uranium into a reactor, some of it undergoes fission into other substances. It turns out that a lot of these substances are very radioactive. OTOH anything radioactive in the earth would have decayed ages ago so naturally occurring stuff is not really very radioactive, relatively speaking anyway.
Okay, so I think the answer is that hadrons do lose more energy going through the atmosphere because of strong force interactions - but some still manage to get through because they have much higher energy to start with. Is that a fair paraphrase?
So I guess I was right about penetrating the lead briefcase or whatever, but perhaps a little dodgy wrt the atmospheric comment...
You can't construct and analyze a particle detector these days without a very good physical model of it.
Okay, I'm half swayed - but two things I don't understand:
1) Where does the energy for all these pions come from? That's 140 MeV per pion... and a pion is a quark anti-quark pair so at least half has to come from the cosmic proton.
2) Why do hadronic calorimeters stop hadronic showers but not muons? Why do hadrons shower whereas muons don't?
Both these points boil down to my previous argument, that protons will have hadronic (i.e. strong force) interactions that the muons won't have, which is the dominant energy loss mechanism. I confess though, I don't have a good reference.
No, the electrons will have pair production and brehmstrahlung. Muons will only have ionisation. See other posts.
Nb: this is a technical subject and not my speciality, but an interesting one - I may be wrong, but I stand by my reference the PDG (linked previously). If you can produce a counter reference, I would be intersted to see it.
Fair point, I was sacrificing accuracy to simplicity. Simplicity is happy but now accuracy rears it's ugly head...
I do stand by my comment that muons of a certain energy penetrate much further through the atmosphere than pions or protons or electrons or gamma at that energy, for the reasons I outlined. Ditto for going through materials like lead. (Except certain special cases like visible light)
Not sure your quite right... From the PDG Handbook*
High-energy electrons predominantly lose energy in matter by bremsstrahlung, and high-energy photons by e+e pair production.
Section 24.7.1
The reason muons don't stop inside our bodies is because they (a) don't interact with atomic nuclei much and (b) are quite heavy.
So there are lots of different particles, like protons and neutrons or electrons, that you could use.
But protons bounce off atomic nuclei because they see something called the "strong force". This means they stop very quickly.
On the other hand, electrons don't see the strong force, which means they don't bounce off the atomic nuclei much at all. In fact, electrons spend all their time bouncing off the electrons that whizz round the outside of the atom.
The thing is though that electrons are much lighter than protons, so even though they only see the electrons in the atom, they still bounce right off them. The same goes with photons (e.g. light, x-rays).
This means that the electrons (and x-rays) get stopped very quickly too.
So both the electrons and protons get stopped very quickly, which means they deposit much more energy inside you = nasty radiation damage!
Muons, OTOH, will zip straight through as they don't see the atomic nuclei and are relatively heavy. This means they do less radiation damage, and you need fewer of them.
This is why you can get away with using atmospheric muons. It also explains why the atmospheric muons are there in the first place - all the other particles get stopped in the atmosphere.*
*Except some special particles called neutrinos - but let's not go there.
Slashdot Mirror
Well you have to go back in time a couple of billion years before it has any effect...
Don't forget the proton is a composite of quarks. So the mass of the proton is a function of the mass of the quarks and the binding energy. A hack but E=mc^2, so m(proton) = m(quarks) - (binding energy)/c^2. The binding energy changes if the strengths of the forces that bind it change. This means that a change in the electromagnetic force (e.g. changing alpha fine structure constant) or the strong force will change the mass also. Of course, the mass of the electrons or quarks could have changed as well :P
Usually they compare it with other lines in the Hydrogen spectrum. I can't get to the details of the paper, but I suspect that they are comparing the redshift of two different lines and checking that they are the same. If they are different something weird is going on.
It's interesting that they think the ratio effects the strong force. Electrons don't see the strong force, so I'm not sure that this is true - anyone know any better?
The result is accurate to 3.5 sigma - so (possibly) good to about 95 %. Based on a new model of H2 molecule, not sure how well verified it is. I suspect any fool could make any non-standard model measurement fit with string theory so I wouldn't read too much into that.
... oh, and the fact that omega is measured by several techniques to be 1 ...
Although having said that, I just found this paper:
8 1.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/9702/97020
which tends to break my argument...
Well, I think the stars only represent a small amount of baryonic ("normal") matter in a galaxy. So just because stars are randomly distributed, doesn't mean matter is. IIRC the areas where there are stars only have of order a 10% overdensity of baryonic matter compared to the areas where there are no stars.
I think the Dark Matter lobby have a reasonably sound idea. I mean look at it this way:
We have particles that feel the strong, em, weak, gravity forces (quarks).
We have particles that feel the em, weak and gravity forces (charged leptons).
We have particles that feel the weak and gravity forces (neutrinos).
We have particles that feel the gravity force (dark matter).
Seems quite reasonable to me. And we would never see a particle that feels only gravity except through cosmological effects...
Gravity is a really really weak force. You would need so much material to shield against it you would drown the effect by the materials own gravity! As everyone else is saying, "neutrinos" - these feel only the weak force (which is much stronger than gravity) and still fly through pretty much anything.
Some waste you want to keep. Uranium will last for about 50-100 years and after that you will want to start using recycling (reprocessing) facilities like Thorpe to use the waste again in fast breeder reactors and the like.
;-)
Once that runs out we've invented fusion, right?
This is misleading - naturally occurring uranium is much less radioactive than products from nuclear fission. I would quite happily pick up a fuel rod before it goes into a power plant but I wouldnt go near one once it comes out. The uranium from coal combustion is relatively harmless.
---
The point is that if you put uranium into a reactor, some of it undergoes fission into other substances. It turns out that a lot of these substances are very radioactive. OTOH anything radioactive in the earth would have decayed ages ago so naturally occurring stuff is not really very radioactive, relatively speaking anyway.
...and by using them in every speech for the next ten years, he serves to make publicity for the terrorists - score 1 to them.
...and when they get LISA up, we'll have even more sensitivity.
Hmm... the top 10 maybe dropouts - the top 100 even. But if you look at the top 1000, 10 000, 100 000?? 1000 000?
Maximise your chances of being successful, rather than of being the richest person in the world.
Besides, money isn't everything.
Had to have been ;-)
No they try to get us to patent it all now so that they can make money out of it.
Okay, so I think the answer is that hadrons do lose more energy going through the atmosphere because of strong force interactions - but some still manage to get through because they have much higher energy to start with. Is that a fair paraphrase?
So I guess I was right about penetrating the lead briefcase or whatever, but perhaps a little dodgy wrt the atmospheric comment...
You can't construct and analyze a particle detector these days without a very good physical model of it.
Don't I know it...
Okay, I'm half swayed - but two things I don't understand:
1) Where does the energy for all these pions come from? That's 140 MeV per pion... and a pion is a quark anti-quark pair so at least half has to come from the cosmic proton.
2) Why do hadronic calorimeters stop hadronic showers but not muons? Why do hadrons shower whereas muons don't?
Both these points boil down to my previous argument, that protons will have hadronic (i.e. strong force) interactions that the muons won't have, which is the dominant energy loss mechanism. I confess though, I don't have a good reference.
No, the electrons will have pair production and brehmstrahlung. Muons will only have ionisation. See other posts.
Nb: this is a technical subject and not my speciality, but an interesting one - I may be wrong, but I stand by my reference the PDG (linked previously). If you can produce a counter reference, I would be intersted to see it.
No... they pair produce in the field of the atomic electrons I think.
Fair point, I was sacrificing accuracy to simplicity. Simplicity is happy but now accuracy rears it's ugly head...
I do stand by my comment that muons of a certain energy penetrate much further through the atmosphere than pions or protons or electrons or gamma at that energy, for the reasons I outlined. Ditto for going through materials like lead. (Except certain special cases like visible light)
Not sure your quite right... From the PDG Handbook* High-energy electrons predominantly lose energy in matter by bremsstrahlung, and high-energy photons by e+e pair production. Section 24.7.1
The reason muons don't stop inside our bodies is because they (a) don't interact with atomic nuclei much and (b) are quite heavy.
So there are lots of different particles, like protons and neutrons or electrons, that you could use.
But protons bounce off atomic nuclei because they see something called the "strong force". This means they stop very quickly.
On the other hand, electrons don't see the strong force, which means they don't bounce off the atomic nuclei much at all. In fact, electrons spend all their time bouncing off the electrons that whizz round the outside of the atom.
The thing is though that electrons are much lighter than protons, so even though they only see the electrons in the atom, they still bounce right off them. The same goes with photons (e.g. light, x-rays).
This means that the electrons (and x-rays) get stopped very quickly too.
So both the electrons and protons get stopped very quickly, which means they deposit much more energy inside you = nasty radiation damage!
Muons, OTOH, will zip straight through as they don't see the atomic nuclei and are relatively heavy. This means they do less radiation damage, and you need fewer of them.
This is why you can get away with using atmospheric muons. It also explains why the atmospheric muons are there in the first place - all the other particles get stopped in the atmosphere.*
*Except some special particles called neutrinos - but let's not go there.
Here's a general particle physics wikipedia