Is alpha a constant (split from cosmological constant)

[immortal]

Yeah even I heard that. The fine structure constant is changing i.e. alpha = e*2/hc. If this constant is changing than one of the other constant should change. The value of alpha is 1/137. But there is no abrupt change and its just 1% true and 99% fluke. I think it is the speed of light which is changing. I don't know much about cosmos.

[swansont]

Yeah even I heard that. The fine structure constant is changing i.e. alpha = e*2/hc. If this constant is changing than one of the other constant should change. The value of alpha is 1/137. But there is no abrupt change and its just 1% true and 99% fluke. I think it is the speed of light which is changing. I don't know much about cosmos.

 

There are many measurements that show that the fine structure constant is currently not changing and has not changed over a significant amount of time. There are a few unconfirmed ones where it might have had a slightly different value in the distant past, of which I am aware. To what experiment(s) are you referring?

[immortal]

There are many measurements that show that the fine structure constant is currently not changing and has not changed over a significant amount of time. There are a few unconfirmed ones where it might have had a slightly different value in the distant past, of which I am aware. To what experiment(s) are you referring?

 

Actuall I read it on webster world.

 

Here are some links:-

http://www.physorg.com/news3665.html

http://www.ast.cam.ac.uk/~mim/res.html

http://moriond.in2p3.fr/EW/2003/Transparencies/2_Monday/2_2_afternoon/2_2_6_Murphy/M_Murphy.pdf

[swansont]

AFAIK Murphy's work has not yet been replicated.

[immortal]

It is just a matter of time where a group of scientists confirms it.

 

Links:

http://physicsweb.org/articles/news/11/3/18/

[swansont]

It is just a matter of time where a group of scientists confirms it.

 

Links:

http://physicsweb.org/articles/news/11/3/18/

 

Or disproves it, like a bunch of other measurements that have been made. Let's not get ahead of the actual state of affairs.

 

"The method, which has yet to be verified using astronomical observations, involves measuring how hydrogen atoms absorbed photons from the cosmic microwave background."

 

IOW, they discuss a method, not results.

[lucaspa]

It is just a matter of time where a group of scientists confirms it.

 

Links:

http://physicsweb.org/articles/news/11/3/18/

 

This is where patience needs to be exercised. I note from the original websites that even Murphy is being cautious about the changing constant: "Murphy is careful not to claim that the case is closed, and he says that nobody can really say that alpha varies until another type of experiment has confirmed it."

 

You don't have "another type of experiment" yet. All 3 of your original websites are different sources to the same (and single) study.

 

Also, the change is not very large:

 

" By comparing these fingerprints with those obtained in experiments on Earth, he concludes that alpha has changed by about one part in two-hundred-thousand during the last 10 billion years. "

 

My "not very large" is an understatement. BTW, both quotes are from http://www.physorg.com/news3665.html

 

Just be patient and let the physicists fight it out. If Murphy et al.'s work is sound, there will be other studies. In the meantime, I would advise you not be an advocate of preliminary data that is not your own.

[swansont]

The main problem is that measuring zero is usually really hard to do. All you need is a tiny systematic error and you're done for. And if you are trying to exclude zero, you have similar issues.

[ajb]

Zero is not very natural in physics. If the constant is set to zero classically, then quantum effects are likely to push this from zero. This is generally a fine-tuning problem. That is you would have to set your classical value very precisely to get the observed value of zero. Unless you have a symmetry or some other mechanism to stop this happening.

 

So I think that an exact value of zero would be very hard to explain, but a small non-zero value would be much more natural. So as swansont has pointed out, trying to see if it is zero or just very small is hard to do.

[lucaspa]

The main problem is that measuring zero is usually really hard to do. All you need is a tiny systematic error and you're done for. And if you are trying to exclude zero, you have similar issues.

 

ajb and swansont: we have two different constants being discussed. The OP was the cosmological constant or lambda. Immortal is talking about the fine structure, or alpha, constant. Alpha is NOT zero.

 

Murphy eat all are claiming that their measurements of alpha exclude systematic errors that other people introduced because they did not use the internal checks Murphy et al. incorporated:

 

"Other researchers have published results which suggest that alpha does not change. However Dr Murphy's work is the most detailed survey ever performed. He says that the internal checks in his method, which other research groups did not use, make this the most reliable measurement to date. "

 

Ajb, lambda was originally introduced in the relativity equations by Einstein because gravity would collapse the universe. So lambda was originally arbitrarily set to a positive value that would counter gravity and keep the universe static. When it was found that the universe was expanding, lamba was no longer needed and was arbitrarily set to zero; it was never measured. The expansion was accounted for by the impetus from the Big Bang. The experiments looking at supernovae showed that the expansion of the universe was accelerating. The only part of the Einstein equations that could be used to account for this was lambda, which now had to be positive again to push the universe to expand.

[swansont]

ajb and swansont: we have two different constants being discussed. The OP was the cosmological constant or lambda. Immortal is talking about the fine structure, or alpha, constant. Alpha is NOT zero.

I don't think anyone here has contended that alpha is zero

 

What we were challenging/discussing, because of immortal's post, is actually the change in alpha, and what is under contention is whether that is a constant. i.e. if [math]\Delta\alpha = 0[/math]

 

I'll split this off to avoid further confusion

[ajb]

Ajb, lambda was originally introduced in the relativity equations by Einstein because gravity would collapse the universe. So lambda was originally arbitrarily set to a positive value that would counter gravity and keep the universe static. When it was found that the universe was expanding, lamba was no longer needed and was arbitrarily set to zero; it was never measured.

 

I am well aware of the classical origin of the cosmological constant.

 

 

From a modern point of view, you should include all terms possible in a classical Lagrangian that are consistent with the symmetries you want and quantum field theory, (we ignore remormalisation of general relativity for now). Thus, one should include the cosmological constant (and topological terms) and explain why they are zero, if indeed they are. Just setting things to zero by hand is not natural. Indeed as I said, quantum effects may push these values from zero anyway.

 

Maybe more familiar is the [math] F \wedge F[/math] term in Yang Mills theory. Even if you set this topological term to zero classically, instantons will generate this term in the quantum action. So, by analogy one would expect a non-zero cosmological constant.

[Meir Achuz]

http://arxiv.org/abs/0705.3704

[Severian]

Well alpha definitely does change with time to some extent. Its value is dependent on energy, so when the universe was very hot, it would have a different value. I presume this is taken into account for the dark energy measurements(?).

[Meir Achuz]

Well alpha definitely does change with time to some extent. Its value is dependent on energy, so when the universe was very hot, it would have a different value. I presume this is taken into account for the dark energy measurements(?).

The dependence of alpha on 4-momentum transfer Q^2 does not change the meaning of alpha(Q^2=0) being constant.