What is constant alpha?

[ccwebb]

I came across two articles in Science News of alpha not being a constant. (I do not have a subscription yet, so I have been unable to read the full article.) First off, what is alpha and why does it matter if it is a constant or not?

 

Yes I have (tired) to read/study about this, even went to Wikipedia, but as a funny comic strip indicated in another thread of mine, it was difficult to keep focused on the topic.

 

 

[Endercreeper01]

Can you provide a link to the article?

[swansont]

Alpha is the fine structure constant, which is an indication of the electromagnetic coupling strength. If it changes, there are implications for formation of molecules and other interactions.

 

I know of two challenges to it being constant based on astronomy measurements, but they are by the same group using the same method. It will gain credence if others can replicate the results. Measurements of the current rate of change are performed with atomic clocks and are consistent with zero with small error bars.

[Schneibster]

The value of alpha or α is 1/137.

 

A good way (though not mathematically precise) is to think of it as the chance, given everything else is just right, i.e. the angles of the electron and photon are just right, and they'll intersect at a given spacetime location with a known uncertainty, that an electron and a photon will actually interact. If they were little balls they'd interact every time, since they're subatomic quantum particles they only interact 1/137 of the time.

 

But as I say it's a notionally, but not numerically, accurate answer. So don't get too stuck on the analogy.

[ccwebb]

There are two articles written by Peter Weiss that deals with the topic of 'Changing Constants'; one was in 2002 and the other in 2006. I found both at the Science News website. (link is in the first post.)

 

Thank you swansont, as always, you kept it to my understanding! The next question is, why would a constant be challenged? Sure, when it is first proposed, but why now? As you indicated, "there are measurements using atomic clocks" and I am sure countless number of scientist have already challenged this idea.

[Schneibster]

Interestingly, it wasn't until SN1987a that we had clear evidence that the speed of light is the same in the Magellanic Clouds as it is here on Earth; we were able to see the explosion sequentially lighting up clouds that had previously been emitted by the star, that were light years away from it. The Clouds are far enough away to let us see this effect clearly over years, but close enough that we can measure the sizes of the cloud structures pretty accurately by trigonometry. As a result we can say that the speed of light hasn't changed measurably in the last 187,000 years (which is how long ago SN1987a exploded; remember, we first saw the light in 1987).

 

And a changing speed of light would be an effect of a changing alpha. Also changing ε₀ and μ₀ can be expected. Stars would burn differently. Chemistry would work differently, because the electron cloulds would interact differently. Likely molecules for us, like CO₂ and CH₄ and H₂O and NH₃ would be rare or nonexistent. Benzene likely would not be possible; depending on the exact change, a four-carbon or eight-carbon ring would be more likely than a six-carbon ring. Organic chemistry would be totally different, and petroleum from the ground would be of a different composition. Algae might not be able to live. "Human beings" as we know them could not exist; they'd be chemically impossible.

 

Alpha is a pretty basic constant.

Edited February 18, 2014 by Schneibster

[swansont]

 

Thank you swansont, as always, you kept it to my understanding! The next question is, why would a constant be challenged? Sure, when it is first proposed, but why now? As you indicated, "there are measurements using atomic clocks" and I am sure countless number of scientist have already challenged this idea.

 

Why challenge it and check it? Because that's what scientists do. Asking "is this really constant" or "what is the range of validity of this concept" are some basic things a physicist would ask. It's a challenge to measure something very small, so new measurements are always pushing some part of an experiment to new levels of precision.

The value of alpha or α is 1/137.

 

A good way (though not mathematically precise) is to think of it as the chance, given everything else is just right, i.e. the angles of the electron and photon are just right, and they'll intersect at a given spacetime location with a known uncertainty, that an electron and a photon will actually interact. If they were little balls they'd interact every time, since they're subatomic quantum particles they only interact 1/137 of the time.

 

But as I say it's a notionally, but not numerically, accurate answer. So don't get too stuck on the analogy.

 

That's not one I've ever heard. There are a bunch of other physical interpretations

http://en.wikipedia.org/wiki/Fine-structure_constant#Physical_interpretations

[Schneibster]

The easiest other one, I suppose, is the ratio of the strengths of the gravity and electric forces of two charged massive point particles at any distance. And a lot of authors describe it that way. (I will not pollute the language with stuff like "massful.")

[Radical Edward]

Why challenge it and check it? Because that's what scientists do. Asking "is this really constant" or "what is the range of validity of this concept" are some basic things a physicist would ask. It's a challenge to measure something very small, so new measurements are always pushing some part of an experiment to new levels of precision.

 

That's not one I've ever heard. There are a bunch of other physical interpretations

http://en.wikipedia.org/wiki/Fine-structure_constant#Physical_interpretations

He's referring to the interpretation put forth by Feynman.

[Schneibster]

Errr, no. Those are interpretations of all of quantum mechanics. Alpha is just one variable.

This bothered me all afternoon so I went and hunted it down.

 

I got it from Susskind 2005, The Cosmic Landscape, page 49, in the section titled "The Fine Structure Constant," which is very promising for this subject.

 

 

 

The operation of a television screen provides a good illustration of such probabilities. The light coming from a TV screen is composed of photons that are created when electrons strike the screen. The electrpons are ejected from an electrode at the rear of the set and are guided to the screen by electric and magnetic fields. But not every electron that hits the screen emits a photon. Some do. Most don't. Roughly speaking the probability that any particular electron will radiate a quantum of light is given by the fine structure constant α. In other words, only one lucky electron out of 137 emits a photon. That is the meaning of α; it is the probability that an electron, as it moves along its trajectory, will capriciously emit a photon.

[imatfaal]

Errr, no. Those are interpretations of all of quantum mechanics. Alpha is just one variable.

...

 

Perhaps read the linked page rather than just the abbreviated url - in full the section linked to is

 

http://en.wikipedia.org/ wiki/ Fine-structure_constant#Physical_interpretations

 

with a few spaces added so that the forum software doesn't abbreviate.

[Schneibster]

I'm totally confused. Feynman doesn't appear until much later in the article: http://en.wikipedia.org/wiki/Fine-structure_constant#Numerological_explanations

 

And that's not an "interpretation."

[swansont]

imatfaal was pointing out that the link listed interpretations of alpha, not QM.

 

Also, I don't know what unspoken context there is for the Susskind example, but what he claimed makes no sense. The electrons possibly emitting photons along their trajectory has nothing to do with the photons the screen emits, and those emissions are by atoms, not electrons. The photons come from electron excitation of the phosphor, and every excitation gives you a photon.

 

Also, an efficiency of 1/137 is almost certainly wrong. TV CRT beams are a few mA of current. Consider a 1 mA current of electrons causing the emission of photons at 100% efficiency, with an energy of ~2 eV. That 2 mW of light, and the maximum brightness is 683 lumens/Watt (at 555 nm). So 1 mA is less than 2 lumens (much less, unless the light is green). With an efficiency of 1/137, that's around 0.01 lumens per mA. For reference, 40W light bulb is ~300 lumens (you'd need to collect all the light for a direct comparison). There seems to be a few orders of magnitude difference here; TV screens are brighter than that. The example doesn't stand up to scrutiny, and doesn't even make sense.

[Schneibster]

Ummm, OK.

 

So this is uncomfortable.

 

How about you write him and tell him and let's see what he says. He being famous prize-winning physicist inventor of string theory and stuff. And you being anonymous internet dude.

 

That's the whole entire paragraph word for word unless I made a typo. There's nothing else in it, and no further explanation of the example before or after it. Susskind isn't a journalist. He's a physicist. This isn't a paper on arXiv. It's a published book.

 

I am having a lot of trouble with a relatively anonymous moderator on a physics forum appearing to call Leonard Susskind a liar. Sorry if that wasn't what you intended but it sure looks that way to me. For that matter, if an anonymous moderator on a physics forum insists Leonard Susskind is "wrong," I'm not going to have a lot of patience with that either.

 

Next you'll be telling me Gravitation is all wrong because Kip Thorne is an idiot.

 

And BTW I'm an EE and know all about how televisions work.

 

Last but not least I know the difference between an interpretation of quantum mechanics and an interpretation of alpha. And I'm trying to be nice because I consider it pretty insulting to be accused of not knowing that.

Edited February 21, 2014 by Schneibster

[hypervalent_iodine]

!

Moderator Note

Schneibster,

 

We generally discourage the use of logical fallacy here. If you disagree with swansont's post, perhaps you could try arguing with facts instead of an appeal to authority?

 

Please do not respond to this mod note within the thread.

[Schneibster]

imatfaal was pointing out that the link listed interpretations of alpha, not QM.

Also, I don't know what unspoken context there is for the Susskind example, but what he claimed makes no sense. The electrons possibly emitting photons along their trajectory has nothing to do with the photons the screen emits, and those emissions are by atoms, not electrons. The photons come from electron excitation of the phosphor, and every excitation gives you a photon.

 

Also, an efficiency of 1/137 is almost certainly wrong. TV CRT beams are a few mA of current. Consider a 1 mA current of electrons causing the emission of photons at 100% efficiency, with an energy of ~2 eV. That 2 mW of light, and the maximum brightness is 683 lumens/Watt (at 555 nm). So 1 mA is less than 2 lumens (much less, unless the light is green). With an efficiency of 1/137, that's around 0.01 lumens per mA. For reference, 40W light bulb is ~300 lumens (you'd need to collect all the light for a direct comparison). There seems to be a few orders of magnitude difference here; TV screens are brighter than that. The example doesn't stand up to scrutiny, and doesn't even make sense.

 

I knew we were discussing alpha. It's in the title of every post.

 

I guess I can only point out that Susskind was making an analogy he hoped lots of people could get.

 

Sounds like you pushed it beyond its limits.

 

Incidentally, http://en.wikipedia.org/wiki/Leonard_Susskind

I also have to say that Susskind's description works well with the conceptual picture of the electric charge of the electron constantly spitting out and reabsorbing virtual photons.

 

And that was the sort of association I made with it. I'm pretty sure that's what he intended to convey.

Here's a paper on the quantum efficiency of CRTs. http://k-ids.or.kr/journal/B/11_3/1126/articlefile/article.pdf

 

It's umaround25%withanamplifiersorry. AndwehaventevendiscussedthequantumefficiencyofcommercialCCDssorryagain.

Edited February 21, 2014 by Schneibster

[Sensei]

I got it from Susskind 2005, The Cosmic Landscape, page 49, in the section titled "The Fine Structure Constant," which is very promising for this subject.

 

 

in mine version of book (translation from English from 2011) pages 33 to 91 are section "World according to Feynman".

[Schneibster]

In the English edition that's the whole First Chapter. The subsection is titled "The Fine Structure Constant" and is after subsection "Antimatter" and before subsection "Quantum Chromodynamics," with another couple subsections afterward; all of these are inside Chapter 1, "The World According to Feynman."

 

I will be interested to know about the translation, actually. Can you find the parts I am referring to? How can I help you?

Edited February 21, 2014 by Schneibster

[Sensei]

Okay, I found it on page 74.

Thanks for pointers.

[Schneibster]

Okay, I found it on page 74.

Thanks for pointers.

 

You bet. Anytime. My pleasure.

[Sensei]

Errr, no. Those are interpretations of all of quantum mechanics. Alpha is just one variable.

This bothered me all afternoon so I went and hunted it down.

 

I got it from Susskind 2005, The Cosmic Landscape, page 49, in the section titled "The Fine Structure Constant," which is very promising for this subject.

 

The operation of a television screen provides a good illustration of such probabilities. The light coming from a TV screen is composed of photons that are created when electrons strike the screen. The electrpons are ejected from an electrode at the rear of the set and are guided to the screen by electric and magnetic fields. But not every electron that hits the screen emits a photon. Some do. Most don't. Roughly speaking the probability that any particular electron will radiate a quantum of light is given by the fine structure constant α. In other words, only one lucky electron out of 137 emits a photon. That is the meaning of α; it is the probability that an electron, as it moves along its trajectory, will capriciously emit a photon.

 

I agree with Swansont's statement from #13 post.

This paragraph of book is almost certainly wrong.

Edited February 22, 2014 by Sensei

[Schneibster]

I think it loses a lot in translation.

[Sensei]

I think it loses a lot in translation.

 

 

It sounds the same either in mine native language and provided by you English version. Nearly literally the same.

Any layman (not to mention scientists) who has Crookes tube (which cost 70 usd on ebay) can conduct experiment at home and show that provided by him values are not correct.

Thickness of material electron strikes and velocity of electron, have more influence on whether photon will be emitted, or electron will pass through it without collision.



When we connect to it 1 A current it means there is 6.25*10^18 electrons emitted per second.
If just 1 per 137 electrons has to emit photon as Susskind said, 6.25*10^18 / 137 = 4.56*10^16 photons emitted.
It's just a matter of measuring intensity of light emitted by wall that's on electron's path.

If you have not seen it at work click here
http://en.wikipedia.org/wiki/Crookes_tube

http://www.youtube.com/watch?v=CsjLYLW_3G0

[Schneibster]

I'm not sure why we're arguing about this. Do you know what a "metaphor" is?

[mooeypoo]

Did you really just resort to moving the goal post now?

You start by saying X is true.

Then insist X is true because Susskind said it (even called it awkward, not sure for whom)

Then claim it probably loses something in translation

And now it's a metaphor.

 

 

I wonder, then, at what point are we going to consider the remote and terribly implausible possibility that there was an error in the invincible text's content or (no!) in your initial assertion.