L. Susskind -- The "Megaverse"

[Perpetual Student]

...
...
I have a dislike for people who want to merely assume that there is a multiverse without providing evidence for a multiverse. Odd that people on this particular board would want to accept a multiverse without such evidence.
...
...

It does not appear obvious to me that anyone on this board assumes or accepts there is a multiverse. Everyone here seems to regard it as speculation -- one whose demonstration is currently far out of reach. Those who find it an interesting (even satisfying) speculation do so because it has a logical connection to the fine-tuning question.
The only dogmatic approach to this discussion seems to have come from you with your mischaracterizations of others (like this):

Let me try again:

1. People claim other universes (of some sort) exist with some specific properties.
2. The reason: fine-tuning.
3. We know that fine-tuning exists because other universes exist...

Susskind presents a well reasoned argument in the brief interview I linked:
In summary:
We see fine-tuning. He gives examples of this, while emphasizing the extraordinarily small value of Λ. He then suggests that the megaverse (his preferred term over multiverse) conjecture would allow for countless variations, one of which would be our known universe.
He uses the analogy of the earth among countless other possible conditions (size, orbit, sun, etc.) for planets. It's that simple. It's a speculative conjecture with some logical support. Take it or leave it.

 

[Perpetual Student]

...
...
Everyone knows that the fine structure constant is a variable by definition but not by name. This is a historical accident because it was defined decades before the formation of QFT and the discovery that it would vary with energy.
...
...

How is this true?

α = e²cμ₀/2h -- among several other expressions (LINK), all consisting of constants. So, how can α vary with energy? Does e vary with energy? How about μ, c or h? These are all constants that do not vary. If you can do so, please explain.

(Farsight: I really have no interest in Duffield-make-believe, so don't bother to respond. This thread is for people who have a genuine interest in physics and cosmology; there is a separate thread discussing crackpots.)

 

[Reality Check]

α = e²cμ₀/2h -- among several other expressions (LINK), all consisting of constants.

Classically α is a constant that is a measure of the strength of the electromagnetic interaction and so does not change.
Then along comes quantum electrodynamics which is a relativistic theory. The electromagnetic interaction now changes with energy so that α becomes the strength of the electromagnetic interaction at zero energy. You can think of it as energy increases, the energy scale of electron mass increases (have a look at renormalization group) and α increases.

Or another way: At low energies electrons look like charged point particles. At energy increases, you start to see the "dressing" of the bare charge of an electron by positrons, electrons and photons. This increases the effective charge of the electron which is the e in the equation.

 

[Loss Leader]

16 posts have been moved to Farsight's dedicated thread. They appeared to have to do with that topic more than this one. Since I am not a physicist, some guesswork was involved. If you believe your post was on topic and was not a response to Farsight's theories, please feel free to contact the moderating team or simply repost the information. Thank you for staying on topic.

- Loss Leader
Moderating Team

Posted By: Loss Leader

 

[Perpetual Student]

Classically α is a constant that is a measure of the strength of the electromagnetic interaction and so does not change.
Then along comes quantum electrodynamics which is a relativistic theory. The electromagnetic interaction now changes with energy so that α becomes the strength of the electromagnetic interaction at zero energy. You can think of it as energy increases, the energy scale of electron mass increases (have a look at renormalization group) and α increases.

Or another way: At low energies electrons look like charged point particles. At energy increases, you start to see the "dressing" of the bare charge of an electron by positrons, electrons and photons. This increases the effective charge of the electron which is the e in the equation.

So, α has a definite unchanging value as "the strength of the electromagnetic interaction at zero energy." α is indeed a constant!

 

[ServiceSoon]

How can you call the universe we live in "fine-tuned" when there are countless others? It would be more appropriately called "probable" universe.

 

[Hellbound]

How can you call the universe we live in "fine-tuned" when there are countless others? It would be more appropriately called "probable" universe.

Well, see, that's a misunderstanding of why it's called the fine-tuning argument. It's called that because of apparent fine-tuning.

A multiverse hypothesis is a counter to the fine-tuned argument. We aren't fine-tuned, we're just the lucky one out of <insert number here> possibilities.

But it's called the fine-tuning problem becaue we're looking for an answer to why the constants are within the narrow values that are apparently needed for complex structures to form.

As you know, the history of science is a history of man discovering that "we aren't that special". THe universe does not revolve around the Earth. The Sun is not the center of the universe. Our galaxy isn't even anything special compared to other galaxies. We aren't that different from animals, just smarter. Etc, etc, etc.

Multiverse hypothesis are just another possible link to this chain.

 

[sol invictus]

How is this true?

α = e²cμ₀/2h -- among several other expressions (LINK), all consisting of constants. So, how can α vary with energy? Does e vary with energy? How about μ, c or h? These are all constants that do not vary. If you can do so, please explain.

(Farsight: I really have no interest in Duffield-make-believe, so don't bother to respond. This thread is for people who have a genuine interest in physics and cosmology; there is a separate thread discussing crackpots.)

Reposting this:

Which piece of alpha varies is a matter of convention. Constants with dimensions can vary or not - it's entirely up to you and the units you choose. It's only variation in dimensionless combinations of constants (like alpha) that means something physically. But e is the most natural choice.

To say that e cannot vary because of conservation of charge is completely wrong. We're not talking about variations in alpha as a function of time (although even if we were, it would still be wrong).

The "running" of alpha in quantum field theory is as a function of energy scale. It occurs primarily because of virtual electron/anti-electron pairs. The vacuum is full of such pairs, and the more energy your probe has, the more of them it encounters. Charges in a solid or a plasma get screened - they attract opposite charges and repel like charges, which means the charge inside a sphere drawn around the charge is smaller than the "bare" value of the charge. The same happens with the vacuum in QFT - that's why alpha increases at high energy.

 

[sol invictus]

So, α has a definite unchanging value as "the strength of the electromagnetic interaction at zero energy." α is indeed a constant!

Well if you define it that way, it obviously doesn't vary (at least not as a function of energy). But it's often more convenient to define it as the strength of the EM interaction at some definite energy. For some constants, you have to define things that way. For example alpha_strong, the coupling constant of the strong interactions, is zero at very high energies and (formally) infinite at very low energies (which really means the theory is non-perturbative and can't be characterized conveniently by that coupling).

 

[Farsight]

...To say that e cannot vary because of conservation of charge is completely wrong....

Even though electric charge is quantized, and "comes in integer multiples of individual small units called the elementary charge, e, approximately equal to 1.602×10^−19 coulombs" and is "a fundamental conserved property of some subatomic particles". But hey, that's OK, you can report my post and get it shipped out on specious crackpot grounds so you don't have to put up with my awkward skepticism backed by robust physics references, and can be free to peddle multiverse woo.

And Perpetual Student is free to peddle the nonsense that "α is indeed a constant!" When it's a running constant. Which means it varies. Which means it isn't constant. But I'm not allowed to point this out.

Bah.

 

[Perpetual Student]

The "running" of alpha in quantum field theory is as a function of energy scale. It occurs primarily because of virtual electron/anti-electron pairs. The vacuum is full of such pairs, and the more energy your probe has, the more of them it encounters. Charges in a solid or a plasma get screened - they attract opposite charges and repel like charges, which means the charge inside a sphere drawn around the charge is smaller than the "bare" value of the charge. The same happens with the vacuum in QFT - that's why alpha increases at high energy.

OK, (reading further into the Wikipedia article) I see that the fine structure constant approaches 1/128 at interaction energies above 80 GeV compared to its zero energy value of about 1/137. So then, why is α = f(E)e²cμ₀/2h not used as a (more general) expression for α in the various sources I have seen? Is it that f(E) is not known?

 

[Perpetual Student]

...
...

And Perpetual Student is free to peddle the nonsense that "α is indeed a constant!" When it's a running constant. Which means it varies. Which means it isn't constant. But I'm not allowed to point this out.

Bah.

By the way, Mr. Duffield, I would say that the magnitude of variation described above for α very much leaves the fine-tuning question unanswered, in spite of your hysterical claims to the contrary. Do you have any logical response, other than your usual hand wave: it's not constant therefore there is no fine-tuning! Try to explain; you have been asked to do so innumerable times.

 

[Reality Check]

...
And Perpetual Student is free to peddle the nonsense that "α is indeed a constant!" When it's a running constant. Which means it varies. Which means it isn't constant. But I'm not allowed to point this out.
Bah.

Oh dear - the cardinal sin of cranks: quote mining, Farsight .

This is what Perpetual Student wrote:

So, α has a definite unchanging value as "the strength of the electromagnetic interaction at zero energy." α is indeed a constant!

(my emphasis added)
Perpetual Student is learning why α is not a constant.

You are allowed to point out the obvious physics fact that everyone in this thread knows (now if not before) - the fine-structure constant despite its name is not a constant and varies with energy.

You should not constantly repeat what everyone in this thread knows as if we could not understand what people have posted here, i.e. the explanation that fine-structure constant varies with energy and why.

You should not constantly repeat that fine-structure constant varies with energy as if this something to do with the thread topic.
ETA: If you have some evidence that the observed variation of α with energy (or the speculated variation with location or time) cannot happen in other universes then you need to present it .

 

[sol invictus]

OK, (reading further into the Wikipedia article) I see that the fine structure constant approaches 1/128 at interaction energies above 80 GeV compared to its zero energy value of about 1/137. So then, why is α = f(E)e²cμ₀/2h not used as a (more general) expression for α in the various sources I have seen? Is it that f(E) is not known?

Actually alpha(E) is known quite precisely. I guess you're asking why people don't bother to make explicit that alpha (or e) depends on energy? I suppose it's because it's not very important for anything except precision particle physics, and everyone in that field knows about running constants.

 

[Perpetual Student]

del.

 

[Perpetual Student]

Actually alpha(E) is known quite precisely. I guess you're asking why people don't bother to make explicit that alpha (or e) depends on energy? I suppose it's because it's not very important for anything except precision particle physics, and everyone in that field knows about running constants.

That's exactly what I was asking. I find it peculiar that α(Ε) is nowhere to be seen in the Wikipedia article. Under the section called "Is the fine-structure constant actually constant?" the article discusses time and space variations in α, while only mentioning in passing that it "is known to approach 1/128 at interaction energies above 80 GeV"

Upon further investigation, I have learned that it becomes quite a complex problem, since at the electroweak scale (E>2.5X10¹¹eV), the weak force gets as strong as electromagnetism and physics is expressed in terms of the fine-structure constants for the SU(2) and U(1) electroweak gauge groups.
Good Grief -- there is so much complexity to this stuff!

 

[Farsight]

By the way, Mr. Duffield, I would say that the magnitude of variation described above for α very much leaves the fine-tuning question unanswered, in spite of your hysterical claims to the contrary. Do you have any logical response, other than your usual hand wave: it's not constant therefore there is no fine-tuning! Try to explain; you have been asked to do so innumerable times.

I've explained this lots of times. Let's see if you'll take it on board this time. See the fine-tuned universe on wiki:

"The fine-tuned Universe is the proposition that the conditions that allow life in the Universe can only occur when certain universal fundamental physical constants lie within a very narrow range".

Follow the link to fundamental physical constants and you can read this:

"In physics, a dimensionless physical constant (sometimes fundamental physical constant) is a universal physical constant that is dimensionless – having no unit attached, so its numerical value is the same under all possible systems of units. The best known example is the fine structure constant α, with the approximate value 1/137.036.

However, the term fundamental physical constant has also been used (as by NIST) to refer to universal but dimensional physical constants such as the speed of light c, vacuum permittivity ε0, Planck's constant h, or the gravitational constant G".

You know that alpha isn't a constant. You know about conservation of charge. You know that the coordinate speed of light varies in a gravitational field, and you know that there are VSL papers on arXiv. You know that some people think Planck's constant might vary. You know about the Dirac Large Numbers hypothesis where G is said to vary over time. You know about the cosmological constant wherein Λ is "equivalent to an energy density in otherwise empty space", and you know about conservation of energy and the expanding universe which surely tells you that Λ varies over time. So you know enough to be skeptical of "fine tuned constants" used to justify the Goldilocks multiverse. You know enough to smell woo. Don't you?

No. Like some happy clappy creationist you cling to your woo and dismiss everything I say and all the references I provide. And then you peddle it on JREF, and you even say "α is indeed a constant!"

Bah.

 

[Perpetual Student]

I've explained this lots of times. Let's see if you'll take it on board this time. See the fine-tuned universe on wiki:

"The fine-tuned Universe is the proposition that the conditions that allow life in the Universe can only occur when certain universal fundamental physical constants lie within a very narrow range".

Follow the link to fundamental physical constants and you can read this:

"In physics, a dimensionless physical constant (sometimes fundamental physical constant) is a universal physical constant that is dimensionless – having no unit attached, so its numerical value is the same under all possible systems of units. The best known example is the fine structure constant α, with the approximate value 1/137.036.

However, the term fundamental physical constant has also been used (as by NIST) to refer to universal but dimensional physical constants such as the speed of light c, vacuum permittivity ε0, Planck's constant h, or the gravitational constant G".

You know that alpha isn't a constant. You know about conservation of charge. You know that the coordinate speed of light varies in a gravitational field, and you know that there are VSL papers on arXiv. You know that some people think Planck's constant might vary. You know about the Dirac Large Numbers hypothesis where G is said to vary over time. You know about the cosmological constant wherein Λ is "equivalent to an energy density in otherwise empty space", and you know about conservation of energy and the expanding universe which surely tells you that Λ varies over time. So you know enough to be skeptical of "fine tuned constants" used to justify the Goldilocks multiverse. You know enough to smell woo. Don't you?

No. Like some happy clappy creationist you cling to your woo and dismiss everything I say and all the references I provide. And then you peddle it on JREF, and you even say "α is indeed a constant!"

Bah.

I'm not certain what to make of that response. On the one hand, I am astonished that you believe you have actually produced a meaningful argument. On the other hand, it seems to be just another one of your hand-waving bluffs -- so no surprise there.

Bah, indeed! What a waste of time -- dealing with Duffield-fantasy physics.

 

[Reality Check]

What does the variation of the alpha with energy have to do with megaverses

I've explained this lots of times.

Sorry, Farsight, but merely repeating what every one already knows is not an explanation - it is just boring and repetitive !
We know

1. that alpha isn't a constant.
2. about the conservation of charge.
3. that coordinate speed of light varies in a gravitational field and that by definition the actual speed of light does not vary.
4. VSL theories exist, are speculative (to put it charitably) and that there are VSL papers on arXiv.
5. that there are people who think that Planck's constant might vary.
6. about the Dirac Large Numbers hypothesis.
7. that the cosmological constant wherein Λ is "equivalent to an energy density in otherwise empty space" and that energy density does not vary with time.
8. about the conservation of energy and the expanding universe.
9. that this does not tell us that Λ varies over time (unless we remain ignorant like you, Farsight, of the energy density caused by Λ )

What we do not know and you have not explained is what these items have to do with this thread.
So I will start with a simple question about the items:

Farsight,

1. What does the observed variation of the fine-structure constant with energy tell us about the existence or not of the multi-universe?
2. Ditto for conservation of charge?
3. Ditto for coordinate speed of light varying in a gravitational field.
4. Ditto for the existence of VSL theories.
5. Ditto for Planck's constant might vary.
6. Ditto for Dirac Large Numbers hypothesis.
7. Ditto for the fact that Λ has a constant energy density.
8. Ditto for conservation of energy and the expanding universe.
9. Ditto (again!) for the fact that Λ has a constant energy density.

ETA: Alternately, Explain how the "fine-tuning" of the variation of the fine-structure constant with energy means that the variation of the fine-structure constant with energy is not fine-tuned !
First asked 23 July 2013 - 0 days and counting, Farsight .

 

[Farsight]

I've already answered it. See above:

"The fine-tuned Universe is the proposition that the conditions that allow life in the Universe can only occur when certain universal fundamental physical constants lie within a very narrow range".

Only they aren't constant, and they don't lie within a very narrow range, so that's the end of that. Bye-bye Goldilocks multiverse. Bye-bye woo.