Freethought & Rationalism Archive

lpetrich · 04-29-2002, 10:47 PM

I've thought a bit about that, and I consider that argument partially bogus. However, there is a related problem that is more serious, as I shall explain.

One version of the argument states that if some physical constants were only a tiny bit different, then life would be impossible because of such things as chemical bonding and reactions not working properly.

However, if one takes a closer look at the physics behind chemical bonding, it turns out to be less fine-tuned than some people seem to think. This comes from work in quantum chemistry, attempts to predict the properties of chemical bonds using from-scratch quantum mechanics. The only physics that enters is that electrons are spin-1/2, electrostatically interacting, and much lighter than nuclei -- meaning that chemical bonds would keep their angles, relative lengths, and relative energies if the Fine Structure Constant ((electric charge)^2/(4*pi); dimensionless in hbar = c = 1 units) got changed or the electron got lighter or heavier relative to the nuclei.

There are interesting effects in other areas. If the FSC was smaller, then nuclei could extend up to higher masses, since protons would repel each other less. Likewise, if the FSC was larger, then nuclei would extend up to lower masses than they do, because of protons' greater repulsion of each other.

However, there would still be long-lived radioisotopes at the upper end of the mass scale, like the uranium and thorium in our Universe, because instability due to proton repulsion is not a sharp cliff. And stellar-nucleosynthesis processes that produce heavy elements would produce them all the way up to where they become too unstable to last.

It may be possible to derive nuclear binding energies directly from quarks, gluons, and Quantum Chromodynamics in the way that one would do quantum chemistry; one nuclear physicist once joked that particle physicists have turned them into chemists.

But there is a serious difficulty. The electromagnetic FSC has a value of 1/137, making it easy to expand in powers of it, while the QCD equivalent has a value near 1 at the energy scales typical of nucleons -- making it much more difficult. To do nucleon structure requires an enormous amount of computer time, and that's with picturing space-time as a very coarse grid, something like 10*10*10*10. And that barely covers nucleon-nucleon interactions. However, one may be able to hand-wave one's way through nuclear structure by using the fact that the up and down quarks (those in nucleons) are nearly massless (a few MeV) compared to QCD's built-in energy scale of a few hundred MeV.

There are other interesting problems, such as the maximum sizes of planets and the luminosities and lifetimes of stars that can be treated in this way, but I'll skip on that.

There are some features that seem very convenient for us, but it is always possible that there are even better possibilities than those of our Universe.

One curious oddity is that neutrons are more massive than protons. From this, one infers that down quarks are more massive than up ones, which is contrary to the trend shown by their heavier relatives (strange less than charm, bottom less than top). This circumstance has allowed hydrogen to form in the Big Bang; if protons were the unstable one, then the Big Bang would have formed a surfeit of neutrons instead of protons, meaning that hydrogen would be a rare element. Stars would behave differently, since they'd be mostly helium and heavier elements, meaning that they'd burn out more quickly than the stars of our Universe do.

It is interesting that QCD becomes superstrong at energies of a few hundred MeV; this is why nucleons are much more massive than electrons -- the strong quark-gluon and gluon-gluon interactions make the quarks relativistic, with kinetic energies at the QCD energy scale.

If QCD got strong at much less energy, then the rest masses of the up and down quarks would dominate the nucleons' masses, making them not much more massive than electrons. This would have fun consequences in chemical bonds, but I don't think that that would be fatal. There is also the question of nuclei forming with a weak QCD interaction; at energies higher than its natural energy scale, its FSC equivalent gets smaller and smaller in reciprocal-of-logarithm-of-energy fashion.

But if QCD got superstrong at much higher energy scales, then the Universe would still be much like our Universe, but with much more massive nucleons.

Now to the question of weak interactions. These are weak because of a "symmetry breaking" of a combined electromagnetic-weak force that happens at energies of a few hundred GeV. If this symmetry breaking did not happen, then beta decays would happen much faster, and there would be an "extra" electromagnetic-like force. But it happens, and it is likely connected to the masses of the electrons (e, mu, tau) and the quarks. The top quark has a mass of 150 GeV, which is almost the right size, but the other quarks and all the electrons are much less massive, with the "true" electron being 300,000 times less massive! This may be due to some quantum-mechanical spillover, but the details are unclear.

Also, if supersymmetry is real, it is expected to be broken, and the energy scale of this breaking is expected to be a little above the electroweak-interaction symmetry breaking -- and may be related to that breaking.

What makes this symmetry breaking happen is obscure, however; but one thing less obscure is that the FSC equivalents of the electroweak and QCD forces change reciprocal-logarithmically with interaction energy, converging on a single value at about 10^15 GeV -- implying that they were parts of a single interaction that was split up by symmetry breaking. This is, of course, GUT territory. But it's not clear why there is a 10^12 ratio of energies between GUT symmetry breaking and SUSY/electroweak symmetry breaking. It may be connected with the logarithmic rate of change of various interaction constants with energy (huge difference in energy to produce a significant change).

But the GUT energy scale is close to the Planck energy scale of 10^19 GeV (10^19 that of a nucleon, 10^22 that of an electron), that of quantum gravity. This suggests some connection, though exactly what connection is obscure.

But one interesting consequence of this great difference in energies between the familiar elementary-particle world and gravity is that we can live in a very complicated Universe, owing to the resulting weakness of gravity. For example, this enables the largest planet (approx. Jupiter) to have an enormous number of elementary particles, while if the familiar elementary particles had GUT-scale masses, then such an object could not have many particles in it.

However, there does not seem to be much fine tuning here; the gravity-elementary-particle energy-scale discrepancy can be somewhat larger or smaller without producing a drastically-different Universe.

But the final question is: why the particular GUT that had led to the particles of our Universe? What other possibilities could there be?

One attempt to answer this question has been to explore superstring theory, but although that has no free parameters, it does have a large number of possible ground states -- which correspond to different GUT's. What makes a superstring "choose" one and not another is, however, an unsolved problem. Another oddity that must be explained is that superstrings prefer to live in 10 space-time dimensions, while we directly observe only 4. It is expected that the other 6 will curl up into a tiny ball somewhere from Planck-sized to GUT-sized. But why this 4+6 split? Why not some other?

Actually, 4 space-time dimensions are convenient for us, since that allows for complicated structures while allowing objects to orbit each other, producing many of the structures of our familiar Universe. The inverse-square law of gravity and electromagnetism becomes inverse-(D-1) for D space dimensions; if D = 4, then orbits are borderline unstable, and if D is greater than 4, then orbits are definitely unstable. Thus, our familiar Universe has to have 3 space dimensions to allow us to exist.

But superstrings offer an intriguing hypothesis; our Universe could be a supercooled bubble in some "superstring soup" that has several other such bubbles in different ground states, producing Universes that were usually sterile -- and sometimes inhabited when they could allow inhabitants to come into existence, as ours does.

Oolon Colluphid · 04-30-2002, 01:29 AM

Wonderful post! <img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" />

I only wish I understood it...

Just a thought, but would this not be better in Science & Skepticism, or there as well as here? I'll not transfer it cos I can see its anti-creationism point, but S&S folks should see something this good too, yeah?

Cheers, Oolon

Vorkosigan · 04-30-2002, 01:32 AM

OC, don't you think a copy might be made in EoG as well? Lots' of fine tuning arguments there.

Vorkosigan

lpetrich · 04-30-2002, 02:09 AM

As per your suggestions, I've posted copies in EoG and S&S.

Here's a summary:

Some have implied that if certain fundamental constants were only slightly different, the Universe could not allow us to exist, as it were. However, the Universe can have some variations in certain constant values and still remain easily habitable. This is rather easy to work out with chemical bonds and gravity, and somewhat less so with nuclei.

However, the Universe nevertheless contains several "convenience features":

Neutrons being more massive than protons; lots of hydrogen can form in the Big Bang.
Nucleons having much higher masses than their constituent quarks; a side effect is that nuclei can easily form.
Most elementary particles having masses much less than the quantum-gravity energy scale; gravity's resulting weakness allows macroscopic objects to easily exist.
Space-time is 3+1 dimensions, with 3 allowing lots of complexity and stable orbits.

I mention one possibility: a natural selection of Universes, in which bubbles in a superstring soup fall into different ground states, with some of them being habitable Universes like ours..

[ April 30, 2002: Message edited by: lpetrich ]

HRG · 04-30-2002, 02:19 AM

<img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" /> for an excellent post.

Yeah,�wouldn't it be fun if we just had to calculate second- (or at most fourth-) order terms in QCD, as we do in QED ?

One further argument for the dimensionality of space (which goes back to pre-quantum times): in even-dimensional spaces, the fundamental solution to the wave equation *)is not concentrated on the light cone. Thus everything we see or hear would be accompanied by an (visual or acustic) echo, like the afterburn on a cheap TV screen. This would make vision, hearing and communication pretty difficult.

Only in odd-dimensional spaces is a flash seen as a flash, too.

Regards,
HRG.

*) which can be imagined as the light or sound emitted from a very strong and very small source, which is active only for a very small period. Then let all "very"'s go to infinity ....

wdog · 04-30-2002, 12:54 PM

Very nice Ip,

I don't understand it all, for right this minute i am going to reserve the right to ask questions later.

lpetrich · 04-30-2002, 07:03 PM

Quote:

Originally posted by HRG:
 ...
Yeah,�wouldn't it be fun if we just had to calculate second- (or at most fourth-) order terms in QCD, as we do in QED ?

I agree. And in fact, in our Universe, at high-enough energy scales, or more precisely, momentum transfers, one can indeed do that. But that's for energy scales of at least a few GeV.

But it would certainly be an interesting Universe if the QCD FSC was 0.3 or less at nucleon internal momentum transfers. Using an up/down quark mass of 3 MeV, this means a momentum transfer of 1 MeV/c, meaning a size of 10^-12 m or 0.01 Bohr radii, about 1000 times larger than they are in our Universe. The mass would be 10 MeV in this scenario, about 20 electron masses (our Universe: 2000 electron masses).

One interesting question is, when in nuclei, whether such nucleons would simply dissolve into each other rather than retain separate identities, forming a "quark-gluon plasma".

Quote:

HRG:
 ...
One further argument for the dimensionality of space (which goes back to pre-quantum times): in even-dimensional spaces, the fundamental solution to the wave equation *)is not concentrated on the light cone. Thus everything we see or hear would be accompanied by an (visual or acustic) echo, like the afterburn on a cheap TV screen. This would make vision, hearing and communication pretty difficult.
....

Interesting. I remember once working out the propagators, as they are called, for different space dimensions.

Another interesting conundrum is why the Universe's space-time is 3+1 instead of 4+0 or 2+2.

04-29-2002, 10:47 PM	#1
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Fine Tuning? I've thought a bit about that, and I consider that argument partially bogus. However, there is a related problem that is more serious, as I shall explain. One version of the argument states that if some physical constants were only a tiny bit different, then life would be impossible because of such things as chemical bonding and reactions not working properly. However, if one takes a closer look at the physics behind chemical bonding, it turns out to be less fine-tuned than some people seem to think. This comes from work in quantum chemistry, attempts to predict the properties of chemical bonds using from-scratch quantum mechanics. The only physics that enters is that electrons are spin-1/2, electrostatically interacting, and much lighter than nuclei -- meaning that chemical bonds would keep their angles, relative lengths, and relative energies if the Fine Structure Constant ((electric charge)^2/(4pi); dimensionless in hbar = c = 1 units) got changed or the electron got lighter or heavier relative to the nuclei. There are interesting effects in other areas. If the FSC was smaller, then nuclei could extend up to higher masses, since protons would repel each other less. Likewise, if the FSC was larger, then nuclei would extend up to lower masses than they do, because of protons' greater repulsion of each other. However, there would still be long-lived radioisotopes at the upper end of the mass scale, like the uranium and thorium in our Universe, because instability due to proton repulsion is not a sharp cliff. And stellar-nucleosynthesis processes that produce heavy elements would produce them all the way up to where they become too unstable to last. It may be possible to derive nuclear binding energies directly from quarks, gluons, and Quantum Chromodynamics in the way that one would do quantum chemistry; one nuclear physicist once joked that particle physicists have turned them into chemists. But there is a serious difficulty. The electromagnetic FSC has a value of 1/137, making it easy to expand in powers of it, while the QCD equivalent has a value near 1 at the energy scales typical of nucleons -- making it much more difficult. To do nucleon structure requires an enormous amount of computer time, and that's with picturing space-time as a very coarse grid, something like 10101010. And that barely covers nucleon-nucleon interactions. However, one may be able to hand-wave one's way through nuclear structure by using the fact that the up and down quarks (those in nucleons) are nearly massless (a few MeV) compared to QCD's built-in energy scale of a few hundred MeV. There are other interesting problems, such as the maximum sizes of planets and the luminosities and lifetimes of stars that can be treated in this way, but I'll skip on that. There are some features that seem very convenient for us, but it is always possible that there are even better possibilities than those of our Universe. One curious oddity is that neutrons are more massive than protons. From this, one infers that down quarks are more massive than up ones, which is contrary to the trend shown by their heavier relatives (strange less than charm, bottom less than top). This circumstance has allowed hydrogen to form in the Big Bang; if protons were the unstable one, then the Big Bang would have formed a surfeit of neutrons instead of protons, meaning that hydrogen would be a rare element. Stars would behave differently, since they'd be mostly helium and heavier elements, meaning that they'd burn out more quickly than the stars of our Universe do. It is interesting that QCD becomes superstrong at energies of a few hundred MeV; this is why nucleons are much more massive than electrons -- the strong quark-gluon and gluon-gluon interactions make the quarks relativistic, with kinetic energies at the QCD energy scale. If QCD got strong at much less energy, then the rest masses of the up and down quarks would dominate the nucleons' masses, making them not much more massive than electrons. This would have fun consequences in chemical bonds, but I don't think that that would be fatal. There is also the question of nuclei forming with a weak QCD interaction; at energies higher than its natural energy scale, its FSC equivalent gets smaller and smaller in reciprocal-of-logarithm-of-energy fashion. But if QCD got superstrong at much higher energy scales, then the Universe would still be much like our Universe, but with much more massive nucleons. Now to the question of weak interactions. These are weak because of a "symmetry breaking" of a combined electromagnetic-weak force that happens at energies of a few hundred GeV. If this symmetry breaking did not happen, then beta decays would happen much faster, and there would be an "extra" electromagnetic-like force. But it happens, and it is likely connected to the masses of the electrons (e, mu, tau) and the quarks. The top quark has a mass of 150 GeV, which is almost the right size, but the other quarks and all the electrons are much less massive, with the "true" electron being 300,000 times less massive! This may be due to some quantum-mechanical spillover, but the details are unclear. Also, if supersymmetry is real, it is expected to be broken, and the energy scale of this breaking is expected to be a little above the electroweak-interaction symmetry breaking -- and may be related to that breaking. What makes this symmetry breaking happen is obscure, however; but one thing less obscure is that the FSC equivalents of the electroweak and QCD forces change reciprocal-logarithmically with interaction energy, converging on a single value at about 10^15 GeV -- implying that they were parts of a single interaction that was split up by symmetry breaking. This is, of course, GUT territory. But it's not clear why there is a 10^12 ratio of energies between GUT symmetry breaking and SUSY/electroweak symmetry breaking. It may be connected with the logarithmic rate of change of various interaction constants with energy (huge difference in energy to produce a significant change). But the GUT energy scale is close to the Planck energy scale of 10^19 GeV (10^19 that of a nucleon, 10^22 that of an electron), that of quantum gravity. This suggests some connection, though exactly what connection is obscure. But one interesting consequence of this great difference in energies between the familiar elementary-particle world and gravity is that we can live in a very complicated Universe, owing to the resulting weakness of gravity. For example, this enables the largest planet (approx. Jupiter) to have an enormous number of elementary particles, while if the familiar elementary particles had GUT-scale masses, then such an object could not have many particles in it. However, there does not seem to be much fine tuning here; the gravity-elementary-particle energy-scale discrepancy can be somewhat larger or smaller without producing a drastically-different Universe. But the final question is: why the particular GUT that had led to the particles of our Universe? What other possibilities could there be? One attempt to answer this question has been to explore superstring theory, but although that has no free parameters, it does have a large number of possible ground states -- which correspond to different GUT's. What makes a superstring "choose" one and not another is, however, an unsolved problem. Another oddity that must be explained is that superstrings prefer to live in 10 space-time dimensions, while we directly observe only 4. It is expected that the other 6 will curl up into a tiny ball somewhere from Planck-sized to GUT-sized. But why this 4+6 split? Why not some other? Actually, 4 space-time dimensions are convenient for us, since that allows for complicated structures while allowing objects to orbit each other, producing many of the structures of our familiar Universe. The inverse-square law of gravity and electromagnetism becomes inverse-(D-1) for D space dimensions; if D = 4, then orbits are borderline unstable, and if D is greater than 4, then orbits are definitely unstable. Thus, our familiar Universe has to have 3 space dimensions to allow us to exist. But superstrings offer an intriguing hypothesis; our Universe could be a supercooled bubble in some "superstring soup" that has several other such bubbles in different ground states, producing Universes that were usually sterile -- and sometimes inhabited when they could allow inhabitants to come into existence, as ours does.

04-30-2002, 02:09 AM	#4
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	As per your suggestions, I've posted copies in EoG and S&S. Here's a summary: Some have implied that if certain fundamental constants were only slightly different, the Universe could not allow us to exist, as it were. However, the Universe can have some variations in certain constant values and still remain easily habitable. This is rather easy to work out with chemical bonds and gravity, and somewhat less so with nuclei. However, the Universe nevertheless contains several "convenience features": Neutrons being more massive than protons; lots of hydrogen can form in the Big Bang. Nucleons having much higher masses than their constituent quarks; a side effect is that nuclei can easily form. Most elementary particles having masses much less than the quantum-gravity energy scale; gravity's resulting weakness allows macroscopic objects to easily exist. Space-time is 3+1 dimensions, with 3 allowing lots of complexity and stable orbits. I mention one possibility: a natural selection of Universes, in which bubbles in a superstring soup fall into different ground states, with some of them being habitable Universes like ours.. [ April 30, 2002: Message edited by: lpetrich ]</p>

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search

04-30-2002, 01:29 AM	#2
Oolon Colluphid Contributor Join Date: Sep 2000 Location: Alibi: ego ipse hinc extermino Posts: 12,591	Wonderful post! <img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" /> I only wish I understood it... Just a thought, but would this not be better in Science & Skepticism, or there as well as here? I'll not transfer it cos I can see its anti-creationism point, but S&S folks should see something this good too, yeah? Cheers, Oolon

04-30-2002, 01:32 AM	#3
Vorkosigan Contributor Join Date: Jan 2001 Location: Barrayar Posts: 11,866	OC, don't you think a copy might be made in EoG as well? Lots' of fine tuning arguments there. Vorkosigan

04-30-2002, 02:19 AM	#5
HRG Veteran Member Join Date: May 2001 Location: Vienna, Austria Posts: 2,406	<img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" /> for an excellent post. Yeah,�wouldn't it be fun if we just had to calculate second- (or at most fourth-) order terms in QCD, as we do in QED ? One further argument for the dimensionality of space (which goes back to pre-quantum times): in even-dimensional spaces, the fundamental solution to the wave equation )is not concentrated on the light cone. Thus everything we see or hear would be accompanied by an (visual or acustic) echo, like the afterburn on a cheap TV screen. This would make vision, hearing and communication pretty difficult. Only in odd-dimensional spaces is a flash seen as a flash, too. Regards, HRG. ) which can be imagined as the light or sound emitted from a very strong and very small source, which is active only for a very small period. Then let all "very"'s go to infinity ....

04-30-2002, 12:54 PM	#6
wdog Veteran Member Join Date: Dec 2001 Location: Ohio, USA Posts: 1,547	Very nice Ip, I don't understand it all, for right this minute i am going to reserve the right to ask questions later.

Freethought & Rationalism Archive

The archives are read only.