Is Super Symmetry Dead? | Forbes

In summary, Super Symmetry (SUSY) is a theoretical framework that predicts the existence of particles that could solve some of the mysteries of the universe. However, after decades of research and experiments, no evidence of these particles has been found, leading to a decline in interest and funding for SUSY. While some scientists still hold out hope for its existence, the lack of evidence has led many to declare SUSY as dead.
  • #36
bluecap said:
Can you design a fundamental force of nature that has same symmetry breaking mechanism as proposed for SUSY

The fact that positive vacuum energy reflects spontaneous supersymmetry breaking is a direct consequence of the fact that local supersymmetry is an extension of local Poincaré symmetry, hence of gravity. Technically, this is because the stress-energy tensor ##(T_{\mu \nu})## in supersymmetric field theories is the image of the supersymmetry Noether's conserved current ##(S_{\nu \beta})## under the super-Poisson-bracket with the supercharge ##(Q_\alpha)##

$$
T_{\mu \nu}
\;=\;
\gamma_\mu^{\alpha \beta}
\{Q_\alpha, S_{\nu,\beta}\}
$$

so that the vacuum expectation value of the stress-energy tensor is

$$
\langle vac \vert
T_{\mu \nu}
\vert vac \rangle
=
\gamma_\mu^{\alpha \beta}
\langle vac \vert
\{Q_\alpha, S_{\nu,\beta}\}
\vert vac \rangle
$$

which hence vanishes if the vacuum state is supersymmetric, hence if supersymmetry is not spontaneously broken.

So the specific nature of spontaneous supersymmetry-breaking is a reflection of the special fact that (local) supersymmetry is an odd-graded extension of (local) Poincaré-symmetry, hence of gravity. Symmetries not related to gravity in such a way cannot show this effect.

I recommend going to the original articles, such as Witten 81, section 2. The graphics that you reproduce above originates in Fayet-Ferrara 77, Fig. 1 on p. 286 (38 of 86).
 
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  • #37
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
The fact that positive vacuum energy reflects spontaneous supersymmetry breaking is a direct consequence of the fact that local supersymmetry is an extension of local Poincaré symmetry, hence of gravity. Technically, this is because the stress-energy tensor ##(T_{\mu \nu})## in supersymmetric field theories is the image of the supersymmetry Noether's conserved current ##(S_{\nu \beta})## under the super-Poisson-bracket with the supercharge ##(Q_\alpha)##

$$
T_{\mu \nu}
\;=\;
\gamma_\mu^{\alpha \beta}
\{Q_\alpha, S_{\nu,\beta}\}
$$

so that the vacuum expectation value of the stress-energy tensor is

$$
\langle vac \vert
T_{\mu \nu}
\vert vac \rangle
=
\gamma_\mu^{\alpha \beta}
\langle vac \vert
\{Q_\alpha, S_{\nu,\beta}\}
\vert vac \rangle
$$

which hence vanishes if the vacuum state is supersymmetric, hence if supersymmetry is not spontaneously broken.

So the specific nature of spontaneous supersymmetry-breaking is a reflection of the special fact that (local) supersymmetry is an odd-graded extension of (local) Poincaré-symmetry, hence of gravity. Symmetries not related to gravity in such a way cannot show this effect.

I recommend going to the original articles, such as Witten 81, section 2. The graphics that you reproduce above originates in Fayet-Ferrara 77, Fig. 1 on p. 286 (38 of 86).

What range of energy in TeV do you think the Superpartners can be lurking?

Also is there a possibility or mechanism (complex as it may be) for the supersymmetry be between normal matter and mirror matter (these being direct counterpart of all our baryonic particles but only right handed and form perhaps 5% of the dark matter sector? See a thesis about cosmology and mirror universe... https://arxiv.org/abs/astro-ph/0312607

Perhaps each is in different vacuum or spacetime boundary or the thousands of mechanisms or possibilities or variants of models physicists can easily write such as for example in ArXiv?
 
  • #38
bluecap said:
What range of energy in TeV do you think the Superpartners can be lurking?

This I am really not the right one to ask or answer.

I do take interest supergravity, on the grounds that it has excellent theoretical motivation, and I appreciate the curious fact that KK-compactifications to 4d that preserve global ##N=1## supersymmetry happen to be those that are mathematically rich (CY-geometry, ##G_2##-geometry), whatever that may be telling us; but I notice that there seems to be no theoretical reason why these compactifications should be dynamically preferred, and that the folklore of their phenomenological motivations (hierarchy problem, gauge coupling unification, naturalness) is based on an essentially numerological attitude only.

This makes me want to recall that:

"The alternative to naturalness, often neglected as an alternative, is having a theory."

which is a great sentence that one finds in Kane 17, p. 56 (6-10).

Now Kane of course does assume ##G_2##-compactification, which, while certainly interesting in itself, seems to be lacking a dynamical explanation from within the theory; but that granted then the great achievement of him and his collaborators is that, based on this single assumption, they first of all try to and then to a remarkable extent succeed with working out the theoretical consequences systematically, by analysis of the theory. Even if the result eventually disagrees with experiment, we will have learned what the generic predictions of this model are, hence will have learned something tangible about 11d supergravity and its UV completion, while from much of the unsystematic by-hand susy model building entertained elsewhere we will possibly have to conclude in 50 years time to have learned little, besides the lesson that physics unconstrained by theoretical framework becomes arbitrary.

One of the theoretical insights that Kane and collaborators have been amplifying is that in this model the gravitino mass after susy-breaking sets the scale for the moduli and the superpartners, such that, in the words of Kane 17, p. 43 (5-1), the upshot is this:

"When supersymmetry is broken the gravitino becomes massive — the splitting between the graviton (always massless) and the gravitino is a measure of the strength of the supersymmetry breaking, and it sets the scale for all the superpartner masses.

"It is important to understand that there are two measures relevant to understanding supersymmetry breaking, one the scale at which it is broken (about ##10^{14}## GeV as described above), and the other the resulting gravitino mass. In the compactified M-theory case the gravitino mass is calculated, and comes out to be about 40 TeV (40 000 GeV). Sometimes even experts confuse these two scales if they are speculating about supersymmetry breaking without a real theory to calculate.

"Thus 40 TeV is the natural scale for superpartner masses. That is not a surprising number in a theory starting with everything at the Planck scale, but it is surprising if one expects the superpartner masses to be near the particle masses (all well below 1 TeV). The squarks and other masses are indeed predicted to be at the gravitino scale, tens of tera-electronvolts."

"The theory has formulas (‘supergravity formulas’) for all the masses. When one calculates carefully the masses of the superpartners of the gauge bosons that mediate the Standard Model forces they turn out to get no contribution from one large source, and the resulting value for the superpartners of the gauge bosons (gauginos) is about 1 TeV, rather than about 40 TeV. They are the gluino, photino, zino, and wino. The strong force gluino is heavier, about 1.5 TeV or somewhat more, and the electroweak ones (photino, zino, wino) are somewhat lighter, about half a tera-electronvolt. The lightest superpartner, which is important for how to detect the signals at the LHC and for understanding dark `matter, will be a combination of the electroweak ones, and thus about half a tera-electronvolt in mass. All of these are observable at the LHC in the run underway through 2018. That run is supposed to collect an amount of data measured in units called inverse femtobarns (##fb^{-1}##). At the time of writing (December 2016) it has collected about ##40 fb^{-1}##, and is into the region where we can hope for signals of gauginos. The goal for the LHC is to collect ##300 fb^{-1}## through 2018. Without a detailed theory to calculate with, we would not have had serious predictions for masses."

(from Kane 17, chapter 5).
 
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  • #39
My father used to study and research Supersymmetry.
We were talking, and he was saying that the field is dying out. Now, he studies dark matter and energy with another professor.
Just what he told me.
 
  • #40
ISamson said:
the field is dying out

Sure, that's a truism after the LHC results did rule out most of what people in the field had claimed would be seen.

On the other hand, just as an idea being fashionable does not make it true, so an idea being unfashionable alone does not make it false. The truth is more subtle than the common sport-event-like attitude towards it may indicate.
 
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  • #41
bluecap said:
In 1 Billion A.D. Can we already reach 10^16 GeV or say 3 Billion A.D.? How many billions of years later before we can probe the Planck scale?

Anyway. A hundred years from now.. when building more accelerators would no longer be viable due to financial, environment, political or military catastrophe. Can we at least do one last experiment never before tried (at least officially)...

There may be a Particle Desert where nothing occurs below 10^16 GeV and above those already explored. So let the last final experiment be about testing non-thermal based symmetry breaking. Perhaps all those missing particles would suddenly popping up. In many unofficial experiments now. They detected exotic particles even monopoles by initiating non-thermal phase transition but no other scientists want to even try duplicating any of it. So before we dismantle the last particle accelerator on Earth and before the last particle physicists get into other fields like banking or telecommunications industry.. can we at least try this one last experiment? Perhaps we would see results the world has never seen before..
I don't know what we could reach within 1 billion od years. First we should concentrate on surviving here on Earth for next thousand of years because our current actions may well result in an extinction much earlier than that.
Personally I believe that Planck accelerator could be built by Kardashev 3 civillization, eg one which could summon to intelligent use most of energy of entire galaxy.
IMO such civillizations don't exist and probably cannot exist.
Testing Planck energy interactions faces 2 major hurdles. First one and already an enormous challenge to accelerate particles to said energy is dwarfed by really unsurmonable problem of adequate *luminosity* of said accelerator.
Just think about hopelessly small effective crossections for collisions at Planck energy. After all you are probing distances in range of 10^-35cm. It have been calculated that one attempting to collect data from 10 such collisions (to get statistically significant results) would need to accelerate *lunar mass* of leptons or 0.01-0.1 of solar mass of hadrons to said energy, all in a reasonable time. That assuming that he could keep a beam 1um (!) wide.
So it is rather out of question. The best chance for such a device to be built is perhaps as a result of some sort of military arms race between 2 advanced Kardashev 3 civilizations. One could evaporate a planet by pressing a button over million of light years distance. Supermassive BH would be a power source, constellations of orbiting it neutron stars would be deflecting and beaming magnets/masses etc.
Mind you, the risk of causing quantum vacuum phase transition (and destruction of entire Universe within Hubble radius) would be substantial during such experiments, so a large degree of recklessness is a prerequisite for those attempting it. So reckless civillization would probably finish itself off long before getting there.

Practically I suspect that we might build 1 or 2 more generations of accelerators to get into 0.1 - 1 PeV of hadron energy (or 10-50 TeV for leptons). This will allow to investigate possibility of proton decay by electroweak process mediated by *sphalerons*. If no new physics, eg no new fundamental particles, are found meantime that is it.
Great desert will be considered proven and Standard Model with all its shortcommings will reign for good.

I cannot comment on "unconventional research". There is a slim chance that something worth attention is out there but it will rather go the same way like cold fusion research did. Mind you, conventional physics with string theories, multiverses and inflation is more and more religious like activity and insistence to work on it is a sign of decay of intellect. It is more and more unscientific. Peoples are insisting on beating a dead horse because they simply cannot admit that decades of their work are simply good for nothing. Peter Voit of Columbia University has something to say about it. Read his blog "not even wrong".

Bright part of the picture is that a lot is still to be discovered in *low energy* physics. Who knows, maybe at picokelvins (10^-12K) and below matter starts to behave in such a way that we are not suspecting it even in our wildest dreams. These conditions most unlikely exist *anywhere* in Universe (and never did) if not produced by intelligent beings.
Gravitational wave astronomy is another very promissing avenue.
So even if high energy physics hit its end, there is still a lot to learn.
 
Last edited:
  • #42
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
The fact that positive vacuum energy reflects spontaneous supersymmetry breaking is a direct consequence of the fact that local supersymmetry is an extension of local Poincaré symmetry, hence of gravity. Technically, this is because the stress-energy tensor ##(T_{\mu \nu})## in supersymmetric field theories is the image of the supersymmetry Noether's conserved current ##(S_{\nu \beta})## under the super-Poisson-bracket with the supercharge ##(Q_\alpha)##

$$
T_{\mu \nu}
\;=\;
\gamma_\mu^{\alpha \beta}
\{Q_\alpha, S_{\nu,\beta}\}
$$

so that the vacuum expectation value of the stress-energy tensor is

$$
\langle vac \vert
T_{\mu \nu}
\vert vac \rangle
=
\gamma_\mu^{\alpha \beta}
\langle vac \vert
\{Q_\alpha, S_{\nu,\beta}\}
\vert vac \rangle
$$

which hence vanishes if the vacuum state is supersymmetric, hence if supersymmetry is not spontaneously broken.

So the specific nature of spontaneous supersymmetry-breaking is a reflection of the special fact that (local) supersymmetry is an odd-graded extension of (local) Poincaré-symmetry, hence of gravity. Symmetries not related to gravity in such a way cannot show this effect.

I recommend going to the original articles, such as Witten 81, section 2. The graphics that you reproduce above originates in Fayet-Ferrara 77, Fig. 1 on p. 286 (38 of 86).

There seems to be 2 main focuses of supersymmetry. In Supergravity and the MSSM (Minimal Supersymmetric Standard Model) where wiki stated that:

"Theoretical motivations
There are three principal motivations for the MSSM over other theoretical extensions of the Standard Model, namely:

Naturalness
Gauge coupling unification
Dark Matter
These motivations come out without much effort and they are the primary reasons why the MSSM is the leading candidate for a new theory to be discovered at collider experiments such as the Tevatron or the LHC."

This seems to differ to Supergravity that also uses Supersymmetry.

1. If the Hierarchy Problem was solved by scale symmetry (see https://www.wired.com/2014/08/multiverse/ ) and dark matter was not caused by the lightest superpartner and the gauge coupling unification meeting at one point is due to hidden forces of nature. Then there is no need for MSSM to be at low energy (slightly above Higgs mass) meaning the Supergravity Supersymmetry could be at say 100 TeV. Is this what you meant?

2. Also if there is no weak scale MSSM and Supersymmetry only occurs above 100 TeV. Can this explain the gauge coupling unification meeting at one point?

3. Lastly. Can any hidden forces of nature mimic the same gauge coupling unification graph meeting at one point? What should be the behavior of the hidden forces of nature?

Hope you can address the 3 questions separately in your reply. Thanks :)
 
  • #43
ISamson said:
My father used to study and research Supersymmetry.
We were talking, and he was saying that the field is dying out. Now, he studies dark matter and energy with another professor.
Just what he told me.

What if axion or any dark matter particle would be undetectable too. Would dark matter die out too like supersymmetry? dark matter is required for cosmos wide gravity dynamics.. but is it not supergravity's Poincare invariance and supersymmetry being local symmetry is also required to exist to make gravity more solvable? or not? I'm interested in this because it seems besides spacetime and quantum fields.. we may need another third theory to combine them.. here supergravity may not even exist.
 
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  • #44
Martin0001 said:
I don't know what we could reach within 1 billion od years. First we should concentrate on surviving here on Earth for next thousand of years because our current actions may well result in an extinction much earlier than that.
Personally I believe that Planck accelerator could be built by Kardashev 3 civillization, eg one which could summon to intelligent use most of energy of entire galaxy.
IMO such civillizations don't exist and probably cannot exist.
Testing Planck energy interactions faces 2 major hurdles. First one and already an enormous challenge to accelerate particles to said energy is dwarfed by really unsurmonable problem of adequate *luminosity* of said accelerator.
Just think about hopelessly small effective crossections for collisions at Planck energy. After all you are probing distances in range of 10^-35cm. It have been calculated that one attempting to collect data from 10 such collisions (to get statistically significant results) would need to accelerate *lunar mass* of leptons or 0.01-0.1 of solar mass of hadrons to said energy, all in a reasonable time. That assuming that he could keep a beam 1um (!) wide.
So it is rather out of question. The best chance for such a device to be built is perhaps as a result of some sort of military arms race between 2 advanced Kardashev 3 civilizations. One could evaporate a planet by pressing a button over million of light years distance. Supermassive BH would be a power source, constellations of orbiting it neutron stars would be deflecting and beaming magnets/masses etc.
Mind you, the risk of causing quantum vacuum phase transition (and destruction of entire Universe within Hubble radius) would be substantial during such experiments, so a large degree of recklessness is a prerequisite for those attempting it. So reckless civillization would probably finish itself off long before getting there.

Practically I suspect that we might build 1 or 2 more generations of accelerators to get into 0.1 - 1 PeV of hadron energy (or 10-50 TeV for leptons). This will allow to investigate possibility of proton decay by electroweak process mediated by *sphalerons*. If no new physics, eg no new fundamental particles, are found meantime that is it.
Great desert will be considered proven and Standard Model with all its shortcommings will reign for good.

I cannot comment on "unconventional research". There is a slim chance that something worth attention is out there but it will rather go the same way like cold fusion research did. Mind you, conventional physics with string theories, multiverses and inflation is more and more religious like activity and insistence to work on it is a sign of decay of intellect. It is more and more unscientific. Peoples are insisting on beating a dead horse because they simply cannot admit that decades of their work are simply good for nothing. Peter Voit of Columbia University has something to say about it. Read his blog "not even wrong".

Bright part of the picture is that a lot is still to be discovered in *low energy* physics. Who knows, maybe at picokelvins (10^-12K) and below matter starts to behave in such a way that we are not suspecting it even in our wildest dreams. These conditions most unlikely exist *anywhere* in Universe (and never did) if not produced by intelligent beings.
Gravitational wave astronomy is another very promissing avenue.
So even if high energy physics hit its end, there is still a lot to learn.

We are still missing something big even at our everyday baryonic energy scale. I'm so curious how physicists could miss them that's why I'm interested in all these questions. Could it be because our particle physics treat particles at isolation and the ensembles would have different behavior. For example we may not detect dark matter using isolated particles but ensembles there may be an effect. Do you know the term for this ensemble approach in physics? Emergence?
 
  • #45
bluecap said:
There seems to be 2 main focuses of supersymmetry. In Supergravity and the MSSM (Minimal Supersymmetric Standard Model) where wiki stated that:

"Theoretical motivations
There are three principal motivations for the MSSM over other theoretical extensions of the Standard Model, namely:

Naturalness
Gauge coupling unification
Dark Matter
These motivations come out without much effort and they are the primary reasons why the MSSM is the leading candidate for a new theory to be discovered at collider experiments such as the Tevatron or the LHC."

This seems to differ to Supergravity that also uses Supersymmetry.

I had been commenting on this briefly in #38. Naturalness is mostly numerology. Interesting to read Kane 17, about naturalness:

"now the claims are based on calculations in actual theories, while in the past they were based on analogies or ‘naturalness’ arguments" (p. 14 (xii))

"Until recently there were no theories predicting the values of superpartner masses. The arguments based on ‘naturalness’ are basically like saying the weather tomorrow should be the same as today. The opposite of naturalness is having a theory. [...] Claims they [superpartners] should have been seen would be valid given so called naturalness arguments, but are wrong in actual theories. Many of us think that is a misuse of the idea of naturalness, but it is the fashionable use. " (p. 33 (3-2))

"Some arguments (‘naturalness’) can be used to estimate what values they [MSSM parameters] might have. If those arguments were correct some superpartners would already have been discovered at the CERN LHC. It would have been nice if the naturalness arguments had worked, but they did not. Since they were not predictions from a theory it is not clear how to interpret that." (p. 39 (4-3))

"The failure of naïve naturalness to describe the world tells us we should look harder for a theory that does, an ‘ultraviolet completion’. Compactified string/ M-theories appear to be strong candidates for such a theory. The alternative to naturalness, often neglected as an alternative, is having a theory." (p. 57 (6-1-))

Also the lightest superpartner (LSP) as a WIMP dark matter candidate is a model facing drastic constraints from experiment.

If one does actual computations in a theory of supergravity one finds instead (Kane 17, p. 53 (6-7)):

"The dark matter is not the lightest superpartner, but axions or candidates from hidden sectors are strong dark matter candidates."
bluecap said:
the Supergravity Supersymmetry could be at say 100 TeV. Is this what you meant?

The supersymmetry of supergravity is local supersymmetry, it need not manifest itself as global symmetry at all. This is just the graded-version of the statement that gravity itself is a theory of local Poincaré-symmetry, and there is no reason to expect to see global Poincaré symmetry. In fact we don't observe global Poincaré symmetry in the universe; one has to work hard to produce, in the laboratory, tiny patches that are approximately globally Poincaré invariant (a vacuum).
 
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  • #46
bluecap said:
What if axion or any dark matter particle would be undetectable too. Would dark matter die out too like supersymmetry? dark matter is required for cosmos wide gravity dynamics.. but is it not supergravity's Poincare invariance and supersymmetry being local symmetry is also required to exist to make gravity more solvable? or not?
You can always pull the "not detected YET"-card, of course. Your second question is vague. I don't understand what you mean by "solvable" and how it relates to your former question.
 
  • #47
haushofer said:
You can always pull the "not detected YET"-card, of course. Your second question is vague. I don't understand what you mean by "solvable" and how it relates to your former question.

I meant in the context of Woit's passage in "Not Even Wrong"'s "This would be a gauge theory and might give a new version of general relativity, hopefully one whose quantum field theory would be less problematics." from the paragraph:

"Another reason for being interested in supersymmetry was the hope that it might help with the problem of constructing a quantum field theory for gravity. One of the main principles of general relativity is what is called 'general coordinate invariance', which means that the theory doesn't depend on how one changes the coordinates one uses to label points in space and time. In some sense, general coordinate invariance is a local gauge symmetry corresponding to the global symmetry of space and time translations. One hope for supersymmetry was that one could some make a local symmetry out of it. This would be a gauge theory and might give a new version of general relativity, hopefully one whose quantum field theory would be less problematics."
 
  • #48
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
I had been commenting on this briefly in #38. Naturalness is mostly numerology. Interesting to read Kane 17, about naturalness:

"now the claims are based on calculations in actual theories, while in the past they were based on analogies or ‘naturalness’ arguments" (p. 14 (xii))

"Until recently there were no theories predicting the values of superpartner masses. The arguments based on ‘naturalness’ are basically like saying the weather tomorrow should be the same as today. The opposite of naturalness is having a theory. [...] Claims they [superpartners] should have been seen would be valid given so called naturalness arguments, but are wrong in actual theories. Many of us think that is a misuse of the idea of naturalness, but it is the fashionable use. " (p. 33 (3-2))

"Some arguments (‘naturalness’) can be used to estimate what values they [MSSM parameters] might have. If those arguments were correct some superpartners would already have been discovered at the CERN LHC. It would have been nice if the naturalness arguments had worked, but they did not. Since they were not predictions from a theory it is not clear how to interpret that." (p. 39 (4-3))

"The failure of naïve naturalness to describe the world tells us we should look harder for a theory that does, an ‘ultraviolet completion’. Compactified string/ M-theories appear to be strong candidates for such a theory. The alternative to naturalness, often neglected as an alternative, is having a theory." (p. 57 (6-1-))

This make sense. Ok. I'll get Gordon Kane book "String Theory and the Real World" https://www.amazon.com/dp/1681744880/?tag=pfamazon01-20

So in short, you agree all particles are superstring/solitonic excitations of the geometry of the space-time continuum? This makes sense too.. and if you consider E8xE8 where the second set is a shadow universe... then it make even more sense as it explains more of the world.. so I guess M-Theory would be a theory about the degrees of freedom to engineer and influence the space-time continuum like composing the music of superstrings such that you can create and uncreate reality as one sees fit. Then this makes perfect sense and the elusive Holy Grail Theory of Everything.

Also the lightest superpartner (LSP) as a WIMP dark matter candidate is a model facing drastic constraints from experiment.

If one does actual computations in a theory of supergravity one finds instead (Kane 17, p. 53 (6-7)):

"The dark matter is not the lightest superpartner, but axions or candidates from hidden sectors are strong dark matter candidates."

The supersymmetry of supergravity is local supersymmetry, it need to manifest itself as global symmetry at all. This is just the graded-version of the statement that gravity itself is a theory of local Poincaré-symmetry, and there is no reason to expect to see global Poincaré symmetry. In fact we don't observe global Poincaré symmetry in the universe; one has to work hard to produce, in the laboratory, tiny patches that are approximately globally Poincaré invariant (a vacuum).
 
Last edited:
  • #49
bluecap said:
I meant in the context of Woit's passage in "Not Even Wrong"'s "This would be a gauge theory and might give a new version of general relativity, hopefully one whose quantum field theory would be less problematics." from the paragraph:

"Another reason for being interested in supersymmetry was the hope that it might help with the problem of constructing a quantum field theory for gravity. One of the main principles of general relativity is what is called 'general coordinate invariance', which means that the theory doesn't depend on how one changes the coordinates one uses to label points in space and time. In some sense, general coordinate invariance is a local gauge symmetry corresponding to the global symmetry of space and time translations. One hope for supersymmetry was that one could some make a local symmetry out of it. This would be a gauge theory and might give a new version of general relativity, hopefully one whose quantum field theory would be less problematics."

This quote is a weird way to put it. First, supersymmetry is by definition a (graded) extension of spacetime Poincaré symmetry, and second gravity, and hence, supergravity, are induced by this, without need to appeal to any "hopes", by the usual first-order formulation of gravity.
 
  • #50
bluecap said:
Ok. I'll get Gordon Kane book "String Theory and the Real World" https://www.amazon.com/dp/1681744880/?tag=pfamazon01-20

You have heard of "Library Genesis", I suppose? Ask Google.

bluecap said:
So in short, you agree all particles are superstring/solitonic excitations of the geometry of the space-time continuum?

What do you mean by "agree"? Are we planning to write a manifesto where we declare "We hold these truths to be self-evident..."? ;-)

There are various models, inside various theories. By working out the predictions that these models make, we learn which are compatible with observation. I was pointing to Kane's book because it gives an informal exposition of one class of susy models, called the ##G_2##-MSSM, which proves wrong much folklore about supersymmetry and which keeps making the worthwhile point that no amount of philosophy (such as naturalness) can supercede the core principle of modern physics: Pick a theory, pick a model inside the theory, then do the computations.
 
  • #51
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
You have heard of "Library Genesis", I suppose? Ask Google.

I think it's not free at Library Genesis. So i'll just get a kindle copy later.

What do you mean by "agree"? Are we planning to write a manifesto where we declare "We hold these truths to be self-evident..."? ;-)

I meant to say... whether the punchline of superstring theory is that all particles are superstring/solitonic excitations of the geometry of the space-time continuum? Is this the right way to put it? Like I can tell my friends that Einstein wanted to make everything out of geometry. Superstring theory seems to fulfil his dream.

There are various models, inside various theories. By working out the predictions that these models make, we learn which are compatible with observation. I was pointing to Kane's book because it gives an informal exposition of one class of susy models, called the ##G_2##-MSSM, which proves wrong much folklore about supersymmetry and which keeps making the worthwhile point that no amount of philosophy (such as naturalness) can supercede the core principle of modern physics: Pick a theory, pick a model inside the theory, then do the computations.

I need to understand Sabine Naturalness arguments and also understand Supergravity so Gordon Kane book would be timely.

I finally got it what M-theory (or something like it) was all about. It's about explaining things that are currently not explained by physicists. What we need are guiding principles as road towards M-Theory just like Dirac uses guiding principle to derive the Dirac Equation. At least I can use this description to explain to my friends.. lol
 
  • #52
bluecap said:
I think it's not free at Library Genesis.

Think again!

bluecap said:
I need to understand Sabine Naturalness arguments

That's sweet. Sabine Naturalness meets Hermione Hierarchyproblem But better than reading essays arguing against other essays is to try to understand the technical details of the physics.

Regarding your question "What is string theor?" see my string theory FAQ
 
  • #53
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
Think again!
That's sweet. Sabine Naturalness meets Hermione Hierarchyproblem But better than reading essays arguing against other essays is to try to understand the technical details of the physics.

Regarding your question "What is string theor?" see my string theory FAQ

Ok. Before focusing on Gordon's book. Just want to resolve something in Woit's book that made me dwelled on it... it's about the cosmological constant and supersymmetry.. Woit says in page 178:

"If one extends the MSSM not only to a supersymmetric grand unified theory, but even further to a theory that includes supergravity, then in principle one has ta theory that describes all known forces, something every physicist very much desires. Unfortunately, this idea leads to a spectacular disagreement with observation.

The problem is yet again caused by the necessity of spontaneous supersymmetry breaking. It turns out that the quantity that measures whether supersymmetry is a symmetry of the vacuum state is exactly the energy of the vacuum. If the vacuum state is not invariant under supersymmetry, it will have none-zero energy. Recall that since we don't see equal-mass pairs of particles and their superpartners, the supersymmetry must be spontaneously broken. This means that the vacuum state must be non-invariant under supersymmetry and have a none-zero energy. The scale of this energy should be approximately the scale at which supersymmetry is spontaneously broken, which we have seen is at least a couple of hundred GeV. In supersymmetric grand unified theories, the vacuum energy will be much higher, since it will receive contributions from the grand unified energy scale."

(skipping the paragraph where he explains the fact that in Eintein's theory of gravity, general relativity, things are very different. The energy of the vacuum directly affects the curvature of space-time and occurs as a term in Einstein's equations that he called the cosmological constant)

(Woit continued or concluded on the topic about the SS and CC...)
"The value of the cosmological constant can be thought of as the energy density of the vacuum, or equivalently, the energy in a unit volume of space-time. Using units where all energies are measured, in electron-volts (eV) and distances in inverse electron-volts (eV^-1), the cosmological constant has units of eV4, and astronomers believe its value is or order 10^-12 eV4. In a supersymmetric theory, spontaneous symmetry breaking must occur at an energy scale of at least 100 GeV = 10^11 eV, and leads to an expected vacuum energy density of around (100 GeV)^4 = 10^44 eV4. So the hypothesis of a supersymmetry leads to an energy density prediction that is off by a factor of 10^44/10^-44 = 10^56. This is almost surely the worse prediction ever made by a physical theory that anyone has taken seriously. Supersymmetric grand unified theories make the situation much worse, since in them one expect contributions to the vacuum energy of order (2x10^16 GeV)^4 = 1.6 x 10^101 eV4, which is off by a factor of 10^113"

Urs. Readers would sink in the chair reading the above. My point is.. is it possible there is a missing third theory (or object or whatever) besides spacetime and quantum fields where these two are just emergence?
 
  • #54
bluecap said:
We are still missing something big even at our everyday baryonic energy scale. I'm so curious how physicists could miss them that's why I'm interested in all these questions. Could it be because our particle physics treat particles at isolation and the ensembles would have different behavior. For example we may not detect dark matter using isolated particles but ensembles there may be an effect. Do you know the term for this ensemble approach in physics? Emergence?
Emergence/Emergent properties is a term rather disliked in physics. It is an observation that a whole does not behave like a sum of its parts. It is seen by many as an evidence of our lack of understanding of something. Some higher order interactions are not understood. Ideas of emergence are for example dealing with problems like "from where consciousness came".
Returning to physics and dark matter. Obviously we can detect gravitational effects of ensembles of DM but we don't know what isolated units (particles) are. There was a hope that said particles are WIMPS, eg capable to interact by weak force in addition to gravity. SUSY particles were good candidates for a WIMP but none were found.
There is a possibility that DM particles are more elusive "GIMPS" which are inteacting only by gravity. In such scenarios there is practically no hope to identify these in foreseable future.
I would disagree with statement that physics tries to treat different objects (particles) in isolation. For last few decades there is a great push to unify all what we know in one TOE, which remains elusive.
It may well be a time to ask about possibility that "no feasible TOE, known or unknown is there". What if Universe simply does not work in such unified way, eg if at Planck scale erratic, non consistent results would be repetitively produced? What if mathematics is an inadeuate tool to describe physics and it only can get us so far?
Of course there is still much to learn within Standard Model.
Decay of baryons to leptons by sphalerons mediated process is one of most interesting examples.
"Death of SUSY" is really troubling. Theoretical physicists are running out of ideas in their pursuit and increasingly turning to metaphysics. Hence we have multiverses and similar animals.
 
  • #55
Martin0001 said:
Emergence/Emergent properties is a term rather disliked in physics. It is an observation that a whole does not behave like a sum of its parts. It is seen by many as an evidence of our lack of understanding of something. Some higher order interactions are not understood. Ideas of emergence are for example dealing with problems like "from where consciousness came".
Returning to physics and dark matter. Obviously we can detect gravitational effects of ensembles of DM but we don't know what isolated units (particles) are. There was a hope that said particles are WIMPS, eg capable to interact by weak force in addition to gravity. SUSY particles were good candidates for a WIMP but none were found.
There is a possibility that DM particles are more elusive "GIMPS" which are inteacting only by gravity. In such scenarios there is practically no hope to identify these in foreseable future.
I would disagree with statement that physics tries to treat different objects (particles) in isolation. For last few decades there is a great push to unify all what we know in one TOE, which remains elusive.
It may well be a time to ask about possibility that "no feasible TOE, known or unknown is there". What if Universe simply does not work in such unified way, eg if at Planck scale erratic, non consistent results would be repetitively produced? What if mathematics is an inadeuate tool to describe physics and it only can get us so far?
Of course there is still much to learn within Standard Model.
Decay of baryons to leptons by sphalerons mediated process is one of most interesting examples.
"Death of SUSY" is really troubling. Theoretical physicists are running out of ideas in their pursuit and increasingly turning to metaphysics. Hence we have multiverses and similar animals.

One or century from now. M-Theory would be perfected.. and I guess our era now is like the period even before the discovery of Maxwell's equations and light. So when we tried to imagine what physics was like before Maxwell or even Faraday. It's akin to the present time when compared to M-theory in 2300 A.D.

What's troubling though is the possibility that mainstream physics thinking it's particle desert and experimental confirmation would be 10^16 GeV away and there may be fewer and fewer physicists as decades come by. So there is still the possibility that come 2300 A.D. there would be no longer any theoretical physicists and no M-theory, especially if we face a dystopian future amidst a global thermonuclear exchange sometime in the future.
 
  • #56
bluecap said:
resolve something in Woit's book

You are holding on to a bad choice of information source there.

In perturbative quantum field theory the cosmological constant is a free renormalization parameter in an affine space of choices. See here for rigorous discussion. If one imposes the renormalization condition of supersymmetry this changes, but after supersymmetry breaking it is a free parameter in the effective field theory.

There are many reasons to be dubious about supersymmetry and superstrings as a model for reality. Unfortunately, public discussion tends to focuse on confused non-reasons.

Now that I understand which background you have (little besides some ill-chosen popular-level books, it seems!) I don't recommend reading Kane's book to you.

I wish there were a good popular-level book that I could point you to.
 
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  • #57
bluecap said:
One or century from now. M-Theory would be perfected.. and I guess our era now is like the period even before the discovery of Maxwell's equations and light. So when we tried to imagine what physics was like before Maxwell or even Faraday. It's akin to the present time when compared to M-theory in 2300 A.D.

What's troubling though is the possibility that mainstream physics thinking it's particle desert and experimental confirmation would be 10^16 GeV away and there may be fewer and fewer physicists as decades come by. So there is still the possibility that come 2300 A.D. there would be no longer any theoretical physicists and no M-theory, especially if we face a dystopian future amidst a global thermonuclear exchange sometime in the future.
M-theory is one of main branches of string theories. However I am here firmly with Peter Voit - string theories are not even theories.
They are predicting everything what possibly can be predicted, hence they are of no use. There is approximately 10^520 of possible discreet setups which string theories are predicting.
There are ~10^250 more possibilities of different string theories than a number of Planck volumes in Hubble volume and this is plainly speaking insane.
Recently some serious work have been done to find out what string theories are NOT predicting, eg is there any imaginable Universe setup which cannot be predicted by one of possible variants of string theory.

The only good thing which may come out of expected death of SUSY is that it kills most of string theories on the spot. Of course dieharders will claim that higher energy SUSY is out there and we have still 10^518 possible string theories but at least there is some progress here. They will have to accept that remaining string theories are ugly, unnatural and displeasing. Hierarchy problem will haunt them for good.

All other implications of death of SUSY for high energy physics are bad. Nothing new up to 0.1 - 1PeV would mean that we are going to close the shop and go home.
No institution would risk $ quadrillion or more (eg global GDP of 2 decades by today numbers) to build 1 EeV accelerator on Jupiter orbit if scientific advice is that most likely nothing interesting is going to be found. And from 1EeV to 10 XeV (Planck energy) there is a reassuring gap of hopelessness.

Perhaps we need to rethink our approach, abandon string theories to liberate intelectual potential of brightest peoples on Earth from chasing mirages and direct it to more fruitful areas of physics like GW astronomy where a lot is to be discovered. Who knows, maybe keen observations of GW will give an answer to questions where traditional accelerator building approach is no longer of use? This is our best hope to probe events where Planck scale is at play. Careful evaluation of data could for example reveal that just above expected event horizon there is a surface after all.
Or that under EH must be a Planck Star instead of singularity.
Wouldn't that be a wonderful breakthrough?
 
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  • #58
Martin0001 said:
M-theory is one of main branches of string theories. However I am here firmly with Peter Voit - string theories are not even theories.
They are predicting everything what possibly can be predicted, hence they are of no use. There is approximately 10^520 of possible discreet setups which string theories are predicting.
There are ~10^250 more possibilities of different string theories than a number of Planck volumes in Hubble volume and this is plainly speaking insane.
Recently some serious work have been done to find out what string theories are NOT predicting, eg is there any imaginable Universe setup which cannot be predicted by one of possible variants of string theory.

The only good thing which may come out of expected death of SUSY is that it kills most of string theories on the spot. Of course dieharders will claim that higher energy SUSY is out there and we have still 10^518 possible string theories but at least there is some progress here. They will have to accept that remaining string theories are ugly, unnatural and displeasing. Hierarchy problem will haunt them for good.

All other implications of death of SUSY for high energy physics are bad. Nothing new up to 0.1 - 1PeV would mean that we are going to close the shop and go home.
No institution would risk $ quadrillion or more (eg global GDP of 2 decades by today numbers) to build 1 EeV accelerator on Jupiter orbit if scientific advice is that most likely nothing interesting is going to be found. And from 1EeV to 10 XeV (Planck energy) there is a reassuring gap of hopelessness.

Perhaps we need to rethink our approach, abandon string theories to liberate intelectual potential of brightest peoples on Earth from chasing mirages and direct it to more fruitful areas of physics like GW astronomy where a lot is to be discovered. Who knows, maybe keen observations of GW will give an answer to questions where traditional accelerator building approach is no longer of use? This is our best hope to probe events where Planck scale is at play. Careful evaluation of data could for example reveal that just above expected event horizon there is a surface after all.
Or that under EH must be a Planck Star instead of singularity.
Wouldn't that be a wonderful breakthrough?

One message I read SUSY is alive.. one message I read SUSY is dead.. it's confusing lol.. at times like this.. Gordon Kane "String Theory and the Real World" may give some insight. I'll spend on it a few days and reflect and do soul searching on superstring theory. Meanwhile. I'll leave you experts to discuss this on harder levels. Thanks to all.
 
  • #59
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
You are holding on to a bad choice of information source there.

In perturbative quantum field theory the cosmological constant is a free renormalization parameter in an affine space of choices. See here for rigorous discussion. If one imposes the renormalization condition of supersymmetry this changes, but after supersymmetry breaking it is a free parameter in the effective field theory.

There are many reasons to be dubious about supersymmetry and superstrings as a model for reality. Unfortunately, public discussion tends to focuse on confused non-reasons.

Now that I understand which background you have (little besides some ill-chosen popular-level books, it seems!) I don't recommend reading Kane's book to you.

I wish there were a good popular-level book that I could point you to.

Just to inform you that Gordon Kane's book "String Theory and the Real World" is just what I needed to answer most of my questions about the connection of Supergravity, Hidden Sectors, M-Theory, Compactification, Supersymmetry and so much more. I understand each paragraph of it. So it's really the good popular-level book that many need (who are asking same questions I do). Note I had previously read so much about spontaneous symmetry breaking. I have read over 100 physics books. Btw Woit's book "Not Even Wrong" is actually harder than Gordon Kane "String Theory and the Real world".. For example Woit wrote in page 128 of Not Even Wrong:

"The Wess-Zumino-Witten two-dimensional quantum field theory turns out to be closely related to the representation theory of Kac-Moody groups. Just as the Hilbert space of quantum mechanical models gives a representation of any finite dimensional group of symmetry transformations of the model, the Wess-Zumino-Witten model has a symmetry group which is an infinite dimensional Kac-Moody group, and its Hilbert space is a representation of this group. The Hilbert space of the Wess-Zumino-Witten model is a representation not only of the Kac-Moody group, but of the group of conformal transformations (actually this is a serious over-simplification, but the Hilbert space can be decomposed into pieces for which this is true)."

Contrast this to Gordon Kane "String Theory and the Real World":
"Relativistic quantum field theory fails to provide a quantum theory of gravity for point-like particles. Treating particles as points is too singular. Probably any way of giving them extension would work; strings are just the simplest case"

Bottom line is. Kane book is just perfect. Got it at Kindle because it's not at Lib. Gen but it's worth it. So it's recommended for Martin0001 and others in this thread.

Anyway my comment about it and all is that. I think we are in similar situation as Einstein a hundred years ago. He tried to make Unified Field Theory when he hadn't considered the strong and electroweak force. So our physicists at this era is in simiar predicament. How can our present physicists make any unification when there are other forces or phenomena that are ignored.
 
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  • #60
bluecap said:
it's not at Lib. Gen

Right, sorry I had been wrong about this. Sorry for that. Glad that you like the book.
 
  • #61
Martin0001 said:
Emergence/Emergent properties is a term rather disliked in physics. It is an observation that a whole does not behave like a sum of its parts. It is seen by many as an evidence of our lack of understanding of something. Some higher order interactions are not understood. Ideas of emergence are for example dealing with problems like "from where consciousness came".
Returning to physics and dark matter. Obviously we can detect gravitational effects of ensembles of DM but we don't know what isolated units (particles) are. There was a hope that said particles are WIMPS, eg capable to interact by weak force in addition to gravity. SUSY particles were good candidates for a WIMP but none were found.
There is a possibility that DM particles are more elusive "GIMPS" which are inteacting only by gravity. In such scenarios there is practically no hope to identify these in foreseable future.
I would disagree with statement that physics tries to treat different objects (particles) in isolation. For last few decades there is a great push to unify all what we know in one TOE, which remains elusive.

When I described that physics tried to treat different objects (particles) in isolation. It's not in the context of unifying all in one TOE. I'll give you an example. When you study a human body in isolation. You detect the water molecules, the ligands, the mitochrondria or let's make the scale even smaller.. you detect the atoms in the body like oxygen, carbon, hydrogen, etc. Here you may not detect anything new. But when you view the entire body at once. There may be emergent properties (new physics) you can't detect individually.. what is the term for this macroscopic properties (maybe this is the term?)?

It may well be a time to ask about possibility that "no feasible TOE, known or unknown is there". What if Universe simply does not work in such unified way, eg if at Planck scale erratic, non consistent results would be repetitively produced? What if mathematics is an inadeuate tool to describe physics and it only can get us so far?
Of course there is still much to learn within Standard Model.
Decay of baryons to leptons by sphalerons mediated process is one of most interesting examples.
"Death of SUSY" is really troubling. Theoretical physicists are running out of ideas in their pursuit and increasingly turning to metaphysics. Hence we have multiverses and similar animals.
 
  • #62
@bluecap
Yes, I will pay attention to this book.
My main problem with string theory is that it does not make testable predictions at low, high or extremely high energies only produces more and more theoretical possibilities of different exotic vacua.
Not long ago we had 10^500 different possibilities, later 10^520 of them.
However there was significant progress made (which I was unaware of until yesterday) and now I have found that we have 10^272000 different possibilities.
https://web.northeastern.edu/het/string_data/about/
This is an insane number and of course 10^500 was also insane.
We are heading for major problems with string theory, namely it is more and more challenging to write a number of discreet vacua possibilities on a page of paper.
Usual exponential notation is hitting its limits. Perhaps tetrations and Knuth notation will come to rescue.
Good news are that theory might be falsifiable after all.
All what we need to do is to prove that number of discreet vacua possibilities is actually infinite and our low energy world came from one of infinite number of high energy worlds and it have arrived by one of infinite number of possible paths (or maybe by all of them at the same time).
At this point theory will be *renormalized*, eg discarded in its entirety and work will be directed into some other, more promising areas.

Major problem with string theory is one of *pride*. Pride of very bright peoples preventing them from admitting that they have been wrong.
 
  • #63
Martin0001 said:
@bluecap
Yes, I will pay attention to this book.
My main problem with string theory is that it does not make testable predictions at low, high or extremely high energies only produces more and more theoretical possibilities of different exotic vacua.
Not long ago we had 10^500 different possibilities, later 10^520 of them.
However there was significant progress made (which I was unaware of until yesterday) and now I have found that we have 10^272000 different possibilities.
https://web.northeastern.edu/het/string_data/about/
This is an insane number and of course 10^500 was also insane.
We are heading for major problems with string theory, namely it is more and more challenging to write a number of discreet vacua possibilities on a page of paper.
Usual exponential notation is hitting its limits. Perhaps tetrations and Knuth notation will come to rescue.
Good news are that theory might be falsifiable after all.
All what we need to do is to prove that number of discreet vacua possibilities is actually infinite and our low energy world came from one of infinite number of high energy worlds and it have arrived by one of infinite number of possible paths (or maybe by all of them at the same time).
At this point theory will be *renormalized*, eg discarded in its entirety and work will be directed into some other, more promising areas.

Major problem with string theory is one of *pride*. Pride of very bright peoples preventing them from admitting that they have been wrong.

Kane book has addressed the above.. in fact, the following passage is one of those I highlighted (it has address all my concerns which finally made me understand the field a bit better):

"If we want to test a theory of our world we have to find it and calculate its predictions. This is another issue where much that is said is confused. People talk of very large numbers of solutions of string theories, and claim will be difficult to find one that could describe our world among the huge number. In fact, compactified theories generically have many realistic features whose presence limits the number of possible theories. These features include gravity, Yang-Mills forces like the Standard Model ones, chiral quarks, and leptons that give parity violation, softly broken supersymmetry, Higgs physics, families, hierarchical fermion masses, neutrinos, inflaton candidates, a solution of the hierarchy problem, a solution of the strong CP problem, and more. Solutions with such properties are easy to find. There is still work to do to calculate sharp testable predictions and compare compactifications, but a reasonable amount of work is already done."

About your 10^272000 different possibilities. I think the shape of the Calabi-yau manifolds is programmed that way by some moduli dynamics. I mean.. there may be some more fundamental theory than superstring theory.. and these could be give the input or parameters to the Calabi-yau manifolds. This makes better sense.
 
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  • #64
Anyone who thinks that string theory has more solutions than usual for a physical theory, I invite to determine the number of solutions of these usual theories.

Exercise:

Consider usual Einstein-Yang-Mills-Dirac theory .

I)

FIx a semi-realistic gauge group and fermion content.

1) Does the theory have a finite number of solutions?

2) If not, does it have at least a finite-dimensional continuum of solutions?

3) If not, in which sense is the space of solutions smaller than the finite number ##10^{500}##? If it is?

II)

For better comparison with string theory, consider this question without fixing the gauge group and matter content. Hence consider the union of the spaces of solutions found in (I) as the choice of gauge group and matter content varies.

Can you get any handle on the size of the resulting "landscape" of solutions to usual Einstein-Yang-Mills-Dirac theory?
 
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  • #65
[URL='https://www.physicsforums.com/insights/author/urs-schreiber/']Urs Schreiber[/URL] said:
Can you get any handle on the size of the resulting "landscape" of solutions to usual Einstein-Yang-Mills-Dirac theory?
@Urs,
I will have to do some homework to make any intelligent comments on it.
All I may say at the moment is that quantum field theories dealing with low energy physics have a comfort to refer to experiment for verification of outcomes and string theories does not enjoy it.
I suspect that from initial 10^272000 of possible string theories we are going to get maybe 10^271500 and probably more possibilities which are going to give low energy world like we know.
So which one should we choose? First come, first served?
Mind you, with current peace of expansion of possibilities we may soon get to 10^^272000 possibilities. What then?
What would be for you a trigger to give up?

@bluecap,
"...There may be some more fundamental theory than string theory"
But any experimental evidence for it will be hidden under event horizons, somewhere at 10^400 GeV or so.
We won't get anywhere by "Russian doll theory" approach.
 
  • #66
Martin0001 said:
@Urs,

What would be for you a trigger to give up?
The money...
 
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  • #67
Try to focus on one thought at a time, not jumping randomly around the supply of woitianisms.

Let's agree that string theory is all wrong, so that you can focus just on the logic, not getting distracted by the sports competition spirit. What I would like you to do is understand just the logical fact, in itself, that it is rare in physics that a theory admits a finite number of solutions, and to understand the fallacy of thinking that any finite number, immense as it may seem, can be larger than the cardinality of the continuum.
 
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  • #68
Martin0001 said:
@Urs,
I will have to do some homework to make any intelligent comments on it.
All I may say at the moment is that quantum field theories dealing with low energy physics have a comfort to refer to experiment for verification of outcomes and string theories does not enjoy it.
I suspect that from initial 10^272000 of possible string theories we are going to get maybe 10^271500 and probably more possibilities which are going to give low energy world like we know.
So which one should we choose? First come, first served?
Mind you, with current peace of expansion of possibilities we may soon get to 10^^272000 possibilities. What then?
What would be for you a trigger to give up?

@bluecap,
"...There may be some more fundamental theory than string theory"
But any experimental evidence for it will be hidden under event horizons, somewhere at 10^400 GeV or so.
We won't get anywhere by "Russian doll theory" approach.

Martin0001, can you read this free preface of the book "String Theory and the Real World" now.. https://www.amazon.com/dp/1681744880/?tag=pfamazon01-20

then if you can't get it elsewhere.. buy the kindle version... it's only a 2 hours read the entire book.

I don't know your background. It's to have baseline and being updated of the latest. Then instead of criticizing Woit (whose stuff is more than a decade old). Try to critique Gordon's instead. I'll share some passage to get you going:

"Many experts who specialize in various aspects of string theory will not endorse the possibility that the final theory of our vacuum may be soon forthcoming, because they work in technical areas that lack overviews. Anyone who focuses on solutions in other than four dimensions, or black hole solutions, or anti-de Sitter space/CFT, or amplitudes, or moonshine, or many other areas will have no reason to expect a comprehensive theory to emerge. And of course solutions can be constructed that do not describe our vacuum. Similarly, experts in QCD physics or Large Hadron Collider (LHC) physics or dark matter physics will not have an overview of the ingredients described below, and generally will not be aware of the emerging final theory opportunity, Some who are not aware of it will be skeptical of it."

"Much has been written about the testability of string theories - we will see that compactified string/M-theory are indeed testable in the traditional way of physics theories, contrary to what is being said and written in a number of journalistic articles, blogs, and books"

Read the whole book now and please critique it. Thanks.
 
  • #69
@bluecap,
I have red free introduction. To say something of value I need to read entire book (will buy it and it will take some time to get - I live in Poland).

Nevertheless what I have found in introduction is already troublesome.

Author has a great hope that LHC will turn some evidence of dark matter particles and SUSY (book was published in 2017 and written probably earlier).
He acknowledges need to feel gaps in understanding of DM and SUSY, explicitly electroweak SUSY.
As we already know electroweak SUSY is rather out of question - it is not there according to LHC results.
DM particles are not detected either.
LHC results are pointing towards so called Great Desert - very bad scenario for those hoping to support BSM models by experimental evidence, btw possibility of such an outcome is acknowledged.

He is mentioning 2 successful theories upon which some unified theory could be built.
First is Standart Model of particle physics, second is Standart Model of cosmology.
With first I do not have any problem - it is very successful.
Second is a domain of speculations. Inflationary models of early Universe are heavily criticised by many prominent scientists, including those initially heavily involved in work on them (Steinhardt).
Inflationary models are not resolving hurdles they were meant to address, eg fine tuned initial conditions.
It have been shown that for fine tuning to be addressed by inflation, initial pre-inflation conditions would have to be even more fine tuned than without any inflation at all (Penrose).
On experimental front protons are still refusing to decay very much like sparticles are refusing to turn up.
Inflation is mainly kept alive to let peoples talk about something (beginning of Universe) even if actually they really don't know what they are talking about (as quantum theory of gravity is elusive) (Hossenfelder).
So at the moment I am not convinced that inflation based cosmology has a status of well supported theory. It is rather based on faith and wishful thinking (and yes, I am aware of results related to uniform CMB and flatness issue).

Finaly I observe that author is strongly convinced about possibility of unification of gravity with other forces.
What if Nature have decided the other way?

Of course to say anything more I would need to read whole book, not just an introduction.

Btw,
I do not criticize Woit. I agree with him. If you think that I criticize Woit then show me where.

@Urs,
Yes I understand your argument about large numbers and continuum.
The issue which Woit is rising is not only about large numbers of possible theories.
In QFT regarless of large numbers of possibilities some *simplest* assumptions related to gauge symmetry delivered a working theory. This is not true with string theories.
For example we have a continuum of numbers.
Ever wondered why numbers like 1,2 or 3 are somehow more useful in maths (or at least more often are turning in various equations describing Nature) than let's say number 5744869447463274733?
Nominally they are all equal after all.
QFT relies on simplicity of initial conditions to work and string theories are relying on large numbers from which something (hopefully) can be fished out.
He is also claiming that to make any variant of string theory resembling anything real one would need to put more and more information in and develope increasingly complex Calabi - Yau manufolds.
His point is that string theories are information neutral. You do not get out of string theory any more information about Universe than you put in.
Hence they are not useful.
It is not my intention to criticize your work or whatever. String theories have led to great developments in maths and yes there are some spinoffs helping in down to Earth physics. They do have practical applications.
However there are indications that these theories are unlikely to explain workings of Universe.
Don't you think that Multiverse ideas are subtle admissions of defeat?
 
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