1. Feb 18, 2018

### Martin0001

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 dont 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: Feb 18, 2018
2. Feb 18, 2018

### bluecap

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?

3. Feb 18, 2018

### bluecap

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.

4. Feb 18, 2018

### bluecap

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?

5. Feb 19, 2018

### Urs Schreiber

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."

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).

Last edited: Feb 20, 2018
6. Feb 19, 2018

### haushofer

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.

7. Feb 19, 2018

### bluecap

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."

8. Feb 19, 2018

### bluecap

This make sense. Ok. I'll get Gordon Kane book "String Theory and the Real World" https://www.amazon.com/String-Theor...8-1&keywords=string+theory+and+the+real+world

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.

Last edited: Feb 19, 2018
9. Feb 19, 2018

### Urs Schreiber

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.

10. Feb 19, 2018

### Urs Schreiber

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.

11. Feb 19, 2018

### bluecap

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

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.

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

12. Feb 19, 2018

### Urs Schreiber

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

13. Feb 19, 2018

### bluecap

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?

14. Feb 19, 2018

### Martin0001

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 dont 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.

15. Feb 19, 2018

### bluecap

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.

16. Feb 19, 2018

### Urs Schreiber

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.

17. Feb 19, 2018

### Martin0001

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?

18. Feb 19, 2018

### bluecap

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.

19. Feb 21, 2018

### bluecap

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.

Last edited: Feb 21, 2018
20. Feb 21, 2018