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Testing string theory with inflation July 5, 2007

Posted by dorigo in astronomy, news, physics, science.
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Yesterday morning there were several important talks scheduled in the plenary session at PASCOS, and the main conference hall was quite full.

I arrived late for the first talk, having had to pack and leave my room at the Radisson hotel. Sadly, in fact, my stay in London was designed to be short: basically limited to the three days bracketing the afternoon of my talk,  since due to travel fund shortages I had originally intended to pay this trip with money coming out of my own pocket (it ended up being fully financed anyway, but that’s another story).

So I made a fashionably late entrance in the hall, found a seat that did not involve bothering more than three people (there has to be a more rational way to arrange seats in a conference hall than a dumb laying them down in rows!), and set out to try and grasp something  from the second talk, virtual paper and pencil in hand (my faithful vaio):  Renata Kallosh, “Testing string theory by CMB“. Her thoughts on inflation and String theory are also described in a recent proceedings paper:  hep-th0702059.

I have to admit that most of what I heard, and frantically wrote down as if in a trance, does not really make much sense to me as I read it back now. However, one has to take into account the fact that as I write these lines I am blogging from a pub on Cromwell road, and I am well into my second pint of Foster’s. So  read the following with caution, and be aware that your reporter knows this matter at a *very* superficial level!

Renata gave an overview of inflation and dark energy as viewed from string theory. She noted that it was not possible to explain those features in string theory until recently, when the 2003 the new idea of flux compactification and moduli stabilization came forward, providing the solution through a landscape of vacua, some of them de Sitter vacua.

Having so many (here’s a understatement!) possible vacua is due to the ease with which you can make anti-de Sitter minima, which are supersymmetric. The problem of the negative cosmological constant can be circumvented by lifting the minima to de Sitter ones with a anti-D3 potential. I understood the graph she showed, but I admit I do not know how to write a anti-D3 potential. But brane theory was not part of my instruction, so I just admit defeat and move on.

Renata then went as far as to proclaim the following:  

“String theory has now one explanation of dark energy: a metastable cosmological constant with an equation of state w=-1. So far it is in agreement with data, and no compelling alternatives are available. Is it possible to rule out experimentally the positive cosmological constant as an explanation of dark energy ? This is an open question”.

To me, that seems a bit far-fetched, because it looks like string theory is getting tuned to experimental observations (a positive cosmological constant) and then claim it is “in agreement with data”. What detail am I missing ? I guess more than just a detail.

She then said that at present there are several models of inflation in string theory. They are flexible enough to describe a spectral index n_s = 0.95 (the spectral index is a number describing the tilt in the power spectrum of scalar perturbations from the cosmic microwave background – a value different from unity implying a violation of scale invariance), but they typically predict a low level of gravitational waves and low “non-gaussianity” (I admit to not know what non-gaussianity is, although I may have my own ideas). They may explain light cosmic strings.

She would expect that SUSY will eventually be discovered, and if that is so, one will be able to use the framework of 4-dimensional supergravity, and if possible derive it from ten- or eleven-dimensional M-string theory.  In case SUSY is found, the crucial future data for fundamental physics is the scale of gravitino mass: is it going to be at the typical scale of a LSP (light supersymmetric particle), at 1 TeV, or at 10^13 GeV ?

Then, another important unit is the detection or non-detection of tensor B-modes: the primordial gravity waves from inflation. One other sentence that startled me was the following:

“This model is extremely falsifiable, because it predicts no cosmic strings and n_s=0.95”.

It looks remarkable to me because the model in question seems to have been tailored around the findings of cosmology, and because falsifying a model by finding cosmic strings seems paradoxical to me. I feel that if we were to find cosmic strings, then ok, one particular model of string theory would be preferred rather than the others – but to me that would look like a detail. Again, I think I am missing something.

Then the speaker said there are other models, inflationary ones with large volume compactification. They require less fine tuning, but have more moduli, and more parameters. They also appear to have “nice predictive power”: they allow no gravity waves, no cosmic strings, and a value  n_s=0.96.  Well… Again, from my ignorant viewpoint, it looks to me as if string theorists, being unable to prove their construction through hard data, trick the rest of us into accepting the game of deciding which one among a class of string theory models better fits the experimental data which is used to construct them. Please now shoot me if I am letting too much of my negative thinking out…

 The talk went on. My notes are hard to decypher, and I will refrain from adding uncooked meat to this already confused post, and jump to a few concluding remarks.

She sees several possibilities for the future: after Planck produces its data, we will have to fit the spectral index n_s, and may find no tensor modes, no cosmic strings, no non-gaussianity:  in such case string inflation will already be in a good shape! Otherwise, if tensor modes are detected, it is a great challenge for string theory. If cosmic strings are detected, that appears to be not a problem: a welcome effect, and a potential window into physics at string scale. If no gaussianity is detected, some solution may be possible.

Renata concluded by recalling that when we learned that our universe is accelerating  it was a creative crisis, which forced physicists to reconsider many issues in string theory, including the one of moduli stabilization and metastable vacua. If tensor modes are found in the future, this may be equally important. It may provide us with information about the Kahler potential from the sky and force us to consider SUSY  phenomenology with a superheavy gravitino, or invent new methods of moduli stabilization.

Comments

1. island - July 5, 2007

The worst part of this is that these people won’t be called crackpots and cranks when all is said and done. But they should.

2. Kea - July 5, 2007

Fosters? Oh, no, Tommaso, that explains it! Surely she gave an entirely different talk …. this all just seems so unlikely.

3. Guess Who - July 5, 2007

Regarding non-gaussianity, I think there are a couple of experts on the subject near you:

http://arxiv.org/abs/astro-ph/0406398

If you read it, just remember Sarkar’s objection that CMB data can not simultaneously determine the primordial spectrum and other cosmological parameters,

http://www.ecm.ub.es/IRGAC2006/talks/120706/IRGAC06_Sarkar.pdf

As for cosmological string theory “predictions”, I have to agree. In the traditional sense of the word “predicition”, there are none. At “best”, you get statistical arguments for the likelyhood of measuring some quantity, based on conveniently defined measures (just keep trying till you come up with one which gives you the correct answer) in toy models of the landscape (because the real thing is way too hard to handle even statistically), as in

http://arxiv.org/abs/hep-th/0703206

The kind of work Kallosh is talking about is not even that. It’s a mish-mash of assuming that some combination of “distance between branes, size of internal dimensions, size of supersymmetric
cycles on which branes can be wrapped” will produce the desired set of scalar fields, combining those with a convient 4D SUGRA, assuming that the latter can somehow be derived as the low energy effective limit of a string theory model (instead of belonging in Vafa’s “swampland”), tuning it all to observation and then exclaiming: look, string theory predicts our universe! Well, duh.

There is virtually no end to the number of such constructions you could come up with, so it’s not like falsfifying one of them amounts to much. As a colleague of these people would have said:

“These are my predictions, and if you don’t like them… well, I have 10^500 others.”

4. island - July 6, 2007

Regarding non-gaussianity, I think there are a couple of experts on the subject near you:

http://arxiv.org/abs/astro-ph/0406398

Thank god the tachyon remains light throughout inflation!

What?!?

Oh brother, it’s no coincidence that efforts are always geared to “explain-away” the most apparent implications of the WMAP anomalies.

Is this Copernicus coming back to haunt us?… Thats Crazy!
-Lawrence Krauss

No, it’s willful ignorance.

5. Jason D. Padgett - July 6, 2007

Hello,

I’m a physics student in Washingotn state and I’m getting ready to publish some new equations that show EXACTLY where energy arises from. In addition it shows WHY E=MC^2, it solves Pi, shows a geometric pattern to prime numbers, creates spontaneous symmetry breaking, defines EXACTLY what eveything in the universe is moving relative to. It shows where sin, cos and tan waves arises from and where the geometry of spacetime itself comes from. It shows where the doppler effect arises from, and why everything is relative to the observer. It also shows WHY everything is a fractal and how to draw fractals using scalar multilple and vector addintion. Z=Z^2 + C is the long way to do fractals. There is a way to do it that is so simple I can teach small children (and I have) how to draw them. In fact, I can draw you a fractal of anything at all without using any fractal equation. (at least an equation in number form) All shapes are geometric equations. Any one interested in learning how, feel free to email me.

Sincerely,

Jason D. Padgett

6. dorigo - July 6, 2007

Hi Jason,

that’s great. I will read your theory once you get it published on a refereed journal. You said you are going to, right ?

Cheers,
T.

7. dorigo - July 6, 2007

Island, I agree – string theorists are in a superposition of very different states – future heros or future past-crackpots.

Kea, yes, fosters. But it was in the company of a stella artois.

GW, thank you for the links to preprints. And I agree, the impression I got is that, given there are 10^500 vacua, theorists are now feeling they have a free hand in producing 10^10 different versions of their theory, so that one of them is bound to “explain” w, r, n_s and the like. So much for falsifiability.

Cheers,
T.

8. me - July 6, 2007

You are absolutely right, it is not very predictive. As far as I understand, all of those flux vacua of KKLT have w=-1 so that’s a prediction if you like. If we detect a variation in the equation of state it will be interesting to see what happens to these anthropics.

I have never met an australian who drinks fosters or a belgian who particularly likes stella. Next time you are in london try something warm and flat.

9. dorigo - July 6, 2007

Thanks me, especially for the advice on the beer. I am probably not a good australian nor a good belgian, because I do like those two beers.

Cheers,
T.

10. island - July 6, 2007

I agree – string theorists are in a superposition of very different states – future heros or future past-crackpots.

Actually, my point was that they won’t be called crackpots when their math exercise is finally over, and that’s just wrong since they’ve been calling it physics and making claims about gravity, and supersymmetry, and, and, and…

A crank that’s wearing a sheepskin is still a quack… or something like that…😉

11. dorigo - July 6, 2007

Hi Island,

I had understood what your point was – I was introducing my own flavor to it. I think I prefer to keep the jury out on string theory, although I have my own ideas. If it is going to fail (quite likely) I think it is still interesting science, but of course not physics nor cosmology.

Cheers,
T.

12. island - July 6, 2007

I will read your theory once you get it published on a refereed journal.

This appeal to authority makes string theorists look like real physicists… for example…😉

13. island - July 6, 2007

I was introducing my own flavor

I should have picked up on your, eh… “quarkiness”… heheh

14. Alejandro Rivero - July 6, 2007

Actually, Jason D. Padgett said that there was an email for us to write him, but no email was given and in fact the name does not exist in the physics-related internet. On the other hand, I always welcome unsolicited email: try al.rivero@gmail.com but we aware I do not acept claims about stolen ideas😉 so I would strongly suggest to date-stamp in a reliable source of chronology if you do not want to remain anonymous. Or, I could argue that your ideas are a consequence of string theory and to give string theoretists all the merit.

15. Guess Who - July 6, 2007

It’s good to see that I am not the only sarcastically challenged person around…

16. dorigo - July 6, 2007

GW, it’s good to be gullible. By being such, one shows others he is intellectually honest and expects others to behave the same way…

Alejandro, that’s nice that you propose yourself as a crackpot-tester. It is a commendable activity in this world of true crackpots, false true-crackpots, and true false-crackpots.

Cheers,
T.

17. tulpoeid - July 7, 2007

Now, one thing that bothers me is string physicists talking as if strings (not to mention susy) is already well-established and we only wait to see which variation is correct, as was already pointed out here.
Another thing is them talking, in somewhat inverse proportion to the time left until the “first day”, about how the LHC will look only at isolated points of the mssm parameter space instead of “continua”, and this won’t be able to exclude it for good!!!

18. riqie arneberg - July 7, 2007

I’m a physics student in Washingotn state and I’m getting ready to publish some new equations that show EXACTLY where energy arises from. In addition it shows WHY E=MC^2, it solves Pi,………..

Try Art Bell’s call in show…………i dont suppose you have a perpetual motion machine as well?

19. Fred - July 7, 2007

I don’t know, Jason …

The fractalization of the brain is a terrible thing to waste (not including one’s drinking habits, of course). Show me how to draw a nice head of broccoli that I can sell for a couple of grand and I might be interested in your on-line art instructions.

20. island - July 7, 2007

It is a commendable activity in this world of true crackpots, false true-crackpots, and true false-crackpots.

That must be what it is… String theorists are NOT EVEN crackpots.

Okay, that’s enough out of me about stringers… for this minute, anyway, and certainly the jury is still out, but…

Now for the Loopers!…😉

FYI, anybody that wants to free me from my crank bondage can click on my name and shoot down my first post.

21. Bee - July 7, 2007
22. Thomas D - July 10, 2007

‘What detail am I missing?’ …

The first point you missed is the equation of state of the ‘dark energy’ which may or may not be a cosmological constant. This is described by the ratio of pressure to density w. Both Bond’s and Albrecht’s talks went into details about how w could be measured both now and in the future.

For a cosmological constant w = -1; for anything else, the value may be different. If convincing evidence of non-constant vacuum energy (or matter with large negative pressure not equivalent to a cosmological constant) were found — if w were shown not to equal -1 — most of the ideas of vacuum statistics in the ‘landscape’ would have to be thrown out, or at least they would be useless to explain the observed state of things.

There are more experiments testing the nature of the apparent ‘dark energy’ all the time, they get (slowly) more precise, and so far they don’t rule out the cosmological constant, although they might have done. In the next few years they might also rule out the cosmological constant. If this happens then current ideas about the ‘landscape’ will have been tested!

As for inflation: there is a very simple way to think about it. The amount of gravitational waves and non-gaussianity is related to the size of the inflationary potential energy and the distance the inflaton field moves in Planck units. (This is the ‘Lyth bound’.) In almost all the string models that people have some handle on at the moment, these are small or very small numbers. If one of these numbers is measured and is not very small, almost all of these models will have to be thrown away.

One point Kallosh made is that there are relatively few types of model where the connection to string theory is explicit. Certainly much fewer than in field theory where there is a continuous infinity of models… in fact an infinite-dimensional parameter space, since the inflation potential in field theory is a free function.

23. Guess Who - July 10, 2007

Thomas D, you have a valid point about w = -1 (also pointed out by “me” in comment #8). A cosmological constant, whether truly constant or just the bottom of a false string theory vacuum, would have w =-1, other mechanisms might not.

However, your comparison of the string theory landscape with the “continuous infinity of models” in field theory is misleading, as is your claim that “the inflation potential in field theory is a free function”. What you say is only true in classical field theory, and surely even most cosmologists have heard by now that nature is not classical.

When you require that your field theory make sense as a quantum theory, starting with the requirement of renormalizability, most classical field theories fail the test. A scalar field potential, to take the obvious example, had better contain at most quartic terms. So if you see a cosmologist having fun fitting a scalar potential containing higher order terms to the expansion history, you know that he or she can not be thinking of a fundamental theory, but just of an effective low energy approximation to some more fundamental theory. Problem is, the existence of that more fundamental theory is just an unproved assumption.

There is a parallel to the string-inspired work talked about by Kallosh, and it is not a good one: in this kind of work, it is assumed that the 4D SUGRA + assorted fields being used can be derived from string theory, i.e. that they are a low energy effective theory coming out of some point in the landscape (which in turn is arrived at assuming the validity of 10D SUGRA as an effective field theory valid in the perturbative regime of string theory, whatever that really is…). As in “field theoretic” inflationary model building, the whole thing therefore ultimately rests on an unproved and, a priori, wildly unlikely assumption. Personally, I do not find such work particularly meaningful. It may be instructive to build a model or two just to establish that it can be done, but taking it beyond that is a complete waste of everybody’s time and of tax payer’s money. Doing it as a hobby on one’s own time is of course beyond reproach, but people doing it “professionally” are… well, to put it diplomatically, they are in dire need of a reality check.

24. dorigo - July 11, 2007

Thomas,

thank you for your clarification… But I need to study the matter more before I can say I do understand the matter to a satisfactory level.

GW, I agree with your diplomatic statement!

Cheers,
T.

25. Jason D. Padgett - July 31, 2007

Hello again from Jason Padgett,

I just got back on the internet and read some of the comments posted. I’m in Pskov Russia right now showing my theory to some local mathematicans. I understand the doubts that many have about the claims that I have made. It seems to good to be true but I will challange any one to find a prime number that does not land on my geometric prime pattern. In fact, I would encourage you to test it, because the more asymmetric primes and any asymmetric primes to ANY power that you throw at it will always land on specific vectors. The prime number pattern has been missed for so long because many scientists think of numbers as writing/symbols (we made that up). The key to understanding primes is to understand the geometry of numbers and that primes have a LACK of symmetry. Remember that numbers are NOT REAL, they are always describing geometry. Numbers literally are geometry, or more specifically, numbers are planck constants (h-bar). Just like when you translate from one language to another you can lose a little of the meaning in the translation , so to is true for standard mathematics. Math, we invented. Geometry is pure. There is no predictable pattern to the numbers, themselves, but you CAN predict what vectors they will land on (relative to the observer). For instance, if you slice a circle into 30 segments and simply count in a circle you will see that every asymmetric prime (asymmetric primes=seven and above. 2, 3 and 5 are the primes of symmetry) and every asymmetric prime to ANY exponent will land on vectors 1,7,11,13,17,19,23,29. This pattern has been found before but the importance of what it does was not interpreted correctly. What it does is create spontaneous symmetry breaking. In other words, what everything is moving relative to. A good way to think of this problem is to imagine yourself in the vast emptiness of space with nothing around you for infinity. How can you tell if you are moving 1 cm/sec or 1,000,000,000 cm/sec? There are no trees rushing by you, no wind in you hair, nothing to compare yourself to to give you benchmarks for measurement. You need different things to compare to be able to make ANY measurements whatsoever. Another way (and I think the best way) to think of it is to picture a flawless sphere. If nothing exists but this flawless sphere (or wave) then how can you make any measurements? A perfect sphere looks the same no matter where you observe it from. So if you move from point A to point B how can you tell how far you have moved?….This is how. You use the geometry of prime numbers. If you are going to doubt this then I would ask that you check it for yourself before you say that it does not work because it ALWAYS works and we have tested it at my college to TEN BILLION and every asymmetric prime and and asymmetric prime to exponents yeilding an answer less than ten billion ALL land on these vectors. It is just adding/counting with shapes, the math is very simple, it is seeing the geometry that was difficult.

Here is the easiest way to understand how spontaneous symmetry breaking occurs. We will start with the easiest way. Draw a circle and slice it into 30 segments (or segments of Pi/15). Now write numbers 1,2,3….in each of the segments. Once you get to thirtyyou will write 31 above the number one. (basically another circle around the first) and continue this until say three or four hundred. Then if you like you can color in the prime with red or some bright color (to make them obvious to see. Notice how they land on the same vectors? Further notice that the pattern that they land on in the vectors is DIFFERENT and UNIQUE. In other words, if you count primes on the vector of one (or Pi/15) you will see that they fall in a pattern (from the radius outward like morse code, not prime=1, prime=31, prime=61, not prime=91, prime squared=121, prime=151 etc, Now compare this vector to the vector of seven (or theta=7Pi/15). Primes on this vector from the radius outward fall in a different pattern, 7=prime, 37=prime, 67=prime, 97=prim, 127=prime 157=prime 187=not prime. Now compare all the prime vectors with each other in this way. The pattern that the primes fall on each vector is UNIQUE. Now if you think of the perfect sphere problem using these prime vectors you can then have perfect symmetry of shape BUT have asymmetry of pattern of primes within perfect symmetry of shape. And different things can be compared to give you benchmarks for measurement. You can then observe a perfect sphere and move from point A to point B and say “I have moved from A to B ‘relative’ to my prime vectors.”

This is grossly oversimplified but right now I don’t have too much time to type. I have geometric drawings of the pattern that I will email you if you like. In addition to the equation for the creation of energy.

I will give you a hint about the equation for the creation of energy though. It comes from the Planck constant and uncertainty. Planck’s (or h-bar) as you I’m sure already know vibrate at the speed of light, correct? Well in a perfect sphere, (made with Planck constant and vibrating from uncertainty), there are specific points where the Planck collide head on with each other (relative to the radius). This is EXACTLY WHERE C^2 comes from in Einstein’s beautiful E=MC^2.

I will write more later but I hope this helps at least a little with understanding this strange new way of seeing numbers.

Sincerely,

Jason D. Padgett
Tacoma, Washington
email- jasonquantum1@yahoo.com

26. James Carnell - August 26, 2008

I am horrible w/ math and was just looking around for stuff on factoring numbers with waves (and was curious what a planck distance was). By using a circle, isn’t this like using base 15, base 30 etc. I have seen graphs of this before. Again I really don’t know much in this area so maybe this anooying or feeding trolls or I am a troll who knows…

http://www.brooksdesign-ps.net/Reginald_Brooks/Code/Html/pin2.htm


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