I was at a meeting in Princeton a short while ago, a small and focused workshop for people who are working on fundamental questions in inflationary cosmology. I hope to talk more about the meeting once the website is up (talks were not recorded), but here’s a simple question: what is the likelihood you would attach to the idea that some form of cosmic inflation occurred in the early universe?
My answer was 75%, which I thought was generous. It’s very hard to give a high probability to a speculative theory about what happened at energy scales to which we currently have no experimental access. But I found myself on the low end of opinions at the meeting, where the median was about 90% confidence. Of course, these are people who work on inflation professionally, and have chosen to do so. When I came home to ask the same question of my lunch crowd at Caltech, the answers were more like 25%.
An interesting glimpse into the non-unanimity of scientific opinion when it comes to untested theories. So, just for fun, let’s ask what your personal likelihoods are for the following theoretical ideas.
- Inflation
- Supersymmetry
- String theory
- Some form of Higgs boson
- Large extra dimensions
- WIMP dark matter
- Any non-cosmological-constant explanation for cosmic acceleration
I’m not defining these very carefully, and let’s posit that we’re not interested in weaseling about what the definitions mean. We’re asking what you think the probability is that, if you were to ask an omniscient being who knew everything about the workings of Nature whether these ideas were part of how the world works, would they answer in the affirmative. What do you think? (It’s helpful if you say a bit about what kind of perspective you are coming from.)
Physics theory grad student at caltech…
Inflation — 50% there are many possibilities to explain cmb homogeneity.
Supersymmetry — 90% probably extended (4-fold) supersymmetry.
String theory — 10% (of producing a falsifiable prediction in my lifetime…;) )
Some form of Higgs boson — 60% some form is pretty broad. There may be a simpler theoretical interpretation for SSB in the future.
Large extra dimensions — 0% or my shoe laces would untie
WIMP dark matter — 100% even if we can never detect it and even if it’s not most of dark matter
Any non-cosmological-constant explanation for cosmic acceleration — 100% non deterministic explanations for cosmological things in progress make no sense. There is a more complicated mechanism occurring here. My best guess is that gravity becomes repulsive under some condition, maybe from some dodgy global gauge symmetry violation. Maybe a hierarchy of force bosons.
Just ideas.
The people giving string theory as more likely than supersymmetry are the ones that confuse me.
“the median was about 90% confidence. Of course, these are people who work on inflation professionally, and have chosen to do so. ”
This sounds a bit like self-selection bias
I started putting together a chart of this since someone wanted a graph of the options (a poll really wouldn’t have covered it).
You’re welcome to add yourself. The countif should cover about 50 or so entries, so you don’t need to edit the totals, but if you need a new value you can insert a row.
https://spreadsheets.google.com/ccc?key=0AtHIstgQtFFidDN5bEdmem5iQlVMZGtGOXpud2pRaGc&hl=en&authkey=CNHV27YD
An amateur physicist, I come in about the same as MPS-17, with a higher probablility for TEV Susy of at least one particle (50%) and Higgs (90%). Somebody asked about the probability of LQG, which I put at 10^-n, as n grows infinite.
Okay, what confuses me is all the people putting string theory below 40%. How can you be so confident it’s *wrong*? I suspect people don’t like it because it’s not testable or it’s ambiguous or whatever, but if that’s the case I would think you would want to be in the 40% to 60% range.
I’m curious, what does #7 really mean? I know the others but that one confounds me. Would that include “there’s just more regular old matter than we can see, no magic particle or dimensions needed”.
1. Inflation – 75%
2. Supersymmetry – 70%
3. String theory –60%
4. Some form of Higgs boson – 75%
5. Large extra dimensions – 40%
6. WIMP dark matter – 25%
7. Any non-cosmological-constant explanation for cosmic acceleration – 1%
I put string theory below 50%. I read The Elegant Universe and recognized a serious flaw in one part, and a lack of explanation for, as an example, how an electron can emit a photon and still be an electron afterward. The flaw was in the illustration of the worldsheet of two merging strings. It was stated that the curvature of the worldsheet at the merging preserves Heisenberg uncertainty, because in different reference frames the merging would take place at different locations in space-time. That’s unconvincing anyway (because the HUP is supposed to work within one reference frame), but what’s worse, having the merger take place at a smooth curve instead of a corner implies that the strings move at infinite speed at that moment.
–Matt B., BS (Physics)
1. Inflation – 85%
2. Supersymmetry – 80%
3. String theory – 60%
4. Some form of Higgs boson – 33%
5. Large extra dimensions – 10%
6. WIMP dark matter – 95%
7. Non-cosmological-constant – 50%
1. Inflation: 90%
2. Supersymmetry: 50%
3. String Theory: 15%
4. Higgs: 80%
5. Large extra dimensions: 5%
6. WIMP dark matter: 99%
7. Non-cosmological constant: 20%
Coming at this from the perspective of cosmological data analysis. So a lot of these things I have relatively little knowledge of. But that doesn’t mean I can’t pull numbers out of my keister, does it?
This is a great post. Commenters definitely need to put credentials though (thanks to those who did).
Can we get this list emailed to a hundred (or so) respected physicists? I’d would LOVE to see the results.
1 Inflation – 25%
2 Supersymmetry – 25%
3 String theory – 10%
4 Some form of Higgs boson – 95%
5 Large extra dimensions – 10%
6 WIMP dark matter -95%
7 Any non-cosmological-constant explanation for cosmic acceleration – 10%
Street cred: 1st year physics grad student. Highly biased towards hoping everything is wrong and there is lots for me to discover 🙂
Graduate student in astronomy here.
1. Inflation: 75%. This is something of semantics because it depends on what you mean by inflation. The currently-favored slow-roll model makes a lot of sense in terms of the data, but the details are a bit murky to me. Constraints on the inflaton potential seem to me to be problematically based on the assumption that the only way to get the deSitter solution we seem to be after is through this kind of appeal. The question is, will we discover the inflaton in my lifetime? Perhaps, but looking back at past history of science lessons makes me think that something fundamental may be missing from the picture. I guess the best analog might be (in my mind) something like phlogiston and caloric theories of heat. The proper understanding of thermodynamics didn’t occur until we broke free of a certain conceptualization of the phenomena of temperature and heat. This is not something I think will necessarily happen for inflation, but I give it a 25% chance or so that such a paradigm shift will occur. However, I find it difficult to imagine an explanation from the FLRW perspective that would not have some sort of deSitter-like phase in the early universe at the time of inflation. Would it necessarily BE inflation though? That’s something of a semantics question. I would say “yes”, but, then, we could also argue that the fact that we still measure heat energy in “calories” means that the “caloric theory” wasn’t overthrown completely (and, indeed, it wasn’t… many of the conceptual understandings from heat flow are still used even though we understand there is no “caloric”).
2. Supersymmetry: 75% I take my cues from the prediction that anti-matter existed. The parallels between the two are too uncanny for me to argue that supersymmetry is false. If supersymmetry is false then I think that we’ll have bigger problems with beyond-standard-model particle physics that will make this a bigger issue than simply lacking supersymmetry. Still viable alternatives seem to be around, so I’ll give it the same shake I gave inflation.
3. String theory: 50% Not sure. On this one. I give it even odds for being correct or incorrect. As a unified theory, it seems to have made the most progress, but I’m not convinced that a fundamental flaw won’t be stumbled upon in the future. I give it a 50-50 shot of survival lacking so much information (since its observable implications are still being worked out).
4. Some form of Higgs boson: 95%: The standard model of particle physics is just too successful for me to give this much chance of failure. I’m not even aware of alternative methods for doing what the Higgs does. I keep the 5% chance of “incorrect” just to hedge my bets. Some may note that the same argument I made about the possibility of inflation being incorrect could be made here, but I think the correct comparison here is not to thermodynamics but to the particle physics experiments of the 20th century where the entire zoo of fundamental particles was predicted and discovered from the fundamental physics of the standard model. There’s no instance of the standard model predicting a particle that doesn’t exist, so I propose that if the standard model predicts it, the particle is probably there. If the Higgs turns out to be the inflaton, I’ll be pretty impressed, but I think we’ve almost ruled that out even not having observed it. Am I correct in that?
5. Large extra dimensions: 5% Too much work says “no” to this one. What’s left that hasn’t been ruled out is just too big of a leap for me. Still, I hedge the bet and give it a 5% chance.
6. WIMP dark matter – 90% Slightly less certain of this one than the Higgs boson but still pretty much convinced that this stuff has to exist with the forms described in standard WIMP theory. However, I’m not sure I’d take a bet on when direct detection would take place. To some extent, WIMP dark matter suffers from the same critique as the inflaton above with the difference that WIMP dark matter has a ton of observational data and falsified alternatives upon whose shoulders it stands.
7. Any non-cosmological-constant explanation for cosmic acceleration: 20% I think I know what you mean here: anything that does not have the rough form of w ~= -1. Quintessence, I suppose, counts too. Rocky Kolb has made a good case that we only have one really strong argument for dark energy and that’s supernovae Ia redshift-distance relations (the other piece of evidence being so-called “cosmic subtraction”). I don’t think he’s right, but his point is well-taken enough by me to give him a better chance of being correct than large extra dimensions, Higgs-alternatives, or dark matter alternatives. Incidentally, the fact that this percentage plus the percentage for 1) is 95% is somewhat comforting to me. I find the parallels between inflation and dark energy to be a bit too beguiling.
Thanks for the fun survey, Sean.
1. Inflation: 65%
2. Supersymmetry: 80%
3. String theory: 50%
4. Some form of Higgs boson: 90%
5. Large extra dimensions: 80%
6. WIMP dark matter: 45%
7. Any non-cosmological-constant explanation for cosmic acceleration: 30%
I’m a layman basing these percentages on what I’ve read.
1) Inflation: 85%
2) Supersymmetry: 85% at some scale, but only 50% that it’s at the weak scale
3) String theory: 10%
4) Higgs Boson of some sort: 99.9%. I’ll eat my hat otherwise.
5) Large Extra Dimensions: <1%. Sure, it's exciting that string theorists developed a way to make a testable prediction, but that's not a good reason to think that strings aren't all at the Planck scale
6) WIMPs: 45%. Axions are a very viable competitor
7) non-cosmological constant dark energy: 75%. After all, it can't be a cosmological constant, because that wouldn't conserve energy—right, Sean? 😉
1.Inflation – 85%
2.Supersymmetry – 25%
3.String theory – 40%
4.Some form of Higgs boson- 80%
5.Large extra dimensions – 10%
6.WIMP dark matter – 25%
7.Any non-cosmological-constant explanation for cosmic acceleration – 15%
I’m an amateur astronomer with a M. Sc. in Electrical Engineering. My job is in the Biotech and Pharmaceutical industry, but I try to keep up on what’s happening in astronomy, cosmology and physics in general.
1. 80%
2. 1%
3. 1%
4. 55%
5. 1%
6. 30%
7. ?
Astrodynamicist with background in physics.
Postdoc, on the hep-ph end of the spectrum….
1. Inflation
90%, although I’m not a cosmologist and have to admit some of this confidence might just be a matter of “well, I don’t have a better idea.”
2. Supersymmetry
MSSM at the TeV scale? 75%. Of that: 75% that it’s broken at the intermediate scale (some form of gravity mediation), 25% it’s low-scale breaking (gauge mediation).
(Note: my sense of likely breaking scale has been pretty time-dependent lately. It’s on the move toward an increased belief in intermediate scale breaking, but I’m still too uncomfortable with sequestering to put a number over 75% right now. Could be very different in a month or two, almost certainly in the direction of increased belief in gravity mediation.)
3. String theory
90%+, if, for instance, M-theory compactifications are also included. Mostly, I have high confidence that any consistent theory of quantum gravity will look a lot like the ones we already have, and at least some people will call it “string theory” in the end….
(Also, I think the AdS/CFT case that reasonable theories of quantum gravity look a lot like string theories is much stronger than most people tend to emphasize.)
4. Some form of Higgs boson
100%. If you require that WW scattering is unitarized dominantly by these bosons, and not, e.g., by something like a technirho, I’ll go with 90%.
5. Large extra dimensions
0.0001%, if you mean something visible at the TeV scale. Maybe 5% if you would count, say, large-volume string compactifications with the string scale at the intermediate scale, which would show up mostly as SUSY at the LHC. (Volume ~ 10^14 in string units, or something like that…)
6. WIMP dark matter
51.25%. That is: 50% given gravity mediation (see above), 5% given gauge mediation (see above), 50% if no SUSY at the TeV scale. (I initially wrote a much larger number given gravity mediation, then I stepped back and considered whether I was willing to bet on definitely more energy density in WIMPs than axions.)
7. Any non-cosmological-constant explanation for cosmic acceleration
Awkward. Any cosmological constant should be determined by some potential, in the sense that there are always scalar fields fluctuating around the vacuum. But: if you mean that what’s happening now is highly time-dependent, so that it doesn’t look like a c.c. to very good approximation, I’d go with 10%.
Forgive my ignorance here, but I guess I’m not sure what you’re asking with #7.
If I thought the likelihood was high that the acceleration will one day be explained in terms of some phenomenon or effect other than putting a constant in Einstein’s equation, shouldn’t I put a high percentage on #7?
Why are so many putting a low % on it?
Thanks.
Steve– because people have tried to do things other than putting a constant in Einstein’s equation, and they always make things worse rather than better. And, of course, because the constant is certainly there, the only question is what its value is (including zero).
Thanks Sean.
Hi Sean. I think I’ve heard you vehemently disagree with people who describe inflation as untested, pointing out that the theory was developed before we knew about slight deviations of n_s from 1, or that the universe was flat, etc. That, say, B-mode detection wouldn’t so much help verify inflation (because it has already passed stringent tests whose outcomes were not anticipated) as merely nail down the energy scale at which it occurred. If I’m not mischaracterizing your opinion, how can a theory be simultaneously well tested and speculative? Is it simply a question of access to the relevant energy scales in the laboratory? Because if so then we might as well all give up.
Particle phenomenologist here (faculty).
1. Inflation: 90%
2. Supersymmetry: 55%
3. String theory: 50% (Not that we’ll ever know.)
4. Some form of Higgs boson: 99% (This includes composite and pseudo-Goldstones etc.)
5. Large extra dimensions: < 1%
6. WIMP dark matter: 95% (99.99% if axions are added.)
7. Any non-cosmological-constant explanation for cosmic acceleration: no idea
Graduate student: Particle cosmology.
1. Inflation: 80%
2. Supersymmetry: 75%
3. String theory: 40%
4. Some form of Higgs boson: 90 %
5. Large extra dimensions: 20 %
6. WIMP dark matter: 75 %
7. Any non-cosmological-constant explanation for cosmic acceleration: 10%