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Lubos Motl today has ranked his confidence in a whole lot of different statements about physics. I could imagine someone in the world disagreeing or agreeing with all of these statements, so it's a pretty cool list, and I find it very useful to hear what his different levels of confidence in these statements are. I wish more physicists had the balls to make their predictions as public and quantifiable like this:

Lubos Motl: Probabilities of various theories of fundamental physics

Some selected entries from his list, if you're too lazy to click:

99.999% - String theory is a mathematically consistent theory including quantum gravity, even non-perturbatively, at least in some highly supersymmetric vacua

99.995% - Black holes exist

99.99% - The Standard Model with neutrino masses is the correct description for all interactions of currently known particles in particle physics below 100 GeV with errors that can be parameterized as small corrections

99.9% - The Big Bang, an expansion of the Universe from a very small size and huge density, is a correct description of its history, at least from the age of one minute or so

99.5% - The LHC will find a Higgs boson

99% - Evaporating neutral black holes in the real world preserve information when described by the exact correct quantum mechanical model

95% - The standard model of cosmology including the cold dark matter and dark energy is correct up to small corrections - no qualitatively new large terms or concepts are necessary to explain the data

85% - String theory is the correct unifying theory, i.e. when dust is settled, it will be clear that the same equations that describe our Universe more accurately than any other theory also imply the existence of the well-known 10-dimensional and 11-dimensional vacua

50% - Supersymmetry will be found at the LHC

20% - The anthropic selection will remain the only constraint on the value of the cosmological constant that will be accessible to theorists by 2100

0.2% - The LHC will produce evaporating black holes

0.002% - A discrete model without a continuum limit is more fundamental and accurate a description of the world than any continuous model

0.002% - A model that studies quantum gravity separately from other sources and assumes that nothing beyond pure gravity exists will lead to true and valuable insights about the workings of the real world by 2100


0.001% - Doubly special relativity is a refinement of special relativity that becomes much more accurate in a wide class of phenomena

0.0005% - Basic postulates of quantum mechanics such as superposition principle and the method to obtain probabilities as squared amplitudes will be modified and the extension will describe a class of phenomena much more accurately than orthodox quantum mechanics

0.0002% - Loop quantum gravity is able to describe physics whose low-energy limit is general relativity while avoiding an infinite number of fine-tunings

0.0001% - Loop quantum gravity, with the metric as the only and well-defined degree of freedom and with quantized area, is a correct description of gravity in the real world at the Planck scale

0.00001% - One of the ESP phenomena measured in the Princeton lab actually exists and can be measured again with a similar equipment


For the most part, I think his estimates are pretty dead on. There are a few things I would move up or down, but I'm surprised at how closely I would have picked most of these numbers... even knowing much less about the details of some of them. His estimate for detecting SUSY at LHC, for instance, is 50%, which matches my publically stated estimate exactly (as captured on video in my famous bet with mauitian at Burning Man last year). The likelihood of string theory being the correct theory of quantum gravity (or at least one limit of it), I also would have picked to be around 85%. (I'm somewhat surprised that he didn't put it higher, though, as sometimes he seems to be somewhat of a string theory zealot.)

A few things that I would have adjusted up or down from his values (these are based on my own personal knowledge, not on the sum total knowledge of everyone in physics, so some of it is based on my own ignorant guesses):

1.) His statement about the Standard Model as it stands, I would revise up above the highest on the list. He originally had a stronger statement, but weakened it when someone pointed out that axions being found would negate his original statement. I think he should have added several more 9's after the decimal after he weakened it.

2.) I would adjust the "Big Bang" statement upwards. I certainly think it should be above the statement about trusting "semiclassical gravity" :) Actually, I can't imagine how this statement could be wrong... at worst, we might find there is a better way to describe it, but it's still going to be a "correct" description in at least some sense. I think I'd put it at 99.997%, just above "black holes exist".

4.) I think I'd adjust "GUT theory with unified gauge interactions" up a couple percentage points. I also might adjust "SUSY at the GUT scale or lower" up a few percentage points.

5.) "anthropic selection will remain the only constraint on the cosmological constant until at least 2100". I'm not entirely clear on what he means by this. For instance, there are things you can add to Weinberg's anthropic calculation to tighten up the bound, so you could say you added some "non anthropic" thing, but the main constraint is still anthropic. I would put it at around 99.9% that the main constraint will always be anthropic. As for whether we will add minor corrections or new constraints to that, I don't think that's a terribly interesting question, and can't really estimate a likelihood for it reliably, but his 20% chance that we will add no more constraints at all sounds as good a number as any.

6.) I think I would adjust the chances that LHC produces "stringy modes" downard at least an order of magnitude from his 0.2%, but leave the probability for producing black holes where it is.

7.) I would adjust the chances of a "discrete model" being more fundamental than a continuous model up to around 5%.

8.) Due to my ignorance of loop quantum gravity, I would not be able to put it at as low a number as him. Anything I don't know much about has to be closer to the 50% mark indicating my ignorance. So for me, I would put it at up around 0.5% (1 chance in 200, something worth it for a few people to spend time looking into) rather than the 0.0001% he puts it at. I'm willing to believe that some people have studied those types of models enough to be that confident they don't work, but until I've actually studied them myself I will give them the benefit of the doubt.

9.) I would adjust the "Princeton ESP lab" (which is misleading since it was really just one guy funding his own experiments, not anyone supported by the university... and he was a psychologist, not a physicist) downward from 0.00001% to 0.00000000000001% (1 chance in 10^16). In other words, there is no reasonable excuse in the world for a respectable university to allow crackpot ESP research to go on using their webpage and their laboratory... and I think it's irresponsible of him to compare loop quantum gravity to it by putting it only an order of magnitude away, as ESP is clearly, much, much worse. They are not at all the same level of kookiness. (Thankfully, this lab has now been closed. A few years ago, when I first heard of this, I strongly considered sending in a complaint letter saying how poorly it reflects on the university, but enough others must have done it that I didn't have to.)

[Update: sorry, I was under a bit of confusion regarding #9. The guy I was referring to in number 9 (and in the threads here) was Roger Nelson, the head of what he calls the Global Consciousness Project; apparently, this was only a spin-off of the "ESP lab" that was shut down... that presumably was what LM was referring to. I never realized these were sort of two different groups. Both working on psychic/ESP type stuff at Princeton. Here's a link about the main ESP lab being shut down (http://www.theregister.com/2007/02/13/princeton_esp_lab/). I'm not sure now whether or not the GCP was also shut down too, but I would assume/hope so.]

Comments

( 32 comments — Leave a comment )
darius
Apr. 18th, 2007 07:54 am (UTC)
All these 99s and 00s remind me of Eliezer Yudkowsky's paper on human cognitive biases where one of the phenomena emphasized was the consistent overconfidence of experts asked to give probabilities like that.

FWIW, my guesses would be closer to your figures than Mottl's.
easwaran
Apr. 18th, 2007 08:40 am (UTC)
Well, shouldn't someone investigating ESP be a psychologist rather than a physicist? They'd have much better ideas how to do controls for behavioral experiments and the like. Though if they got any significant results, they'd probably want to call in physicists and all sorts of other scientists to figure out if there's anything like a plausible mechanism.
spoonless
Apr. 18th, 2007 10:56 pm (UTC)

Well, shouldn't someone investigating ESP be a psychologist rather than a physicist?

Well, nobody should be investigating ESP, but some of the articles I read about it gave the impression that he was a physicist, which indirectly gives the impression that it's not insane from the perspective of someone who understands physics... which is a dangerous impression to give. :)

They'd have much better ideas how to do controls for behavioral experiments and the like.

This guy had no idea how to do controls or statistical analysis (see my comment to killtacular).
easwaran
Apr. 18th, 2007 11:15 pm (UTC)
It's possible now that there's already enough literature that nobody should be investigating ESP. (What about James Randi? Should he quit?) But I think that in the late 19th century it made sense for William James and others to look into these things. And there's presumably something interesting to investigate in supposed cases of out-of-body experience and sensations of ghosts and the like. It seems vanishingly unlikely that the correct explanation is that the experiences are literally true, but presumably some sort of interesting process is going on.

Of course, if that guy's research was about those random number generators "becoming less random" or whatever, then that's just crazy - it doesn't even make sense, and there's not even a phenomenon to investigate.
onhava
Apr. 19th, 2007 04:00 am (UTC)
Having read some of the work of J B Rhine, I'm pretty sure that ESP research has been pretty suspect almost from the beginning.

(I don't know what James did along these lines. Was it sensible?)
easwaran
Apr. 19th, 2007 04:42 am (UTC)
Here's a book review that discusses it. In the late 19th century, when X-rays and the like had just been discovered, I can see why people might have thought there was something to it. And of course, William James was basically the first psychologist, so his procedures clearly weren't up to modern standards. But it sounds like it was close to as sensible as one could imagine at the time.
spoonless
Apr. 19th, 2007 04:44 am (UTC)

What about James Randi? Should he quit?

I think that openly offering a million dollars to anyone who can demonstrate psychic powers is a great thing, because it helps put in perspective for the average person just how unlikely it is that anyone has such powers... and how much they would stand to benefit if they did. Other than that, I don't really see a purpose to it.

I assume that this is implied, but in case anyone reading this takes me the wrong way... I should put a disclaimer that I have no problem with anyone investigating this kind of stuff on their own time. I just don't think it is worthy of being sanctioned by, funded by, or associated with, an actual university. Mixing pseudoscience with real science is a bad idea, because after a while people would associate the failings of the former with the latter, and stop trusting science altogether.
island01
Apr. 18th, 2007 09:29 am (UTC)
Hi Jeff, are you a string theorist?

I strongly agree with your statement:

I wish more physicists had the balls to make their predictions as public and quantifiable like this:

Unfortunately, Lumo's confidence is also unshakable, and he has a very strong tendency to deny and censor any information that he doesn't like, and regardless of merrit.

I've known him for a number of years now, and the only time that I ever got him to admit that he was wrong about anything was when I corrected him in the moderated research forum and he had no control over it.

But I've lost all respect for him since.

Anyway, sorry to barge-in un-invited, but I found you via a key word search.

Maybe Lubos thinks that god is coming in the year, 2100?.. ;)

spoonless
Apr. 18th, 2007 06:14 pm (UTC)

Hi Jeff, are you a string theorist?

I'm just a graduate student, but my advisor is a string theorist (actually, he was also Lubos's advisor). I've learned enough about strings to think string theory "looks very promising" but I have not published any work myself on string theory (my current work revolves around constructing a particular GUT that is compatible with certain TeV-scale assumptions). So like I say, a lot of my levels of confidence should be taken with a grain of salt since I'm less familiar with a lot of these things than actual people who have been working in the field for a while. It does look like the next project I work on will more directly relate to string theory, but the truth is, it's hard to say where the boundry between strings and particle physics is any more... everything is interconnected.
island01
Apr. 18th, 2007 07:59 pm (UTC)
I've learned enough about strings to think string theory "looks very promising"

heheh... it's looks like you've learned a liitle bit about safe-politics, as well.

And I hope that it works out for you, because you don't appear to be good enough with money to get a job on wallstreet if the colliders don't find anything... ;)
spoonless
Apr. 18th, 2007 11:10 pm (UTC)

because you don't appear to be good enough with money to get a job on wallstreet if the colliders don't find anything... ;)

heh... at least I got the right order of magnitude (if this is referring to my $9/$10 slip.)
island01
Apr. 19th, 2007 01:25 am (UTC)
Yeah, I was only teasing you.
firmament
Apr. 18th, 2007 10:39 am (UTC)
Pffft. The part of this that is "quantifiable" is pretty bullshit quantities, IMHO. I don´t think it makes a lot of sense to assign subjective credence in numerical form. Maybe you can give ordinal credences, but I don´t know that assigning pure numbers makes sense.
spoonless
Apr. 18th, 2007 06:00 pm (UTC)
I agree that beliefs are usually more complicated than just 1-dimensional numbers on a scale. (For instance, there are usually a lot of ways in which things can be "kind of wrong" about something and it's not clear whether to count it as wrong or right.) But I think the clearer the statements you make, the easier it is to assign actual numbers to them. Most of these are pretty clear statements, although there are a few such as the one about the anthropic prinicple and the one about the big bang that I feel are not clear statements... so I just sort of averaged the different interpretions I could think of for them to the best of my ability.

I think percentages do make sense if the statements are clear enough. The way I think of it is, out of the billions of beliefs I have had over the course of my life, does the strength of my conviction for this particular statement compare to the type of belief that has turned out wrong 1 in 10 times, 1 in 100 times, or 1 in 1000?, etc. You could also think of it as a question about how I would act if I were offered a bet on it. If I'm 90% sure of something, then that means I'm willing to match $10 for every $1 that someone puts up to me in a bet (minus a fee for the effort of thinking about it, risk, hidden costs, etc.) up to the point where it starts to get up to values I couldn't afford to risk.

So yes, there are problems with assinging numbers to subjective confidence levels, but a.) it's fun, and b.) it does have some validity, and c.) it's useful to know where other people stand on things compared to other things, rather than trying to sift through the various statements they've made in the past and guess.
spoonless
Apr. 18th, 2007 06:22 pm (UTC)

I'm 90% sure of something, then that means I'm willing to match $10 for every $1 that someone puts up to me in a bet

oops, I mean $9 of course :)
easwaran
Apr. 18th, 2007 11:11 pm (UTC)
The betting interpretation is the best way to make sense of it that I know. If the betting behavior is right, then the numbers have to satisfy the probability axioms, or else you're vulnerable to "dutch books", where you'll accept a series of bets individually that guarantee you lose money overall.

I think the strongest challenges point out that people don't buy and sell bets at the same price. The natural way to deal with these cases then suggests that people don't have a single probability function but rather a whole set of them. You can talk about the ranges of values assigned to particular propositions, but you lose some information about independence and correlations and the like if you don't consider the complete probability functions.
killtacular
Apr. 18th, 2007 09:11 pm (UTC)
Very interesting, and also illuminating to non-physicists :).

"95% - The standard model of cosmology including the cold dark matter and dark energy is correct up to small corrections - no qualitatively new large terms or concepts are necessary to explain the data"

Why would you mostly agree with this? It seems that y'all have no good description of what "cold dark matter" and "dark energy" is, right? And yet, they appear to play pretty significant roles in the universe. If we can't describe them now using our current conceptual framework, might it be somewhat likely that new concepts will come into play to so describe them and why they are, at least right now, mysterious? So 95% might be too high? I dunno, I don't really understand much of it.

And, ESP like extra-sensory perception, or ESP meaning something else in physics?
spoonless
Apr. 18th, 2007 10:49 pm (UTC)

It seems that y'all have no good description of what "cold dark matter" and "dark energy" is, right?

For dark matter, it's just an issue of identifying which high energy particles contribute to it, and what exactly their masses are. We have a whole zoo of different candidates, so one of them or several of them, or even all of them could be what comprises the dark matter. None of them require any fundamental changes to our current model. I think in some ways, the media may have misled people into thinking dark matter is more mysterious than it really is. It's actually necessary for things like galaxy formation, so if we hadn't seen dark matter there would have been huge problems with the current models. It shows up quite naturally in many models of low-energy supersymmetry which is something string theorists were expecting anyway. I would say if anything, it's confirmation that our current theories are on the right track.

For dark energy, pretty much everyone agrees that it is either vacuum energy, or vacuum energy plus a cosmological constant, which are both effectively the same thing. There are two main unanswered questions about dark energy. One of them is whether it has changed over the course of the universe or remained constant. And the other is why the current value we're measuring is so incredibly tiny (about 10^-120 in "natural units"). The second of these is often called "deep and mysterious" and there are many people who have suggested radical things such as large-distance modifications of gravity to account for it. However, I'm pretty confident that I already know the answer to why it's so small: the correct answer is the anthropic principle. I think Lubos Motl is more skeptical of this, but I would put that up there at 99.9%.

At any rate, both dark matter and dark energy fit in very well to our current models, so unless there are big unexpected surprises coming, there is no good reason to expect the current ideas will need to be modified. In contrast, something like MOND (an alternative to dark matter that has since been ruled out as a possible explanation for it) if it had been true would have completely overturned our current models of physics, and been shocking to nearly everyone... and would have required a whole lot of new bizarre concepts.

Anyway, I would agree with the 95%.

And, ESP like extra-sensory perception, or ESP meaning something else in physics?

ESP meaning extra-sensory perception. In particular the guy claimed to have set up a random number generator that suddenly got "less random" during September 11th due to all of the bad vibes coming from New York and all over the world. Unfortunately, the media made it sound like this guy was actually a physicist at Princeton, when in fact he was a crazy psychologist with a BS in physics who had conducted his own experiments with private funding and set up his webpage using Princeton's servers. Looking at his data, he had a severe lack of understanding for statistics... not to mention, the craziness of his ideas. Unsurprisingly, they finally shut him down and told him to leave, even though he never admitted that his data was complete bullshit.
killtacular
Apr. 19th, 2007 05:50 am (UTC)
For dark matter, it's just an issue of identifying which high energy particles contribute to it, and what exactly their masses are. We have a whole zoo of different candidates, so one of them or several of them, or even all of them could be what comprises the dark matter

Sure, but couldn't whatever particles do make up dark matter be ones that aren't in the standard model of QM? I mean, without actually observing and testing some actual dark matter you can't be all that sure that it is actually made up of particles in the standard model, right? Or am I missing something? If it is just that our cosmological theory predicts cold dark matter of some type, and we in fact see that there is, couldn't it be made up of some new type of extra-standard-model particles? That would seem to require new concepts. If that is actually the case, I would put the confidence in it at a lower level.

It shows up quite naturally in many models of low-energy supersymmetry which is something string theorists were expecting anyway. I would say if anything, it's confirmation that our current theories are on the right track.

I mean, I certainly don't know much about what is going on. Do those models predict dark matter of a specific kind, ie, a range of already-believed-to-exist particles? And do we have reason to think that just those models of low-energy supersymmetry by themselves predict the correct abundance of dark matter?

However, I'm pretty confident that I already know the answer to why it's so small: the correct answer is the anthropic principle

I dunno, while appeals to the anthropic principle certainly are legitimate, I think they can also serve to cut off debate : ie, there is no antecedent reason for x, but if not-x then we wouldn't be here, and we are here, so x. That is an explanation, but there certainly always could be another one. Why, exactly, should we have reason to believe that there is vacuum energy or a cosmological constant? I had always thought we should be unhappy with just positing another basic constant (the problem with the standard model in QM is that it has way too many of these - 18? - right?)

At any rate, both dark matter and dark energy fit in very well to our current models, so unless there are big unexpected surprises coming, there is no good reason to expect the current ideas will need to be modified

I guess my point was the fact that they do fit with our models isn't good enough to give 95% confidence that our models are, by themelves, sufficient. While we shouldn't worry that we might have to modify our current ideas we might have to supplement them. I guess my worry is that the standard model might be incomplete, and given that we haven't been able to investigate dark matter (specifically, dark energy might be fine) we don't really know that it is composed of particles already accounted for in the standard model. But, again, I'm no physicist and, as you point out, the science media is often fantastically wrong.

ESP meaning extra-sensory perception. In particular the guy claimed to have set up a random number generator that suddenly got "less random" during September 11th due to all of the bad vibes coming from New York and all over the world.

Ahh, ya, I read about that a bit ago. I didn't know he had the princeton connection, however. That is total bullshit, and doesn't really make any sense.
spoonless
Apr. 19th, 2007 08:55 am (UTC)

And do we have reason to think that just those models of low-energy supersymmetry by themselves predict the correct abundance of dark matter?

They are exactly the right type of particle that would produce the effects we see, but no... unfortuantely, there is no way to predict accurately what the abundence would be without measuring it. That would of course be more convincing :) To get a better idea of whether it is indeed supersymmetry, or something else, we just have to wait and see what turns up at LHC. It's just one possibility of many, albeit the most popular possibility.

and given that we haven't been able to investigate dark matter

This is not true. We've been investigating it from all sorts of different experiments, coming at it from lots of different angles. There is a lot of dark matter data, some from galaxies, some from the cosmic background radiation, some from direct dark matter detector experiments. All of these have been making good progress on narrowing down the possibilities. We have a much better idea today what exactly the dark matter is than we did 10 or even 5 years ago.

while appeals to the anthropic principle certainly are legitimate, I think they can also serve to cut off debate

A correct answer always cuts off a debate... but that's not necessarily a bad thing. When you find out the answer, you stop looking. For example, if someone's parents get killed in a car wreck, they might spend the whole rest of their lives trying to figure out "why, oh why did this happen to me and my family!" but the truth is, it didn't happen for a reason, car accidents just happen. So the longer they search for an answer there, the more of a fool they are going to be. Equally important to knowing when you should stay in the game, it's good to know when you've already got the answer and should quit. And in my opinion, this is just such a case. I'm not saying it's such a waste of time that nobody should do it... I'm just saying that I personally would not waste my time on it because I already believe we have the answer.

the problem with the standard model in QM is that it has way too many of these - 18? - right?

Well, I am certain there are a lot more constants out there than the 20-something in the Standard Model. So I would not say that's the "problem" with the Standard Model. The Standard Model is only a small piece of the world... the rest will require more constants to describe. String theory has zero constants in it, it's all determined by pure geometry, so if string theory is right then all of these "constants" are just environmental conditions nearby us. So in effect... I guess I'm saying that yes, eventually we will hopefully reduce the number of constants, but we are certainly not to that point yet... before we do that, the number must go up. The cosmological constant is just one of many that will need to be added.
killtacular
Apr. 20th, 2007 04:30 pm (UTC)
some from direct dark matter detector experiments.

ahh, cool, this was what I was talking about and I (mistakenly) thought we hadn't been able to do anything like this. If we can directly detect dark matter in the lab, then that is pretty sweet (and good to know that I was wrong)!

A correct answer always cuts off a debate... but that's not necessarily a bad thing.

Right, but you can put your car crash example a different way. You can ask "why did this happen" as "what was the reason this happened to you." In that case, there is no answer. You could also take it as "why did this happen rather than not happen." In that case, you could say that their parents got hit by a drunk drive, or the car malfunctioned, or something like that. I think when talking about fundamental physical constants we should sometimes ask the latter type of question, especially if string theory is ultimately going to be the best theory we have for a while (or any theory that doesn't have any, or many, fundamental physical constants). Does that make sense?
spoonless
Apr. 20th, 2007 06:26 pm (UTC)

If we can directly detect dark matter in the lab, then that is pretty sweet (and good to know that I was wrong)!

Actually, the "direct detection" experiments I was referring to have not detected any dark matter. What they've done is tell us more about what the dark matter is by not detecting any. It places important constraints on the parameters involved in describing the dark matter, and narrows down the possibilities for what it is. They could detect it any day, but so far they have not. At any rate, it's still true that they are investigating it in this manor.

The closest to actual direct detection they've come (which is close enough for most practical purposes) is the collision between two galaxies observed with NASA's Chandra telescope. Most media sources reported this as Direct Proof of Dark Matter, which is also what NASA referred to it as in their press release, although I think this is a slight exaggeration (I would not use the term "proof" even though it was one of the two final blows that came within the past couple years for non-dark-matter-based theories.)
spoonless
Apr. 20th, 2007 07:58 pm (UTC)
To give you a better idea of the wealth of data that has been generated by "direct detection experiments", check out this webpage which attempts to combine it all together and let you plot all the different constraints:

http://dendera.berkeley.edu/plotter/entryform.html

The direct detection experiemnts I hear about the most are the CDMS (Cryogenic Dark Matter Search) experiments; here's a webpage describing how they work:
http://cdms.berkeley.edu/experiment.html

I meant to add, that there are really two reasons why I would not have used the word "direct proof" for NASA's observation. One, because I don't think the word proof should be used regarding empirical observations. And two, because the phrase "direct detection" is usually reserved for actually detecting the dark matter that exists here on earth (which is what CDMS looks for), rather than measuring the effects of dark matter in distant galaxies or in the cosmic background radiation.
spoonless
Apr. 21st, 2007 06:07 pm (UTC)

You could also take it as "why did this happen rather than not happen." In that case, you could say that their parents got hit by a drunk drive, or the car malfunctioned, or something like that.

Right, this is the way I was intending the question. And yes, that would be the correct answer. But my point is, it's the only answer you can give, whereas a lot of people would go on and say "well, I still feel there is something more mysterious about it... there must be some deeper reason why it happened" and they would be foolish to think so. This is exactly analogous to the cosmological situation. Some of us firmly believe that we've already found the only answer and others say "come on... you've got to be kidding, there must be some other explanation!" And the rest of us just say "nope, sorry, that's the only explanation there is." Statistically, the odds that there is another answer are astronomically against. You would have to believe in a huge cosmic conspiracy to believe that there is another answer... not something I'm willing to entertain.
spoonless
Apr. 21st, 2007 06:11 pm (UTC)

Statistically, the odds that there is another answer are astronomically against. You would have to believe in a huge cosmic conspiracy to believe that there is another answer... not something I'm willing to entertain.

This is, of course, assuming that there's not some weird thing that we're missing that changes the nature of the whole thing. That's the only reason I put the confidence down at 99.9% rather than up at 1-10^-118, which is what it would be if you literally look at the statistics and trust our current knowledge of physics.
spoonless
Apr. 19th, 2007 04:19 am (UTC)
a couple more comments on dark matter
It might also be worth mentioning that when he says "The Standard Model of Cosmology including Cold Dark Matter and Dark Energy", that's redundant. The phrase "Standard Model of Cosmology" is something that refers to the consensus that has formed within the past 5 years or so, that the energy in the universe is primarily dark energy, with some cold dark matter, and a tiny bit of regular matter. These percentages have been measured fairly accurately, and all of the data fits and looks very nice... it's perhaps the first time in history we've had such a nice model of cosmology, with no big missing holes or pieces. So as I mentioned in the previous comment, the main task left is finding which particles compose the dark matter... however, that answer will not really affect the cosmology. Or if it does, only very slightly... since the thing that matters in cosmology is the mass/energy density, not the details of how the particles making up the mass behave.
killtacular
Apr. 19th, 2007 05:58 am (UTC)
Re: a couple more comments on dark matter
Does it follow from how we think the big bang was and the laws of physics that the universe is mostly dark energy, with some cold dark matter and a tiny bit of regular matter? Or, is that what we observe, so that makes up what the standard model of cosmology is? The direction-of-fit is what concerns me, I guess.

In any case, I wouldn't be worried that what actually makes up the dark matter should affect our cosmology, especially if it already nicely takes account for the presence and amount of dark matter out there. I would rather be worried with the claim that we don't need to add any new concepts/particles/stuff to our theory : couldn't there be entirely novel types of matter that make up dark matter, but has the effects required for the observations we have? Without being able to actually observe dark matter, I can't see how this possibility can be eliminated, or even really doubted (because the standard model isn't taken to really be complete. The confidence given above in the standard model is for currently known particles, how do we know that the particles that make up dark matter are themselves some or other of our known particles?
spoonless
Apr. 19th, 2007 08:30 am (UTC)
two different Standard Models

Or, is that what we observe, so that makes up what the standard model of cosmology is?

It comes from a combination of a number of independant observations, all of which fit nicely together and mutually reinforce each other.

I wouldn't be worried that what actually makes up the dark matter should affect our cosmology [...] I would rather be worried with the claim that we don't need to add any new concepts/particles/stuff to our theory

Well, then you would be rightfully worried! However, that wasn't the claim made in the statement. The statement was that the Standard Model of Cosmology is correct... this is a model of cosmology, not of particle physics. The Standard Model of Particle Physics is completely different, and yes... new things will most definitely need to be added to it. Not just because of the dark matter, but because of all sorts of things. The Standard Model is only intended to be a theory of physics up to 100GeV or so. Above that, nobody knows what lurks... there are many theories, but until somebody turns on the LHC or another accelerator, there is no way to know for sure what is there. I'm
currently working on a theory which involves things called pentaquarks. Other stuff (besides Higgs bosons) that may be there include supersymmetry particles, technicolor, compositeness, Z' bosons, black holes, and of course dark matter (which is probably already included in the list). Or there could be stuff there that nobody has guessed. But none of that goes against any of the statements made on the list.

So I think the confusion here was... yes, everyone expects the Standard Model of Particle Physics to be extended to include new particles, for many different reasons. But the statement was referring to the Standard Model of Cosmology... a different beast entirely.
killtacular
Apr. 20th, 2007 04:32 pm (UTC)
Re: two different Standard Models
ahhhh, ya, I was confused, and that cleared it up (as well as addressing my general type of worry along the way). Sweet, thanks! :)
island01
Apr. 19th, 2007 01:29 am (UTC)
the correct answer is the anthropic principle, but I would put that up there at 99.9%.

Yeah, because it's just an energy conservation law.
island01
Apr. 19th, 2007 09:26 am (UTC)
There is no standard model of cosmology yet.

There IS a most conservative mainstream approach, which looks nothing like what's been assumed here.

And there is a model that cutting-edge theorists most like, which is wrongly being assumed to be the non-existent "standard model".
spoonless
Apr. 21st, 2007 02:41 am (UTC)
The term "Standard Model of Cosmology" is fairly new, and obviously doesn't have the long history of use that "Standard Model of Particle Physics" does (and is on nowhere near as firm a footing). But I do think it's starting to gain acceptence... at least some people are using that term. I suppose calling it Lambda-CDM would be better, in case it turns out the story is more complicated.

What do you mean by the statement that there are more "conservative" approaches? Lambda-CDM is the most conservative that fits all the data (for just about any sense of "conservative" I can imagine). Anything else is a bit of a long shot/speculation.
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