While we’re getting the multiverse out of our system, let me point to this interview with Leonard Susskind by Amanda Gefter over at New Scientist (also noted at Not Even Wrong). I’ve talked with Amanda before, about testing general relativity among other things, and she was nice enough to forward the introduction to the interview, which appears in the print edition but was omitted online.
Ever since Albert Einstein wondered whether the world might have been different, physicists have been searching for a “theory of everything” to explain why the universe is exactly the way it is. But one of today’s leading candidates, string theory, is in trouble. A growing number of physicists claim it is ill-defined, based on crude assumptions and hasn’t got us any closer to a theory of everything. Something fundamental is missing, they say (see New Scientist, 10 December, p 5).
The main complaint is that rather than describing one universe, the theory describes some 10500, each with different kinds of particles, different constants of nature, even different laws of physics. But physicist Leonard Susskind, who invented string theory, sees this huge “landscape” of universes not as a problem, but as a solution.
If all these universes actually exist, forming a huge “multiverse,” then maybe physicists can explain the way things are after all. According to Susskind, the existence of a multiverse could answer the most perplexing question in physics: why the value of the cosmological constant, which describes how rapidly the expansion of the universe is accelerating, appears improbably fine-tuned to allow life to exist. A little bigger and the universe would have expanded too fast for galaxies to form; a little smaller and it would have collapsed into a black hole. With an infinite number of universes, says Susskind, there is bound to be one with a cosmological constant like ours.
The idea is controversial, because it changes how physics is done, and it means that the basic features of our universe are just a random luck of the draw. He explains to Amanda Gefter why he’s defending it, and why it’s a possibility we simply can’t ignore.
“While we’re getting the multiverse out of our system…”
Lines you never expected to hear from a Respectable Physicist, #314159.
Michael Moorcock has a lot to answer for.
The idea is controversial, because it changes how physics is done
Only if you let it.
Sorry, but the multiverse concept does sound little too close to a “magic” solution to me.
1)It plays off the sci-fi disposition that such a thing would favorable (like people wanting an afterlife). It is always advisable to be cautious of the giving idea more credibilty because we want them to be real.
2)It seems to address a key hole with bulldozer. Ackham’s Razor, anyone?
Hahaha! It’s really quite amusing to watch string theory self-destruct 😉
I’ll see you in another dimension, Mother:)
Weren’t you looking for a TOE? Now you’ve got a TOEE (Theory of Every Everthing)!
“Don’t worry, be happy…”
Susskind invented String theory?
I’m quite ignorant about this, what was his role in early String theory?
fh, go to
http://www.edge.org/3rd_culture/susskind03/susskind_index.html
and search for the first occurrence of the name “Veneziano”. That’s where the story begins.
As a layman (I’m not a professional physicist) I find all this talking about multiple universes extremely depressing and senseless.
Is it a wonder to anyone that in last decades not one phycisist working in high energy physics/super string theory has been awared the nobel prize ?
Where are the new generation of Feynmans, Einsteins, Diracs, Schwingers, Fermis, Bohrs etc, etc, etc….
Superstring Theory is every day disconnecting itself more and more from physics and is becoming something else.
I don’t know what but it surely isn’t physics.
Ugo, the Nobel prize doesn’t go to “pure” theory – experimental confirmation is required. That pretty much rules out string theory. But HEP has been a dominating theme of the last few decades:
http://nobelprize.org/physics/laureates/1979/index.html
http://nobelprize.org/physics/laureates/1982/index.html
http://nobelprize.org/physics/laureates/1984/index.html
http://nobelprize.org/physics/laureates/1988/index.html
http://nobelprize.org/physics/laureates/1990/index.html
http://nobelprize.org/physics/laureates/1992/index.html
http://nobelprize.org/physics/laureates/1995/index.html
http://nobelprize.org/physics/laureates/1999/index.html
http://nobelprize.org/physics/laureates/2004/index.html
Dissident said :
I know this, what I’m trying to say is that in the past a lot of theoretical physicists working on high energy physics received the nobel prize because they created a theory to explain experimental data.
Theoretical physics should work this way, there is a symbiosis between experiemental data and trying to devise explanations for those data.
Now don’t you find it kind of weird (in a depressing sort of way) to see that not one nobel prize has been given to theoretical physicsts working on string theory, string theory effectively dominating the high energy physics landscape. (no pun intended).
I mean, from my point of view I would like string theory to be ridimensioned within the theoretical physics community.
It is unbelivable that young researchers to have a career in theoretical physics have only one option : do string theory.
This is something fundamentally wrong.
Alas, the situation of the last couple of decades has been total absence of new experimental data to explain; the standard model has passed every test thrown at it (latest ray of hope is the anomalous magnetic moment of the muon, which just might hint at substructure, but not yet with sufficient certainty). So theorists have been on a prolonged vacation of sorts, engaging in flights of fancy rather than in the scrutiny of puzzling experimental data. Strings are the most notorious result – and no, I don’t find it weird that they haven’t been recognized with a Nobel prize, since that would require connection with experiment.
But the redimensioning you ask for is looming. Strings have been getting some pretty bad press lately, and if the LHC fails to come up with sparticles in the next few years, anything with the prefix “super” in its name will start looking pretty dated even to the believers. But then the question is what you’re going to get instead. Just another flight of fancy afflicted by the same problems of practical (if not fundamental) lack of falsifiability? Or perhaps just an exodus to other fields, like biophysics, where there’s real work to do?
An added source of confusion regarding the landscape is the word “Multiverse”.
In this context Susskind and others have given it a meaning that differs from its meaning in quantum information theory, where the word was first introduced into physics.
Susskind himself is confused about this, as evidenced by his remarks from the audience during the panel discussion at Strings 2005 last summer.
New Scientist: The idea is controversial, because it changes how physics is done
Aaron Bergman: Only if you let it.
Hear, Hear! That’s the spirit!
What’s annoying about all of this is that, even if true, the cosmological constant would not be — as is often pointed out by the anthropicists — the first time that some parameter was decided to be anthropically determined. The distance from the earth to the sun is a classic example.
So, when it was realized that this parameter was probably just random, did people all of a sudden start declaring that there was a new way to do science? Did they start using the theory of planetary formation to come up with a probability distribution for the planetary distances? In this case, there clearly is a ‘multiverse’. We see tons of other galaxies, lots of stars and even a few planets out there. Has anyone bothered trying to probabilistically ‘predict’ the distance from the earth to the sun using some not particularly well formulated principle of mediocrity?
Of course not. It might be a fun game, but it’s not particularly interesting. We already know what the distance from the earth to the sun is. There was no reason to elevate such games to a fundamental goal of science. Nobody was out proselytizing that “revolution” as far as I know. They just went on to try to understand things that weren’t random.
I wish people these days would do the same.
Here is where I think that the analogy between fundamental physics and planetary distance breaks down: We see tons of galaxies, and expect there to be tons of planets, and they are all different. We also see tons of electrons, and they are all the same; as far as we know, the mass, charge and spin of all electrons in the universe are identical. If the electron mass (or spin!) were determined anthropically, we would expect it to vary throughout the universe, and there should be ways to detect that variation. If a planet’s distance from its sun were determined anthropically, we should analogously be able to see planets at different distances. And we do!
Susskind makes the analogy with the fiords in Norway. But all fiords in Norway are different, and they are certainly different from the fiords at CERN (since there aren’t any). But all electrons in Norway look the same as all electrons at CERN!
aaron bergman, that is the precise point. To this moment I don’t understand how the anthropic principle is different or superior to “meassuring things”. In fact abstractly you canphrase it that way: We meassure that humans exist, what can we deducae from that? It sounds unlikely that that would ever produce a better result then meassuring things directly.
Ugo wrote:
It is unbelivable that young researchers to have a career in theoretical physics have only one option : do string theory.
This is something fundamentally wrong.
This simply isn’t true. Aside from theoretical condensed matter, theoretical astrophysics, and other parts of physics, this isn’t even true in high-energy physics. There’s a great deal of phenomenological research.
Aron, please don’t re-define the anthropic principle for string theorists by generalizing them as anthropicists. String theorists did not originate, nor does their lame interpretation “own” the anthropic prinicple. Quite to the contrary, their interpretation cannot take precedence over the implications for specialness in the one observed universe, unless and if it ever enables them to predict anything more accurately than a single universe interpretation of the anthropic principle allows for.
The anthropic principle is a cold hard fact of the observed universe whose significance cannot be lost in multiverse “reasoning” unless you can prove that you have good reason to do so.
Call them crackpot multiverse string theorists like everybody else does, but please do not confuse them with normal people who know that anthropically determined means that there can no accident to it.
Thanks
Thomas Larsson (#16),
Well, not all possible universes can be equally likely. I’m assuming that you are considering some sort of set of all possible universes and are applying anthropic reasoning to that set.
There are a huge number more complex models with zillions of arbitrary constants that look like the standard model at low energies. The effect of those parameters would be small, e.g. tiny fluctuations in the electron mass that are measurable but yet doesn’t affect chemistry.
Because everything indicates that the world is as simple as possible, and not as complex as possible at the fundamental level, there must exist a measure that favors less complex models.
If one identifies universes with algorithms, then it’s easy to see where this measure comes from. You can always add n bits to a program that don’t affect the program. There are 2^n times more universes with n dummy bits added on. So, if the measure depends only on the number of bits needed to specify the program (Kolmogorov Complexity), then it has to fall off faster than 2^(- program length) to cancel out the exponentially growing anthropic factor.
When I first went on the job market, that’s exactly how it seemed to me: string theory or no job. I remember as job candidate lamely attempting to put a string theory spin on my quantum gravity work that actually had nothing to do with string theory. I believe that I was offered a position primarily on the strength of social connections (between my advisor & recommenders and the group that hired me).
For the most part, jobs are available only to those who are keenly career conscious (or lucky). You really need to think about the job market, when you’re a senior applying to graduate school. At the very least you need to be thinking about it, when you’re a first-year graduate student choosing a specialty. It’s not a bad idea, moreover, to consciously cultivate future references.
The problem is that lots of bright people focus on physics instead of on a career in physics. The most famous example of this is Albert Einstein, who was academically unemployable after he received his degree. If he hadn’t, on the strength of a social connection, landed a low-stress, leisure-providing job in the Swiss patent office, I shudder to think what might not have happened.
Aaron– I completely agree that the “new paradigm for physics” business is just silly. The whole point is that we have always done physics this way — some features of nature are deep and inevitable, and others are contingent and environmental. The reason why respectable scientists should spend time thinking about the multiverse is that we would really like to know whether the vacuum energy is the former or the latter. Right now we don’t know why there is such a large hierarchy between the vacuum scale and the Planck scale; maybe there’s some inevitable dynamical mechanism, maybe it’s just a selection effect. The underlying understanding is completely different in the two cases, so it’s important to understand the feasibility of each scenario.
The reason why respectable scientists should spend time thinking about the multiverse is that we would really like to know whether the vacuum energy is the former or the latter.
I’m just not sure that question’s is going to be answerable any time soon. The odds of observing another universe are pretty slim. I suppose we could get a ton of other evidence for some theory that predicts zillions of universe, but that seems pretty unlikely these days, too.
In the meantime, it seems to me we ought to be trying to best understand the theory’s we have, multiversal or not, and if people want to think about the cosmological constant, that’s cool, and if they don’t, that’s cool too.
No need for revolutions, new paradigms or whatever. Just physics. Like we’ve always done it.
Sean and Aaron, I like separating anthropic resoning (like Hoyle’s) and the issues involved, from probabilistic reasoning and the completely different issues involved there. The former is conventional physics, and the upshot would be that the CC is a coincidence like the earth-sun distance, and therefore it is not interesting for scientific study. The latter, using conditional probabilities to actually give value to the CC, or the earth-sun distance, is a very different approach. If it is ever going to make sense, it would indeed be a new way of doing physics, paradigm shift etc. etc..
The introduction to the interview says Susskind “invented string theory.”
This canard can be found on the front flap of Susskind’s book and is
repeated in various forms in many reviews of the book and interviews
with Susskind. An early review of string theory (C. Rebbi, Physics Reports
12 C, no. 1, 1974) says “The first interpretation of the spectrum of states of the conventional dual resonance model as the spectrum of excitations of a one-dimensional system (a string) is due to Nambu[23], Nielsen[24],
Susskind[25], and Takabayashi[26]. I believe the references are listed
in chronological order. Readers who want to get the history straight
are invited to look up the references and decide for themselves.
My conclusion is that Susskind was among the
first people to interpret the Veneziano model in terms of what we now call
strings, but definitely not *the* first. How this makes him the father of
string theory or the inventor of string theory is beyond me.