To give a serious replyI agree. It's worse than that, too. String theory is all well and good, but it's 'background dependant', which means that if I want to be in vacuum I put that in by hand, while if I want to be near a planet i have to put *that* in by hand. That's a total deal-breaker for a theory of gravity. Ever since general relativity we've grown accustomed to theories of gravity that are 'background-independant' -- when the theory itself can determine the nature of the spacetime around it.
For me that's extremely important. Why replace something that works with something that, no disrespect meant, doesn't?
Worse than that, even, is that there are, as yet, zero testable predictions from string theory. One of the only reliable predictions a string theorist has ever made is that there are ten to the motherfucking 150 or more valid vacua. This is rather euphemistically known as the 'string landscape'. In other worlds it's known as 'having your cake and eating 10 to the fucking 150 times as much as you have'. It's no wonder string theory can reproduce (at a perturbative - ie, incomplete and unsatisfactory, level) the standard model of particle physics plus gravity, if it can also reproduce ten to the fucking 150 other universes.
Put another way, modern physics is built on symmetries. The standard model is something like U(1)xSU(2)xSO(3) or something like that; I forget. Different string theories use different groups, but the most common that I'm aware of is entertainingly known as 'heterotic' string theory - E8xE8. E8 is a group that contains U(1)xSU(2)xSO(3), and much more, inside it. So if you square the fucker of course you'll find the symmetries of the real unvierse in it. And plenty besides.
Basically, it's a theory with zero predictive power. Mathematically it's really very beautiful, and even aesthetically it's very nice - even from a physical point of view. It's a lovely idea, taking a vacuum background and having different vibrations on some strings giving us the whole of physics. But the way it's gone, it can explain anything you want it to - meaning that, beautiful maths or not, it's not physics.
At least, that's my opinion, but since i know very little more about string theory than you, it probably isn't worth all that much.
(For me that's extremely important. Why replace something that works with something that, no disrespect meant, doesn't?
Worse than that, even, is that there are, as yet, zero testable predictions from string theory. One of the only reliable predictions a string theorist has ever made is that there are ten to the motherfucking 150 or more valid vacua. This is rather euphemistically known as the 'string landscape'. In other worlds it's known as 'having your cake and eating 10 to the fucking 150 times as much as you have'. It's no wonder string theory can reproduce (at a perturbative - ie, incomplete and unsatisfactory, level) the standard model of particle physics plus gravity, if it can also reproduce ten to the fucking 150 other universes.
Put another way, modern physics is built on symmetries. The standard model is something like U(1)xSU(2)xSO(3) or something like that; I forget. Different string theories use different groups, but the most common that I'm aware of is entertainingly known as 'heterotic' string theory - E8xE8. E8 is a group that contains U(1)xSU(2)xSO(3), and much more, inside it. So if you square the fucker of course you'll find the symmetries of the real unvierse in it. And plenty besides.
Basically, it's a theory with zero predictive power. Mathematically it's really very beautiful, and even aesthetically it's very nice - even from a physical point of view. It's a lovely idea, taking a vacuum background and having different vibrations on some strings giving us the whole of physics. But the way it's gone, it can explain anything you want it to - meaning that, beautiful maths or not, it's not physics.
At least, that's my opinion, but since i know very little more about string theory than you, it probably isn't worth all that much.
boris the spider,
Fri 23 Sep 2011, 22:10,
archived)
HahaI do get the impression I'm being trolled a bit, but I like mouthing off about it because I've been mildly irritated by string theorists (and supersymmetry people) for a good few years now :)
( boris the spider,
Fri 23 Sep 2011, 22:28,
archived)
no I agreeBrian cox annoys me more though, saying the heat death of the universe is how the universe WILL end as fact, when there are so many unanswered questions.
(
Rebel biscuit stercore sumus et nos esse novimus,
Fri 23 Sep 2011, 22:42,
archived)
There are so many unanswered questionsI've spent a lot of my career looking at the assumptions of cosmology. Basically we assume
* gravity is metric
* the universe is homogeneous and isotropic on average
* the theory of gravity is general relativity
assumption (1) is more or less safe, on the scales we're working on. assumption (3) may as well be kept for the minute because we've got nothing that good to replace it with, although there are plenty of things done in cosmology to do with this. assumption (2) is simply downright wrong. firstly, "on average" is meaningless without defining an average... and we can't do that in general relativity. (well, we may finally be able to, but the jury's still currently out and in any event no work has been done on it.) secondly, while the universe "on average" may be both homogeneous and isotropic, it certainly isn't locally, or we wouldn't exist and neither would the planet, the suns, the galaxy, the local group, the local cluster or even the local supercluster. pretending that all that doesn't exist was a superb approximation for a very long time but observation is now finally catching up with theory in cosmology... and it may well be breaking down.
or it may not. that's the joy of unanswered questions. the standard model of cosmology might be totally right, as unpleasant a prospect as that seems. or it might be very wrong.
(* gravity is metric
* the universe is homogeneous and isotropic on average
* the theory of gravity is general relativity
assumption (1) is more or less safe, on the scales we're working on. assumption (3) may as well be kept for the minute because we've got nothing that good to replace it with, although there are plenty of things done in cosmology to do with this. assumption (2) is simply downright wrong. firstly, "on average" is meaningless without defining an average... and we can't do that in general relativity. (well, we may finally be able to, but the jury's still currently out and in any event no work has been done on it.) secondly, while the universe "on average" may be both homogeneous and isotropic, it certainly isn't locally, or we wouldn't exist and neither would the planet, the suns, the galaxy, the local group, the local cluster or even the local supercluster. pretending that all that doesn't exist was a superb approximation for a very long time but observation is now finally catching up with theory in cosmology... and it may well be breaking down.
or it may not. that's the joy of unanswered questions. the standard model of cosmology might be totally right, as unpleasant a prospect as that seems. or it might be very wrong.
boris the spider,
Fri 23 Sep 2011, 22:49,
archived)
I was going to ask what you think of the heat death of the universe theorywhether or not everything will just decay away and we'll be left with absolute nothingness, i mean we haven't seen a proton decay
( Rebel biscuit stercore sumus et nos esse novimus,
Fri 23 Sep 2011, 23:27,
archived)
ahathat was implicitly contained in the "standard model of the universe" bit. for that to happen, the standard model of cosmology has to be more or less accurate. (it probably is, to be honest, but there are plenty of loopholes and things that simply don't seem to make total sense.) basically the idea is that everything will end up with radiation - in the end stars will have processed almost everything that can be processed and black holes swallowed everything else and the few things left over will have decayed, and then eventually the black holes themselves will decay in hawking radiation. it seems very possible that every fundamental particle is unstable, and most if not all theories that combine the strong and electroweak forces predict that; i'm willing to believe it, to be honest, although the half-lives may be of the order of tens of billions of years, or more. given a standard cosmology, and all of that, the "heat death" seems inevitable. unless you can find a way of changing the laws of thermodynamics, and of gravity, it's hard to avoid.
except that the standard model of cosmology may be quite wrong. we may not even understand hawking radiation, although we may observe an analogue of it in the next year or two. (any quantum radiation from any kind of horizon will go a long way to justifying the argument for hawking radiation - although naturally it won't prove it. there are groups have now made acoustic black holes, which are like real black holes but for sound waves, and in a couple of years we should be in a position to measure the hawking radiation, if it exists. i'll be stunned if it doesn't.) fundamental particles may not decay. like you say, proton decay has never been observed. the universe might collapse on itself. physics we have absolutely no idea about could come into force when the universe grows too big - or if it contracts to too small a scale. the whole thing could be based on physics that is accurate on local scales but applied very badly on cosmological scales.
my view is that all bets are off in cosmology right now. at the heart of it, we don't understand what's going on - just how it looks when we interpret it using a particular model. there's a fuckload of observational support for that model, but even so... it's just a model. phenomenology, to use the jargon.
(except that the standard model of cosmology may be quite wrong. we may not even understand hawking radiation, although we may observe an analogue of it in the next year or two. (any quantum radiation from any kind of horizon will go a long way to justifying the argument for hawking radiation - although naturally it won't prove it. there are groups have now made acoustic black holes, which are like real black holes but for sound waves, and in a couple of years we should be in a position to measure the hawking radiation, if it exists. i'll be stunned if it doesn't.) fundamental particles may not decay. like you say, proton decay has never been observed. the universe might collapse on itself. physics we have absolutely no idea about could come into force when the universe grows too big - or if it contracts to too small a scale. the whole thing could be based on physics that is accurate on local scales but applied very badly on cosmological scales.
my view is that all bets are off in cosmology right now. at the heart of it, we don't understand what's going on - just how it looks when we interpret it using a particular model. there's a fuckload of observational support for that model, but even so... it's just a model. phenomenology, to use the jargon.
boris the spider,
Fri 23 Sep 2011, 23:41,
archived)
alsoin case anyone wanted MORE walls of text from me tonight (i think i'm now on a dozen ignore lists), this is where penrose's recent news stories have come from. penrose has a theory, which hasn't been satisfactorily published but which actually is quite elegant in principle, where you map the heat death of the universe onto the start of another. the details are a bit... detailed, but it boils down to looping future infinity onto past infinity, and being able to do so because the only things left in the universe are photons which for some reason i've never understood because he's not written a proper paper about this that i've ever seen means that there's no firm definitions of distance. so the massive distances at the end of the universe apparently can be mapped onto tiny distances in the very early universe. the heat death leads to a new big bang, new universes, and yet more physicists to evolve and ask WHAT THE FUCK HAPPENED TO THE ENTROPY?
oh, and also for respected physicists to work it out and then put out ill-advised papers based on statistics they readily admit they don't understand, which promptly get rubbished by the rest of the community.
(oh, and also for respected physicists to work it out and then put out ill-advised papers based on statistics they readily admit they don't understand, which promptly get rubbished by the rest of the community.
boris the spider,
Fri 23 Sep 2011, 23:47,
archived)
actually i think i'm being as clear as mudi could probably explain all this a bit more comprehensibly
( boris the spider,
Fri 23 Sep 2011, 23:49,
archived)
is that where suggested the concentric rings on the wmap image were left over gravitational waves? Rebel biscuit stercore sumus et nos esse novimus,
Fri 23 Sep 2011, 23:50,
archived)
YepThey never actually explained where the concentric rings were meant to have come from, and they used some really weird statistics where they compared everything with white noise rather than with simulated maps. That's like looking for discrepancies in a recording of a Beatles track by comparing it with white noise rather than a reasonably precise cover version. Or like looking for yellow blocks in a field of blue instead of a field of random colour. The papers were not well received - which isn't entirely Penrose's fault; he's never pretended to be an observational cosmologist nor a statistician.
( boris the spider,
Fri 23 Sep 2011, 23:54,
archived)
what if the universe is not a closed system and entropy could be leaked in?if that makes sense
i drew a horse
(i drew a horse
Rebel biscuit stercore sumus et nos esse novimus,
Fri 23 Sep 2011, 23:48,
archived)
Then all bets are off, depending on how you define "universe"For us, it basically just means "everything", so by definition entropy can't come into it from outside, and neither can heat nor anything else. What we see might just be a tiny patch of it, but what we attempt to describe is everything. (We'd term something we can't see as "superhorizon" - our metaphors are still kind of stuck in the 15th century.) Cosmology depends on superhorizon scales, but you can get some seriously interesting stuff going on if you play around. Topology is a nice example. General relativity is lovely and all, but it says *nothing* about how the world looks as a whole; it's entirely possible that's doughnut shaped, or like a football, or like any crazy shape you can imagine, perhaps like a loaf of bread that someone drilled repeated holes into. Each model can easily describe our actual universe and all our observations, but each have extremely different behaviour.
So basically if you start taking stuff outside the observational universe seriously, a lot of things can happen.
Plus, I've never been able to draw horses :( I basically can't even draw :(
(So basically if you start taking stuff outside the observational universe seriously, a lot of things can happen.
Plus, I've never been able to draw horses :( I basically can't even draw :(
boris the spider,
Fri 23 Sep 2011, 23:58,
archived)
I have enjoyed reading this.informative informed opinions.
(
arrangedletters,
Sat 24 Sep 2011, 0:13,
archived)
I would quite like to have a physicist on speedial Rebel biscuit stercore sumus et nos esse novimus,
Sat 24 Sep 2011, 0:17,
archived)
i'm not quite on speeddialbut i'm on b3ta quite a bit and normally willing to offer my opinionated opinions
edit: i also enjoy this kind of thing :)
(edit: i also enjoy this kind of thing :)
boris the spider,
Sat 24 Sep 2011, 0:19,
archived)
hah excellent can't beat a good chat about physicsEdit: i do have some questions about dark energy, but its too late
( Rebel biscuit stercore sumus et nos esse novimus,
Sat 24 Sep 2011, 0:30,
archived)