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from the unterminated-strings-cause-inflation dept.
Submitted via IRC for SoyCow1984
Our universe: An expanding bubble in an extra dimension
According to string theory, all matter consists of tiny, vibrating "stringlike" entities. The theory also requires there to be more spatial dimensions than the three that are already part of everyday knowledge. For 15 years, there have been models in string theory that have been thought to give rise to dark energy. However, these have come in for increasingly harsh criticism, and several researchers are now asserting that none of the models proposed to date are workable.
In their article, the scientists propose a new model with dark energy and our Universe riding on an expanding bubble in an extra dimension. The whole Universe is accommodated on the edge of this expanding bubble. All existing matter in the Universe corresponds to the ends of strings that extend out into the extra dimension. The researchers also show that expanding bubbles of this kind can come into existence within the framework of string theory. It is conceivable that there are more bubbles than ours, corresponding to other universes.
Journal Reference:
Souvik Banerjee, Ulf Danielsson, Giuseppe Dibitetto, Suvendu Giri, Marjorie Schillo. Emergent de Sitter Cosmology from Decaying Anti–de Sitter Space. Physical Review Letters, 2018; 121 (26) DOI: 10.1103/PhysRevLett.121.261301
(Score: 5, Informative) by johnlongjohnson on Sunday December 30 2018, @08:44PM (13 children)
I keep seeing so many replies along the lines of "I don't understand it, it must be false" or "string theory is only for grant money" or "where's these supposed extra dimensions" and bunch of other general anti-science viewpoints.
If you don't understand something admit it and ask for help. Don't sit and denigrate it. You guys sound like climate deniers. You're making the same claims and based on even weaker arguments than the anti-vax and climate deniers.
Every theory we have is incomplete period. There is no theory we have which predicts all we see.
The best theories we have, still miss important things like gravity.
This doesn't mean that they are wrong.
It just means there's more between heaven and earth than we comprehend at the moment.
Yet all these advances in theory eventually shake out to something.
115 years ago we couldn't explain why striking a metal plate with a light produced a voltage at all.
Then once we figured out why we still couldn't explain why varying the intensity of the light didn't change the voltage.
Eventually we realized that light was in fact a quantized excitation of the electromagnetic field and because it was quantized, the frequency i.e. color of the light determined the voltage while the intensity of light determined the number of electrons being moved, i.e. the amperage.
To get from Maxwell's theories to Einstein's theory of corpuscular light took > 70 years
We got lucky with Einstein because not only did he essentially invent quantum mechanics, he also gave us relativity.
Now we have a problem. Relativity does a great job explaining gravity. Quantum Field Theory does a great job explaining everything else, but gravity is a square peg in a round hole.
Enter Feynman who managed to come up with a relativistic solution to Schrodinger and Kaluza & Klein who realized that extending gravity to 5 dimensions produces a force cogent to gravity that happens to match Maxwells equations for electromagnetism and you have double trouble. Can we keep extending relativity into multiple extant dimensions in hopes we find the other forces, dimensions by which by all accounts we can't see or feel, or do we look for a way to try and get gravity to play nice with the other forces?
It literally took until 2018 before we could falsify Kaluza Klein. EM and Gravity come to us through the same number of dimensions. Gravity isn't leaking in from higher dimensions, at least not dimensions which are macroscopic. Thus the only way to persue KK theory while maintaining intellectual honesty is to assume compact dimensions.
But this has been known for a long time because Kaluza himself proposed it way back when.
In fact it was Kaluza's idea that every point in space and time must have 1 extra spatial dimension, a dimension which is compact and curled onto itself. Sound familiar?
String theory is not some new theory that came out of the blue. It is the natural evolution of what we already had. Interestingly enough, one thing that keeps shaking out in string theory and the thing that makes it so fascinating is that predicts gravity. In fact it's really, really hard to have string theory which doesn't immediately start pumping out gravitons.
This tells us something about string theory or as it's called now M theory.
Gravity comes to us in almost all formulations of the theory. This means that simply searching the parameter space of the theory is almost guaranteed to produce gravity if and when it produces other forces and they've already found certain parameters again that yield EM and Gravity.
So what are these parameters?
Specifically it is the shape of the 11 dimensions in relation to one another. Unfortunately this is a geometry problem that has a lower bound of 10^500 possibilities. But these possibilities are in a single parameter, the shape of the dimensions. Compare this to QFTs minimum of 18 parameters which must all be fine tuned. M theory is a superior theory based on this. But it's a damned hard problem to solve and all indications are that there is something still more fundamental and therefore simpler, but to arrive at that we either need a revolution in thought similar to Einstein which is something that happens only perhaps once a millenia, or we need to take what works with our existing theories and keep working them until we figure out literally "the shape of the thing".
So yes, M theory actually produces lots of physically testable predictions. The problem is that they are not testable with current technology and the search space if really, really huge. Perhaps if we had access to a black hole and some metric craptons of unobtainium we might be able to physically test these things and start whittling them down. But the same was true of QM and GR a mere 100 years ago. So my guess is that we will have the field narrowed down in short order a grand unified theory of everything is just beyond the grasp of our current technology and abilities to test.
We've had modern versions of M theory only since the 1990s. That's a mere 20 some years. If you want this process to hurry up, then instead of knocking it, learn about it and pitch in. Science is the ultimate open source project and what better project could you possibly contribute to than trying to decompile the source code for the omniverse?
(Score: 2, Interesting) by Anonymous Coward on Sunday December 30 2018, @09:20PM (9 children)
I'm a physicist with a PhD.
i want money to go into fusion research and building a colony on Mars, not string theory and a bigger version of the LHC.
I want intelligent young people (i.e. grad students) to work on making technology more energy efficient, food production cheaper, and climate change mitigation schemes. I want them to build a space elevator so we can get off this rock already and establish self-sustaining colonies that won't be wiped out when asteroid/nuclear bomb or whatever happens.
I DON'T want them wasting their energy and getting high on highdimensional imaginationland.
I agree that the theories are beautiful and worth studying, but we have limited resources.
general relativity and quantum mechanics are incomprehensible to most people, and they are beautiful imaginationland births, but they were generated because there were EXPERIMENTS pointing to problems (photoelectric effect and conceptual contradictions between Newtonian gravity and special relativity). If your theory makes predictions that are, in practical terms, out of reach of experiments, then it's not a theory. it's just pretty math.
I will not agree to giving money for polock's "paintings", and I will not agree to giving money for string theory research.
if you as a private person want to work on it with your resources, or fund someone to do it, go ahead.
but I think society has better things to focus its money and labor on.
(Score: 4, Insightful) by johnlongjohnson on Sunday December 30 2018, @09:47PM (3 children)
Clearly you're not.
First off a physicist with a PhD would understand the applicability of fundamental research to each of the topics listed as "want".
Secondly you're posting AC.
Thirdly if you had anything above a high school diploma, you'd understand that the general public doesn't have to understand a theory in order to reap it's benefits. For example GR is why GPS shows you being home rather than several miles away. And you'd understand why QFT is absolutely fundamental to modern solid state electronics and upcoming spintronics. This list is actually endless so I'll leave it with those two.
Fourthly your definition of a theory without practical experiments being "just pretty math" is flat wrong. Math itself is an experimental tool. It is a way of exploring and experimenting with things that are beyond our current tech and it is precisely how we devise tests that might be physically realizable either now, in the past or in the future. For example Bell's inequalities in the 1960s leading to us being able to prove entanglement via Aspect et al in 1982 which has lead to huge advancements in everything from fiber optics to information theory.
The fact is string theory, M theory etc currently serve to inform modern QFT and GR researchers about which directions to look to expand their theories. And yes we do get predictions that are unrealizable or intractable under certain formulations of QM without tossing in M theory. For example AdS/CFT correspondence has been instrumental in solving the black hole information paradox. In that way, these theories serve as a short cut through the endless math in much the way that Feynman's path integral formulation and perturbation theory have served as shortcuts through the intractable infinities in earlier theories.
So yes it's math, and yes it's pretty.
But deciding you don't like a theory because disregarding it to focus on immediate practical applications, is now the cool hipster thing...
Well it just shows you're a hipster, and the inability to think beyond the now and perhaps the immediate future, shows you're probably a millennial.
Sorry to break it to you but fundamental research doesn't work that way.
(Score: 0) by Anonymous Coward on Sunday December 30 2018, @10:13PM
I made a point in distinguishing between GR and quantum mechanics, on one side, and string theory on the other.
I didn't decide I don't like string theory (in fact I would love to have the time to learn it properly). I am saying that we have limited resources, and currently our best and brightest are busy trying to solve a nonproblem. They have beautiful math that can describe everything, and absolutely no empirical method to pin down the description enough in order for it to be useful.
Either come up with a theory that is descriptive, or start working on other problems (that humanity is having), because the theory you have now does not describe the real world. At best, it describes many worlds and ours is one of them (and we have no way of telling which) --- which essentially means it's not a theory of our world.
Here's a different way to put it. It's wrong in the particulars, but mainly right: I have a opaque box with billiard balls inside.
You can make an infinity of correct theories of how the balls interact based on their color, all of them correctly predicting how the box reacts to outside inputs, all of them incompatible, all of them predicting different things that will happen when we finally have a knife sharp enough to cut the box. But if nobody is working on sharpening the knife, all of those theories are useless.
(Score: 0) by Anonymous Coward on Sunday December 30 2018, @11:16PM
You sound like the posters above who don't understand string theory so they claim it is false.
If you disagree with the PhD then mod the post "Disagree". But you can't claim the poster is not a PhD because s/he posted as an AC and you don't like their opinions.
(Score: 1) by khallow on Monday December 31 2018, @08:01AM
I have a PhD in math (area was QFT) and I mostly agree with AC. There's a difference between fundamental research and useless research.
WRT string theory, there's two things to keep in mind. First, it's incredibly cheap as far as research goes and does have some utility on the math side. On the former, the world-wide effort of string theorists is probably a couple of orders of magnitude cheaper than the LHC. Even if it never pans out as a physical theory, it's still making a positive contribution to our understanding of math approaches to this situation.
Second, where's the testable predictions? It's not fundamental physics research, if it doesn't have those predictions!
If only that were true. The cool hipsters seem to be on the other side of that particular argument. I've never seen a lot of people criticize the way science is done. It should be more than it is.
Back at you on that. This is the "throw money at the wall and find out in a few decades whether any of it stuck" strategy.
My view on this is that if you can't show any sort of near future benefit - which can include merely bettering our understanding of the problem, its math, etc. - then you're not doing research, fundamental or otherwise, you're just cashing checks.
(Score: 0) by Anonymous Coward on Sunday December 30 2018, @11:24PM (4 children)
"but I think society has better things to focus its money and labor on."
The amount of money society "wastes" is truly monumental.
Did you know some people consider space exploration a waste of money while others consider the whole sports industry a waste. Why not go after one of the huge wastes ... Like plastic shopping bags... Ban them and save $4billion/year
https://conservingnow.com/plastic-bag-consumption-facts/ [conservingnow.com]
(Score: 0) by Anonymous Coward on Monday December 31 2018, @12:18AM (2 children)
Clearly, people value having plastic shopping bags at more than $4billion, otherwise they wouldn't spend that on them.
That there might be externalities that you don't like and which would be mitigated by a legal ban doesn't mean you are saving $4billion, if just means you are using legal means to control other peoples' behaviour.
The correct method is to determine the cost of the externality and charge it to the people making and using the plastic bags, and then to use that money to correct the problem. That is the important bit.
If it is not enough money to fix the problem, you raise the tax on bags until it is. At some price point people will start using less plastic bags. At some further point in the ratcheting tax, the money collected will be enough to fix the problem.
(Score: 1) by khallow on Monday December 31 2018, @08:03AM
And if that change of behavior doesn't happen at a price point that reflects the real externality, then it's a solid indication to move on, the problem doesn't need to be solved any further.
(Score: 0) by Anonymous Coward on Monday December 31 2018, @02:18PM
You are going to need 1000% tax on a 10 cent bag to even get people to notice. It is incandescent lights all over again, the current inefficient product is just too cheap and as long as it is even available people will keep using it. The alternative is to bring your canvas bags or re-use the store's boxes (from incoming shipments). other countries like the Philippines have done bans and just like incandescents, the US will be one of the last countries to implement a ban.
(Score: 2) by RandomFactor on Monday December 31 2018, @02:11AM
Cost to retailers of $4 Billion/Year does not mean that eliminating them will save $4 Billion a year and could easily result in highers costs, pollution and carbon footprint.
More details here on Paper vs Plastic
http://www.allaboutbags.ca/papervplastic.html [allaboutbags.ca]
В «Правде» нет известий, в «Известиях» нет правды
(Score: 0) by Anonymous Coward on Monday December 31 2018, @12:40AM
A Conway game of life's hypothetical aware creature sees the universe in terms of full/empty cells. Theoretically it can come up with a unified formula that codifies all the rules of the simulation but it's no better, in fact it is worse because needlessly complex, than the mere list of rules. So personally I am more interested in experiments and outcomes than in interpretations. But whatever I think should not bother you in your quest. Have fun.
(Score: 1, Troll) by Azuma Hazuki on Monday December 31 2018, @02:13AM (1 child)
What's wrong with this place is we have a festering, suppurating right-wing nutjob infestation. Those folks, you may have noticed, have an anti-intellectual streak a mile wide. As hangers-on, we get the tech-head mediocrities who have fairly deep but very narrow knowledge in one or two fields and think they've got a PhD in Everythingology; there is substantial personality overlap between these two groups, as well.
I am "that girl" your mother warned you about...
(Score: 3, Interesting) by Bot on Monday December 31 2018, @07:02PM
Your comment history, and the one of those who debated you, is out there. One can count the ad hominem vs actual arguments. The lumping together of people based on a couple metrics oppa Nazi style and talking about anti intellectualism in the following sentences is a troll gem, good one!
Account abandoned.