Slashdot Mirror
Can String Theory Accommodate Inflation?
David Shiga writes "String theory is the leading contender for a "theory of everything" that could unite all the forces of physics. But a recent study suggests that it may be more difficult than scientists had hoped to square string theory with inflation — the widely accepted notion that the early universe had a period of especially rapid expansion. Some say this could even lead to the abandonment of either string theory or inflation, though no one is ruling out a possible resolution yet."
Actually it is 'evolution'. Because everytime an obstacle comes up, string theory is changed in another untestable manner to accomadate an uncomfortable reality that it is not really science.
I've never understood how string theory could ever be validated, except through funky math invented for the purpose. It's my understanding that if you enlarged an atom to the size of the universe a string would be about 50 feet long (about a planck length). How is that ever going to be testable in practice? From all I've read, the energy required is just not possible, ever.
by M-theory. My understanding is that there are 5 different versions of 10-dimensional string theory that can be generalized to 11-dimensional M-brane theory. Not sure about the inflation thing though, I just wanted to throw in the fact that you are talking about an old theory.
I didn't believe that when I read it so I worked it out and found that that' actually true (to within an order of magnitude).
Um...physics has completely turned upside down in the last century and has changed pretty dramatically over the last 20 years. What kind of remote island are you living on that you're so out of touch and think that 'different' approaches never get funding? If you've never bothered to look at current research then you really don't have any right to speak, and it's obvious that you haven't. For example there has been ongoing debate for many years now between people who are searching for dark matter and proponents of MOND. There's nothing more annoying than pontification from ignorant armchair physicists.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
If it can't be tested, it's not science...it's pseudoscience.
String theory is the sort of intellectual game normally played by religions. There's always a part which can never be tested or disproved and that's where you'll end up if you start a "debate". An impasse is the best you can ever achieve if you try.
No sig today...
Um, yeah. You see I'm going to be extremely skeptical of anyone claiming that the sun cannot be performing fusion when based on the very same theories that describe the pressures and energies required for fusion occurring in the sun we have created fusion right here on earth.
/., he was claiming that EU explained impact craters, as if EU had now replaced the obvious and rather well tested effects of kinetic energy. Einstein didn't and simply couldn't up-end Newton's theory, he could only explain what Newton failed to. EU tries, and summarily fails.
I'm skeptical of anyone who claims not only to have solved problems with the existing theory, but to entirely upturn the existing theory itself even the parts that have extensive verification. Hell the last time I crossed baths with an Electric Universe proponent on
Epicycles were a case of taking something with a clear explanation -- elliptical orbits -- and deciding that no, everything must be comprised of circles. EU is the same thing -- attempting to turn everything into the universe into electricity, desperately inserting it everywhere even if there is no need.
It's one thing to try to explain the things that our current theories can't. It's quite another to try to invalidate well-verified aspects of those theories.
I'm no fan of science politics in this country, but the most basic bar for any theory is that it should not contradict the existing evidence. Relativity could do that, so even as weird and unlikely and unorthodox as it was considered at the time, it eventually won acceptance and now is one of the best tested theories. EU can't do that, and thus even in a perfect system should be rejected.
The enemies of Democracy are
String theory is probably the only theory that really supports inflation. If the net energy in the universe is constant, then the net curvature must be constant, therefore it could only appear smaller if curvature were balanced between other dimensions.
We at slashdot are scientists, specialists and kernel hackers. Your FUD will be found out.
I'm not a string theorist, but I am a cosmologist. Here are some thoughts:
Inflation has not been "confirmed" in away way. It's the best explanation for a very very limited number of datapoints we have on the "early" Universe. Very smart people (e.g., Sean Carroll, now at CalTech) have made convincing cases that inflation is actually incoherent in important ways. I have spent quite a bit of time trying to come up with alternatives to inflation, and it's damn hard -- it "works" very well, in the sense that it solves a bunch of problems all at once that are hard to solve individually. But it does invoke plenty of nonstandard physics we've never seen in the Universe, let alone the lab.
Inflation and dark energy are deeply connected. They both require something called "negative pressure". Negative pressure is bizarre, and actually is from a Newtonian perspective a violation of the conservation of energy (in General Relativity, energy is not conserved -- rather a complicated combination of numbers some of which refer to what we'd measure as energy is conserved.) Negative pressure means that if you take a box of the stuff, and let it expand, at the end of the day there's actually more stuff in there than you started with.
String theory should better be known as "a collection of approaches." It does not have the coherence of, say General Relativity, which is a mathematically closed system. Talking about "giving up string theory" is kind of dumb -- essentially what you are saying is "do not try to do the following large class of calculation." There are definitely competitors to string theory, but none have captured the attention of a highly fractious community the way string theory has.
Not sure if anyone's still reading this thread, but I'm happy to talk more about it. Reply with questions if you like!
Protect your liberties. Donate to the ACLU
Some versions of string theory do make a genuinely interesting prediction. They predict a particle that hasn't actually been observed. A large class of the most studied string theories require adding just this one particle to the standard model, and it has to have spin 2, and mass 0.
That's a great candidate for a graviton, which is also being predicted for some other reasons. When some of the most aestetically interesting versions of string theory turned out to predict not just any particle or whole family of particles, but that specific one, many physicists got more interested in those theories.
However, general and special relativity don't actually predict gravitons - Einstein was able to treat gravity as a strain inherent in space-time and not as something mediated by a particle at all, and get some very testable results. Quantum Mechanics doesn't really require Gravitons either. Actual particle accelerator experiments have satisfied various symmetry theories from just the particles observed, and this again doesn't include gravitons.
There's no practical way to build an accelerator that could even theoretically reach the energies needed to test unification of all four fundamental forces, and gravity is the odd man out that we have no expectation will be integrated by either accelerator experiments or astronomical observations.
Proof of a mediating particle for gravity would still not prove any of the string theorys, but it would give the likelyest of them some fairly strong support. For now, we're stuck - a theory looks mathematically beautiful, and actually makes a prediction, but we aren't sure yet if that prediction is ever going to become testable, and on the other hand we have no categorical proof the prediction is fundamentally untestable. A test would be nice, but so would a stronger reason for saying there could be no test than just that we aren't yet a type 2 civilization, with the energy of a whole galaxy to use, so we are limited by the economics of it.
Who is John Cabal?