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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."
Dark matter is certainly a bizarre hypothesis, and the question you ask is natural - couldn't we just be wrong about gravity? It's somewhat easier to believe that Einstein's general relativity is modified than that the universe is filled with so much mysterious, unseen "stuff". This is the basic idea behind MOND (MOdified Newtonian Dynamics) theories, which has received a good bit of thought among physicists.
MOND doesn't look like the right solution, however. The last 2 or 3 decades have provided an enormous amount of observational data about the structure of the universe (large scale structure, galactic dynamics, gravitational lensing, light element abundances, the cosmic microwave background...), all of which is basically consistent with the simplest dark matter model ("cold dark matter") and inconsistent with any modified gravity theory. We don't need to imagine any particularly exotic properties to the dark matter, it just needs to be something that doesn't interact with electromagnetic forces (just like a neutrino only much heavier). Even very complicated MOND models fail to match observations, however (unless you add in a bunch of dark matter anyway).
Perhaps the most striking example is provided by observations of the Bullet Cluster last year. Basically we've found a pair of colliding galaxy clusters where the collision has separated the dark matter from the ordinary matter somewhat. Skipping over the details, this provides dramatic evidence that dark matter is real "stuff" - in essentially any modified gravity theory without dark matter, the gravitational forces still have to be coming from the same place as the visible matter! This is a very general argument, and observations like this have more or less put the nail in the coffin of MOND theories.
Astrophysicists are almost universally convinced at this point that something like dark matter exists. We're starting to map its distribution in detail throughout the universe, and the next major challenge will be determining its makeup - either by production in an accelerator or detection in dedicated experiments.
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.
/sarcasm
Right so Newtons theory of gravity was perfectly good enough and Copernicus's theories were just fine as well. No need to revise for data.
How on earth did this get +2 interesting. please mod it '-1 author should never breed'.
Evolution like all scientific theories are either rejected or modified over time. If there is enough data that contravenes the theory then the theory is rejected. If a little data points to an error in the original idea then it's modified. Evolution has never been rejected because the core idea is right but things like the mechanism and some subtitles must be changed as data came in.
The conversely the arguments against string theory never needs revision because the formula can accommodate almost every possible observation.
"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."
I read a few of the arguments from the page, just to know what you are talking about.
Neither Einstein's relativity nor quantum mechanics are physics so we cannot use them as a foundation for our new model (although we should find that the mathematics that works in the real world still applies).We have to discard "modern" physics and return to the classical physics of a century ago. This, perhaps, is the greatest hurdle - to discard our training and prejudices and to approach the problem with a beginner's mind.
whew! I'm so glad we can at least keep mathematics - or some part of it - because reinventing physics without it would be problematic
We must "go down" one more level and propose that all subatomic particles, including the electron, are resonant structures of electric charges of opposite sign that sum to the charge on that particle....The electron is not a fundamental, point-like particle.It must have structure to provide its dipole magnetic field.... The same model applies to the proton and the neutron.
So all the particle physics results indicating the existence of quarks are fictional? Well if we had known they didn't exist we wouldn't have spent so much time and money pinning down their properties.
When we accelerate electrons or protons in an electromagnetic field they become less responsive to the fields the more they are accelerated. This has been interpreted as an increase in mass. However, charges have no mass.
I (and particle physicists) much prefer E^2 = (pc)^2 +m^2*c^4 where m is the rest-mass; an unchanging invariant property. only the momentum p has relativistic terms in it.
The notion that matter can be annihilated when normal matter meets antimatter is a confusion of language. Matter can neither be destroyed nor created nor can matter be exchanged for energy. Einstein's E = mc2 refers to mass, a property of matter, not matter itself.
The most collapsed form of matter is the neutrino, which has a vanishingly small mass. However, the neutrino must contain all of the charges required to form two particles - a particle and its antiparticle. This symmetry explains why a neutrino is considered to be its own anti-particle. A neutrino may accept energy from a gamma ray to reconstitute a particle and its anti-particle. "Empty space" is full of neutrinos. They are the repositories of matter in the universe, awaiting the burst of gamma-radiation to expand them to form the stuff of atoms. The weird "zoo" of short-lived particles created in particle accelerators and seen in cosmic rays are simply unstable resonant systems of charge.
We must abandon our peculiar phobia against a force acting at a distance. And we must give up the notion that the speed of light is a real speed barrier. It may seem fast to us, but on a cosmic scale it is glacial. Imposing such a speed limit and requiring force to be transmitted by particles would render the universe completely incoherent.
Holy friggin' hell. check out http://www.physicstoday.org/vol-56/iss-10/images/p48fig1.jpg or http://en.wikipedia.org/wiki/Image:First_Gold_Beam-Beam_Collision_Events_at_RHIC_at_100_100_GeV_c_per_beam_recorded_by_STAR.jpg image created at RHIC. Think about what standard physics implies about the result versus "Electric physics"
Electric Physics
1. individual gold atoms are accelerated perhaps to >c
2. energy is added into some electric fields within the atom
3. the electric fields do not interact with any neutrinos until the atoms near each other
4. the electric fields interact with thousands of undetected neutrinos at the exact point where the atoms collide (kind of
three questions to answer! I will go in order.
1. I have many many positive things to say about Lee. He is a terrific guy, and one thing he deserves special praise for is that he loves talking to, and taking seriously, younger researchers like me. I buttonholed him on his last vist and we talked for a while about my inflation alternative and he was critical but also encouraging -- a hard note to strike.
Lee is also a great "cherrypicker", he finds neat things in different parts of physics and brings them in. We actually had (twenty or thirty years apart) stumbled on a couple unusual facts in the literature for condensed matter and had a good chat about applying them to cosmology. That said (you could see this coming huh?) Lee's criticisms of string theory have angered a lot of string theorists -- and in such a way that I think Lee maybe should take some of the blame for being overly confrontational.
String theory these days is looking for ideas and data, and so lots of people do so-called "string cosmology". It is very much in its infancy, and many (including myself) consider it something to dabble in but not to build a career on (yet.)
2. cosmology has some "big" questions. Essentially, many all boil down to some uber fine tuning. The universe needs to be expanding at just the right rate to have survived this long, and it's very strange that it is. To put it another way, OK: we believe that when the universe was very young, all the physics had to do with the very tiny Planck scale -- the scale at which quantum fluctuations form black holes. You can just combine the constants G, c, and h together in different ways to get the length, time and mass associated with this phenomenon. For example, if you accelerated an electron until it's (relativistic) mass became about 10^-5 grams and crashed it in to something, you would expect that in order to describe the event correctly you would need to describe how the crash produced miniblackholes.
So instead of making the Planck mass, change the constants around to get the Planck time. It's unbelievably short -- 10^-44 seconds. We expect all the physics back then to have roughly this timescale. Basically, you assume that whatever the equations are, the terms are going to have dimensionless coefficients of order unity, and then the rest pops out. (In the same way, say you had a funny oscillating system -- not a simple harmonic oscillator, but something wayyy more complicated. There will still be a constant in there with dimensions (force)/(distance), call it "k", and there will be a mass for the system. From that you can make a rough guess at the period -- sqrt(m/k) is the only combination that gives you time.) Sorry to belabor this if it's obvious to you!
Anyway, there's something glaringly obvious. The Planck time (10^-44) is much smaller than the age of the Universe today (10 billion years.) How did the physics back then "conspire" to give an answer so wildly different? That's how we know it's going to be a tough problem.
As for the 10^500 thing -- that's the question of the string theory "landscape". The basic thing is that string theory is a perturbative theory right now (one of Lee's big criticisms, and potentially very valid, although it's how every other non-gravitational quantum theory works) -- you can basically do calculations against a "background". Perturb the background a little, and gravitons are produced -- string theory can tell you their scattering amplitude, a massive victory. We used to think that the choice of the background would end up being "obvious". Now there's the suggestion that there are maybe 10^500 different choices and it makes a difference. Still a controversial thesis however!
3. Ah, yes, I see you already know about this whole background thing. I think Lee is going down a bit of a rabbit hole with the whole background indepedence thing. We've been doing thing perturbatively for years, and it's enabled us to calculate all sorts of things that go on in colliders (although
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