Is String theory a dead end?

[kk434]

It has been under developement for 20 years and it only gets more complicated. Even worse, impossible to experimentally test unless you reach the Planck energy scale. I think this theory is getting less and less attention from scientists.

 

[ramparts]

On the other hand, it might be true so it would be kind of silly to just give up on it.

Technology will get there eventually. We don't have to recreate Planck scale conditions - the Universe has already done it for us, and that may be possible to probe in the somewhat near future. But eventually, we'll be able to test it because we do need to know what goes on at the Planck scale. That's the next frontier of physics.

 

[darkmatter4brains]

There have also been ways proposed to indirectly test the theory.

One example is the existence of extra dimensions, which are predicted by String/M theory. In fact, the LHC may be able to look into this if the extra dimensions are on the high side of the size scale that has been proposed. Even if it doesn't find them, it narrows the range and eventually it's possible some other collider could detect their existence.

In addition, M Theory cosmology will get an indirect test from the Planck satellite. Basically, IIRC, it's looking for the polarization in the CMB. If it finds it, that supports Inflation. If it doesn't, it supports M Theory cosmology. If M-Theory cosmology gets ruled out, that doesn't really spell doom for M-theory, but, if it starts to get confirmed, it does make M-theory look more likely.

 

[ramparts]

In addition, M Theory cosmology will get an indirect test from the Planck satellite. Basically, IIRC, it's looking for the polarization in the CMB. If it finds it, that supports Inflation. If it doesn't, it supports M Theory cosmology. If M-Theory cosmology gets ruled out, that doesn't really spell doom for M-theory, but, if it starts to get confirmed, it does make M-theory look more likely.

Got a source for that? Sounds like a pretty big oversimplification to me. We know there'll be some polarization in the CMB, what matters is how strong the tensor modes will be and what the power spectrum will look like.

Also, I was unaware that "M theory cosmology" was an alternative to inflation? I thought that string theory/M theory was potentially able to account for inflation.

 

[darkmatter4brains]

Best source I've seen is the Planck Bluebook itself:

http://www.rssd.esa.int/SA/PLANCK/docs/ ... 291_V2.pdf

there's a whole section devoted to String Cosmology. An earlier section also covers the polarizations of the CMB

You're right, there is also brane inflation. As to be expected, we have to still account for the horizon problem abnd flatness problem. BUT, as I understand it, the mechanisms for brane inflation are different than under Alan Guth's Inflation theory. One would lead to polarization of the CMB and the other shouldn't. You can note on page 57 that they mention there would be no tensor modes under the brane inflation model under question there.

Also, on reading another section closer, it does sound like depending on the string tensions, polarization could show up, but would be very different from the polarization under Alan Guth's Inflation model.

I think the overall gist is that one model is expected to effect the CMB polarization differently than the other. Depending on what signature they find in the CMB polarization it will lend more support towards one of the theories (or neither, I suppose. Wouldn't that be cool!)

That's all the details I know about that

 

[ramparts]

Oh yeah, that's definitely true - Planck's polarization could very well shed light on inflation and even quantum gravity. But it could very well not. Luckily there are some ground-based polarization experiments that are going to be probing the question fairly soon at higher resolution (but without full-sky coverage).

And I think I was more taking issue with the suggestion that under some scenarios you'd find no polarization. There are absolutely tensor modes in there, it's just possible there aren't any from inflation

 

[kk434]

This polatization deal is very complicated, try to read this one. http://www.infim.ro/rrp/2009_61_3/art17Stefanescu.pdf
According to thier findings Planck can either prove or disprove the inflation theory. But i think you must be at least PhD to understand what is the connection betwen the B-mode polarization an inflation.

 

[darkmatter4brains]

Luckily there are some ground-based polarization experiments that are going to be probing the question fairly soon at higher resolution (but without full-sky coverage).

Do you recall what those ground based ones are called? I wasn't aware of those, but would like to try and follow those along with Planck. This is pretty neat stuff and has the potential to shed some light on some really big questions!

This polatization deal is very complicated, try to read this one. http://www.infim.ro/rrp/2009_61_3/art17Stefanescu.pdf
According to thier findings Planck can either prove or disprove the inflation theory. But i think you must be at least PhD to understand what is the connection betwen the B-mode polarization an inflation.

sure is! All the guys working on it are probably post docs and beyond!

 

[raptorborealis]

It has been under developement for 20 years and it only gets more complicated. Even worse, impossible to experimentally test unless you reach the Planck energy scale. I think this theory is getting less and less attention from scientists.

20 years? I recall reading about it in 'Science Digest' in the early 70's while in high school. it was a topic I avoided like the plague in university even though it was the trendy rage. It went 'zip' over my head and still does. I latched on to geology as something i could sink my teeth into.

 

[ramparts]

This polatization deal is very complicated, try to read this one. http://www.infim.ro/rrp/2009_61_3/art17Stefanescu.pdf
According to thier findings Planck can either prove or disprove the inflation theory. But i think you must be at least PhD to understand what is the connection betwen the B-mode polarization an inflation.

Well, Planck's not going to "disprove" inflation. There are a ton of inflationary models out there and not all will be testable with Planck. But it does have a very real chance to confirm inflation, if it finds the BB spectrum it expects.

And you certainly don't need a PhD to understand the connection, a graduate student working in the field will have a perfectly fine grasp of it.

Luckily there are some ground-based polarization experiments that are going to be probing the question fairly soon at higher resolution (but without full-sky coverage).

Do you recall what those ground based ones are called? I wasn't aware of those, but would like to try and follow those along with Planck. This is pretty neat stuff and has the potential to shed some light on some really big questions!

Oh, there's a bunch out there, some of which (like QUaD) are already taking data, others (like SPTPol and ACTPol - polarization-sensitive receivers they're going to mount on the SPT and ACT CMB telescopes) should be up soon, and yet others (like CMBPol and others whose names I've forgotten) will be really high-res and are a few years away. Wiki has a good list:

http://en.wikipedia.org/wiki/Cosmic_mic ... xperiments

And you'd probably be interested in the relevant Astro2010 white papers, which lay out the science that can be done with proposed missions in the next decade. Here are the white papers from CMBPol:

http://cmbpol.uchicago.edu/papers.php

The first one, Scott Dodelson's, is an especially good summary of the early universe cosmology you can do with CMB polarization. Almost all the white papers are on the arXiv if you want to search through.

 

[darkmatter4brains]

Thanks ramparts!

 

[EarthlingX]

www.universetoday.com : Scientists Say They Can Now Test String Theory

Sep 1st, 2010

by Nancy Atkinson

The idea of the “Theory of Everything” is enticing – that we could somehow explain all that is. String theory has been proposed since the 1960’s as a way to reconcile quantum mechanics and general relativity into such an explanation. However, the biggest criticism of String Theory is that it isn't testable. But now, a research team led by scientists from the Imperial College London unexpectedly discovered that that string theory also seems to predict the behavior of entangled quantum particles. As this prediction can be tested in the laboratory, the researchers say they can now test string theory.

 

[SheldonCooper]

I believe the fact that we have two flavors of string theory to contemplate, bosonic and heterotic string theory, makes the whole subject much more facinating. :ugeek:

SC

 

[dryson]

On the other hand, it might be true so it would be kind of silly to just give up on it.

Technology will get there eventually. We don't have to recreate Planck scale conditions - the Universe has already done it for us, and that may be possible to probe in the somewhat near future. But eventually, we'll be able to test it because we do need to know what goes on at the Planck scale. That's the next frontier of physics.

In order for science and physics to venture into the next frontier of physics the old roadblocks of General Relativity and Special Relativity need trash canned. There is no way possible that the next frontier of physics can be explored without first seperating ourselves from the chains that say this theory is not possible or that theory is not possible. While still holding onto the old system of physics that chase itself around like a dog that chases it's tail going nowhere.

 

[kk434]

The GR and SR have been tested so many times that there is no way that they will be trashed, Newtons old laws are still walid and hi didn't have a clue about modern physics.

 

[neuvik]

In order for science and physics to venture into the next frontier of physics the old roadblocks of General Relativity and Special Relativity need trash canned. There is no way possible that the next frontier of physics can be explored without first seperating ourselves from the chains that say this theory is not possible or that theory is not possible. While still holding onto the old system of physics that chase itself around like a dog that chases it's tail going nowhere.

So with your special brand of genius can you explain the photoelectric effect? Roadblocks...hah.

 

[origin]

interesting mostly over my head but interesting.

Dryson's post reminded me of the Sesame Street song:

One of these things is not like the others,
One of these things just doesn't belong,
Can you tell which thing is not like the others...

 

[emperor_of_localgroup]

So with your special brand of genius can you explain the photoelectric effect? Roadblocks...hah.

As far as I know photoelectric effect has nothing to do with SR and GR.

Btw, IMHO, photelectric effect was not worthy of a Nobel prize. Looks like it was easier to get a Nobel in the earlier years.

 

[ramparts]

Remember, Einstein didn't discover the photoelectric effect, he used the photoelectric effect to discover that light is quantized. That is absolutely worthy of a Nobel Prize. That's one of the most important discoveries in physics in the 20th century.

That said, I find it a bit odd he won the Nobel "especially" for that, rather than general or even special relativity, but you can't give the guy too many of them now.

 

[centsworth_II]

...I find it a bit odd he won the Nobel "especially" for that, rather than general or even special relativity...

Maybe they used his work on the photoelectric effect as a safe bet. Relativity was so revolutionary that although they may have thought it was probably right and worthy of a Nobel, they may have been worried that it hadn't been tested enough and didn't want to wait before awarding Einstein a prize.

 

[ramparts]

Yeah, I'd imagine that's what it was. General relativity had some pretty startling confirmation about two years earlier with Eddington's solar eclipse observations, but it was relatively untested and, more importantly, while GR then wasn't a big field, Einstein's work on the photoelectric effect spurred the work that dominated physics for the next couple of decades and led to quantum mechanics.

 

[neuvik]

As far as I know photoelectric effect has nothing to do with SR and GR.

Btw, IMHO, photelectric effect was not worthy of a Nobel prize. Looks like it was easier to get a Nobel in the earlier years.

Guess what you know doesn’t go very far teheh. The photoelectric effect was an actual road block in physics, to which Einstein’s work was certainly worth the Nobel prize. Giving him the Nobel prize for his work on the photoelectric effect is giving him the Nobel prize for Special Relativity. Relativity is a direct outgrowth from the study of electromagnetism. It’s because electromagnetism raised the question of “with respect to what does light go at speed c; in what frame of reference are the laws of electromagnetism valid.”

After the failure to prove the existence of luminiferous aether by the Michelson–Morley experiment there was a huge gap to those questions. Einstein came along, 1905ish with his paper "On the Electrodynamics of Moving Bodies,” and asserted his principal of relativity, and that there is no aether. Its basically restating the Galilean relativity. (Amazing we had the ground work for Special Relativity hundreds of years ago!)

“The Laws of Physics are the same for all observers in uniform motion.”

-Eisenstein 1905

Any frame of reference in uniform motion is perfect for conducting physics..or heck…playing basket ball. You play basket ball the same at the gym as you do on an aircraft carrier…even though the carrier is moving, just doesn’t matter. There is no special frame of reference, you don’t have to account for the fact the carrier is moving to play, or do physics experiments. (again, so long as its in uniform motion.

General relativity came along later to answer some questions about non uniform motion, but that’s for another thread.

Anyways stating that there is no special frame of refrence enabled him to declare that light was in discrete quanta, called photons. If we had to account for the aether, we would have odd cases, is the light going with or against the "aether wind," the aether would also have to be the primary frame of reference; so you would have odd ball things where a person would calculate light going faster than it should be, or slower. Its just a whole dark area talking about it, Realativity will never be disproven, maybe expanded on, but thats it.

 

[ramparts]

Relativity is an outgrowth of E&M (in a way), but not really of the photoelectric effect. What we learned from Einstein's work on the photoelectric effect is that light is quantized. That in itself has nothing to do with the real discovery about light which led to special relativity, which is that it travels at a constant speed in all reference frames. Relativity doesn't care if light is quantized. It was, at the time, a pretty much unrelated discovery.