The current state of string theory and general relativity

[Chaotic42]

I am a senior mathematics major and I'm taking some entry-level geography classes for my minor. Before one of these geography classes, the class got on the subject of the speed of light, relativity, and string theory.

Now, I'm not an actual scientist, but I'm always skeptical. However, I also know that I really don't understand much about relativity (on a technical level) and I know virtually nothing about string theory beyond the popular science books that I imagine many of us have read.

One student quite confidently said that string theory is dead and much of relativity is being debunked. Apparently the student "read some papers... from MIT..." I didn't get a chance to ask for specifics.

My understanding is that string theory openly acknowledges that there are currently no mechanisms for testing any of its predictions, but there is nothing that is specifically excluding it as a possible description of our physical system. My understanding is also that general relativity is alive and well, and that it is actually being verified on a rather consistent basis.

Now, I know that people say things all of the time, and that people who tend to be insistent without proof often turn out to be full of crap. My gut says that's what's going on here. However, I'm curious if any of you have come across any valid source information that might confirm what this other student was saying.

I haven't been able to, but I haven't done much looking. I'm just kind of curious to see if I'm just completely wrong.

Thanks.

 

[Modelworks]

The topics you are touching on, string theory and quantum mechanics, are both rapidly changing fields where what it considered right today may be proven wrong tomorrow. A good explanation of the different viewpoints is in the documentary series fabric of the cosmos.
http://www.pbs.org/wgbh/nova/physics/fabric-of-cosmos.html

General relativity has not been totally proven wrong, just some parts of it that don't fit well with new discoveries so new theories are being created to address those problems.

 

[Anteaus]

I don't relativity will ever be proven wrong, however context might change. The problem with theoretic physics today is that much of it can't be tested and most of it's credibility is based on how much the ideas play well with observed phenomenon. I'm not saying that string theory doesn't have a viable place in how we see the universe, but gravity and time dilation are observable in real world application so if they really plan on reinventing the wheel (so to speak), it will only be through a truely earth shattering discovery, and at this point all they have is a few good ideas.

 

[Farmer]

To qualify myself, I am not a physicist. I did major in physics during college, but I am now doing research in more of an applied physics field concerned with condensed matter. It is far from the cutting edge of theory. In other words, I know more about physics than the average person, but have no deep understanding of general relativity and certainly no understanding of string theory at all.

So first off, all physical theories are incomplete. They predict some things very well, but others not so much. For instance, F=ma can predict rocket's trajectory quite well, but cannot predict the behavior of electrons in metals. To assume that we can find a totally complete theory that explains everything is a bit pretentious.

What is a successful physical theory? It is one that can make predictions on observables that can then be confirmed with experiment. In that regard, general relativity can be considered successful. For instance, it predicts with great accuracy the effect of gravitational lensing, which was observed experimentally as early as the late 1910s and has since been verified extensively by more precise experiments. Of course, ongoing research may provide experimental results which contradict a prediction made by GR. This doesn't make GR wrong or useless, it just highlights an area where it may be incomplete.

I know nothing about string theory so I can't comment, but certainly it is not successful in this regard.

Maybe the mystique or controversy surrounding both GR and string theory is they are nonintuitive and highly mathematical theories which make predictions about physics in totally non-human scales (GR is offered as a course only to doctoral candidates in theoretical physics, string theory is "more math than physics"). As a result, it is inaccessible to the layperson in both regards. It is esoteric "ivory tower" research that the public finds difficult to understand and/or see the value in.

I dislike it when people (especially if they are just seniors in college) make broad sweeping statements like "X and Y theories are totally wrong." I mean, everyone is taught now that Newton's Laws are actually "wrong" and that quantum theory is the deeper theory. But does that make classical mechanics wrong, or useless? Absolutely not. Does it make it a worthless topic to study? Absolutely not. In fact, you'd be hard pressed to gain any understanding of any quantum theory without first understanding classical mechanics.

I cannot speak about string theory because I don't understand a lick of it. I really doubt your classmate understands much of it either.

I can tell you that in no way has general relativity been "debunked."

 

[Chaotic42]

I dislike it when people (especially if they are just seniors in college) make broad sweeping statements like "X and Y theories are totally wrong." I mean, everyone is taught now that Newton's Laws are actually "wrong" and that quantum theory is the deeper theory. But does that make classical mechanics wrong, or useless? Absolutely not. Does it make it a worthless topic to study? Absolutely not. In fact, you'd be hard pressed to gain any understanding of any quantum theory without first understanding classical mechanics.

I cannot speak about string theory because I don't understand a lick of it. I really doubt your classmate understands much of it either.

I can tell you that in no way has general relativity been "debunked."

Heh, this person says a lot of things of in that matter-of-fact kind of way. For some reason this one just rubbed me the wrong way today. Unfortunately, since I've only had basic university physics, I had no way of proving that it was essentially a load of crap. Without the ability to back up an argument, I can't really say anything.

 

[soccerballtux]

Answer not a fool according to his folly, lest you look like him.

 

[PsiStar]

This wiki provides a sort of time line of some of the theories and why they lose disfavor. Otherwise it is pretty difficult to jump into the middle of an already random discussion.

Skepticism is always good in these discussions AND to come across as merely the reporter of information than an evangelist.

 

[Wizlem]

I'd have to agree with farmer on most points. I also graduated majoring in physics and as an undergrad I didn't learn anything about general relativity or string theory. Everything taught was much more focused on quantum mechanics.

I would also have to say that string theory is probably the most publicized subject in the field and if it was dead you could easily google to find out. Relativity being debunked would also have numerous lay person articles as well. That kind of stuff doesn't stay hidden in some MIT paper.

 

[Pheran]

Until string theory is capable of making a testable prediction, it's not science, but a fanciful exercise in mathematics. It seems to be one of those things that sounded elegant at one point but just never panned out.

Relativity will never be "debunked", that's just nonsense. However, it certainly might be modified, much like it modified Newtonian mechanics.

 

[wuliheron]

String theory is 40 years old and has yet to produce anything really useful other then some advanced mathematics. The mathematics are incredible and worth exploring further, but your friend is essentially correct that the theory itself is loosing ground in physics. The newer theories are all contextual, while string theory is a background dependent holographic theory.

Essentially experiments in the last couple of decades have driven the final nails in the coffin of the idea that there might be a convenient loophole found in quantum mechanics. Indeterminacy remains as mysterious as ever and now even entanglement has proven to be subject to indeterminacy. Instead the evidence has been growing that quanta are contextual, that is, how we perceive them depends on the context. Whether we measure the cat as dead, alive, or somehow both at the same time could be just a question of the context of the measurement.

For an interesting discussion on some of the mathematical implications I recommend this thread at another website:

http://forums.philosophyforums.com/threads/wittgenstein-on-infinity-53625.html

The author of the thread is a professional philosopher of cosmology and knows his physics.

 

[silverpig]

I did astrophysics for my undergrad and will echo most of what Farmer said. I actually did a GR course in undergrad which was quite interesting. I struggled with it at first as I was trying to imagine the motions of objects in a real sense. It wasn't until I essentially dissociated the course from reality and just lived in the math that I got it.

The math is pretty messed up but it is quite interesting once you get it.

As mentioned GR has been tested since the early part of the 1900s (the first eclipse experiment was actually in error and they messed it up). If GR wasn't true, GPS wouldn't work. It is still very much alive in the experimental realm of physics.

String theory is far from dead too. The prof that taught me GR was doing quantum gravity theory using string theory.

 

[wuliheron]

Well yeah, it's still popular among physicists because of its elegance and it still has insights to offer, but it's definitely loosing ground. The situation is similar to what happened with the old theories of the aether where each passing decade the theories just got wilder and less believable. So far we've gone from more mundane theories about hidden variables to Bohmian mechanics to panpsychism to theories proposing an infinite number of universes. It's all very entertaining and has given physicists at least some idea of what to look for, but I wouldn't give too much credence to any theory that hasn't proven itself in many decades. Bohmian Mechanics is now 80 years old and still going strong.

 

[William Gaatjes]

IMHO :
All there is are oscillations in this aether (quantum fluid or virtual particle sea) however you want to call it.
When for some yet to discovered reason, these oscillations stay in resonance and become self sustaining in combination with the environment (Heisenberg : you cannot measure without influencing what you measure). Discovered as particles.
There will be infinite particles to be discovered. Which is good to create an understanding and in the end a mathematical model, but that model will not even execute at this moment while combining all calculation power currently found on the planet. Nor will it for years to come. Which we are very comfortable with... ^_^.
Time is used by humans because the way the mind works. The mind arises form the body. The mind is based upon laws of nature.
Reality really is that all is happening at once. But luckily a universe creates limits of propagation. And thus time has a meaning. Because of relativity.
Reference frames become important. Imagine how the universe would look like if the speed of light would be infinite. To make it easier, imagine how photons can affect the electrons of an atom. Imagine how a photon could affect an electron if there would be no limit to the speed of light. Imagine how a plant on this planet should use uv-rays to power the chemical reaction that is called photosynthesis if the speed of light would be infinite.

Remember transmission lines and how high speed electrical signals are transferred through a conductive medium ? That it is not the electrons themselves that move at high speeds but instead transfer energy (see it as information for a moment) ?
Imagine for a moment that these electrons pass on photons for a short moment. Just think of the cradle of Newton :

Imagine how an electron would interact with a nucleus if the speed of light would be infinite... How electrons would pass on information if the speed of light would be infinite. Repeat all these thought experiment with half the speed of light and with double the speed of light...

http://en.wikipedia.org/wiki/Newton's_cradle

And yes, multiple universes are possible. But do not have to be compatible...

Here, this is about transmission lines and is a good way to think about the how and the why of laws of nature or better explained, the laws of this universe...
http://dl.dropbox.com/u/45177488/transmissionlinesmall.pdf