# Has relativity been proved wrong?

1. Dec 19, 2012

### KeplerJunior

While explaining how science works in my biology class my biology teacher said that relativity had been proved wrong, except for with gravity, and had been replaced by a new theory.

Is this true? and if so what is the new theory and what are its principle ideas?

2. Dec 19, 2012

### PAllen

As stated, nonsense. Especially the comment about gravity which is general relativity. General consensus is that GR must be modified for certain situations. However, special relativity has no known or foreseen exceptions at the present time.

It might help if you asked what your teacher is referring to.

3. Dec 19, 2012

### Staff: Mentor

It's hard to know what your biology teacher meant, so it's hard to know how to answer. Perhaps the best thing to do is just give a quick summary of the current state of theories in fundamental physics.

First, a general note: a theory can be "wrong" in a strict sense and still be very useful. Newtonian mechanics is "wrong", strictly speaking, but it is still used extensively, because it's a good enough approximation for many purposes. I'm assuming that by "wrong", your biology teacher did not mean the theory is wrong the way that, say, "flat earth theory" is wrong, but only the way that Newtonian mechanics is "wrong".

That said, here's a quick overview of the current state of physical theories:

(1) For situations in which everything moves very slowly compared to the speed of light, and in which gravity is not too strong, Newtonian mechanics is a good approximation and is still extensively used, as noted above.

(2) For situations in which things move fast enough compared to the speed of light, but there is no gravity (or at least negligible gravity), Special Relativity is a better approximation than Newtonian mechanics and is also used extensively. However, Special Relativity cannot handle gravity; see next item.

(3) For situations in which things move fast enough compared to the speed of light, and gravity is not negligible, General Relativity is used. Also, for situations in which gravity is strong enough, General Relativity has to be used even if nothing is moving fast compared to the speed of light; for example, we have to use General Relativity to study neutron stars, because their gravity is strong enough that Newtonian theory is not a good approximation. For all situations in which quantum effects are negligible, General Relativity is the best current theory we have.

(4) For situations in which quantum effects are not negligible, we know how to add quantum mechanics to the theories in cases #1 and #2 above; this results in ordinary (non-relativistic) quantum mechanics, and quantum field theory, respectively. For all situations that these cases cover (i.e., situations where quantum effects are not negligible, but gravity can be neglected), quantum mechanics and quantum field theory are the best current theories we have. For example, the Standard Model of Particle Physics is based on quantum field theory, which includes Special Relativity.

(5) We do not have a good current theory that combines quantum field theory with General Relativity; one of the primary efforts in theoretical physics today is to come up with a theory of quantum gravity that unifies quantum field theory with General Relativity. String theory is one candidate for a theory of quantum gravity; it gets the most press, but is not the only candidate.

4. Dec 19, 2012

### PAllen

To explain my comment, note that special relativity as a local limit holds in (3)[actually, it holds globally for (3)] and (4) above, and there is, at present, no reason to suspect it doesn't hold locally for (5). Meanwhile, there are, at least, reasonable arguments that either or both of GR and QFT change in some substantial way in the domain of (5) - while SR remains locally valid.

5. Dec 19, 2012

### KeplerJunior

Yes I do think that's what he meant. Specifically he said something along the lines of 'a few years ago Einstein's theory of relativity was shown to not work, it isn't used to explain anything now besides gravity'. This wasn't exactly what he said as i can't remember exactly but it is the general idea of what he said. As i said before he was explaining how science works, specifically how theories are tested and improved.

6. Dec 19, 2012

### Staff: Mentor

You may want to point your teacher to this excellent review:
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

"as of this writing there are no reproducible and generally accepted experiments that are inconsistent with SR, within its domain of applicability"

7. Dec 19, 2012

### KeplerJunior

Right well it seems I either misunderstood him or he was wrong.

8. Dec 19, 2012

### Staff: Mentor

In addition to the excellent review site that DaleSpam linked to, you might want to point out to your teacher that, as I said in my previous post, the Standard Model of Particle Physics is based on quantum field theory, which combines quantum mechanics with Special Relativity. So Special Relativity is used to explain a lot--the Standard Model basically covers *everything* besides gravity.

9. Dec 19, 2012

### TheEtherWind

Don't believe anything about relativity from someone who doesn't at least have a physics bachelors...

10. Dec 19, 2012

### Staff: Mentor

That seems too restrictive. My degree is in Nuclear Engineering, not physics, but (a) I still had to have a basic understanding of relativity for my degree, and (b) I've spent a lot of time on my own studying it, outside of anything required for school or work, so I'm pretty sure I could pass a final exam in any physics undergraduate course dealing with relativity, even though I never took one.

Also, to look at it from the other end, you have to be careful even when reading what people who *do* have physics degrees (even physics professors) say about relativity, particularly in popular presentations as opposed to academic papers. It's hard to take a complex scientific subject and distill it into sound bites for lay people that are both understandable and reasonably accurate, even if you know the subject. So from that point of view your criterion is not restrictive enough.