• So Einstein was always right was he?
• Don't physicists just worship Einstein?
• But isn't relativity just a theory?
• Is Special Relativity right?
   
• Are you a physicist?
• Would you be upset if someone really did show Relativity to be wrong?

So Einstein was always right was he?

No, of course not. Two of his biggest errors concerned the random nature of particle decay inherent in Quantum Mechanics (a branch of physics he helped to formulate), and in not realising that the Universe is expanding even though his initial equations said that it should be. However, none of this invalidates Special Relativity.

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Don't physicists just worship Einstein?

Nope. While they appreciate that he made enormous contributions to physics they have no problem at all with saying that he got some things wrong, and saying so firmly. No-one in physics is sacred - Einstein is not a god.

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But isn't relativity just a theory?

In science the word theory has a different meaning to that used in everyday speech or writing. In physics the word theory is usually used to denote a mathematical framework that allows predictions to be made, rather than a hypothetical idea. For example, the Theory of Special Relativity predicts, mathematically, that a clock on a fast aeroplane will slow down, and, most importantly, by how much. Experiments can then be carried out to see if this is true (it turns out that it is - see here). Generally, to attain the status of theory a hypothesis must be backed up with a substantial body of evidence, but this isn't always the case.

Rather than pointlessly dwell on semantics physicists prefer to get on with the science.

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Is Special Relativity right?

In physics nothing, strictly speaking, can be "right" or "proved". The best that can be said is that there is overwhelming experimental or observational evidence that supports a model. In order to be scientific in the first place such models need to be falsifiable; that is testable in some way that could possibly lead to the model being demonstrated to be false. Note that falsifiable does not mean false.

For example, saying that there is a planet in a distant galaxy that is made entirely of undetectable lentil soup is not falsifiable and so not science. There could well be a planet made of lentil soup, even if it's unlikely, but saying it's undetectable means that no experiment or observation can ever be carried out to show evidence for it; the model is not falsifiable.

Special Relativity, on the other hand, is falsifiable. If it makes predictions that are shown through experiment or observation to be false it is wrong, end of story. But no matter how many correct predictions it makes it can never be shown to be "right" because it needs to always be falsifiable to be considered science. Relativity can never be "proved" but the overwhelming experimental evidence means that it is a useful model, both scientifically and practically.

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Are you a physicist?

No. I have degrees in physics and lecture in subjects that either include physics or are branches of physics (such as acoustics) at two universities, but I am not a research physicist.

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Would you be upset if someone really did show Relativity to be wrong?

No! I'd be very excited about it! It would instantly open up a whole new branch of physics and discovery. Besides, relativity is such a useful model that it's unlikely that it would be discarded entirely. This is because as a model relativity is successful and useful.

For example, Newton's Universal Law of Gravitation is wrong. Oh it works well enough providing we keep to relatively low speeds and small masses. It allows us to send rockets to Jupiter and beyond and does so with a very high level of precision, but it's still wrong. Even a rocket travels at a relatively slow speed (compared to the speed of light) and Jupiter, as big as it is, is still a relatively small mass (compared to, say, the Sun).

How do we know Newton's gravity is wrong? There are many examples, but two will do. Firstly, the mass of the Sun (which is nothing special when it comes to stars) distorts space around it. This can be seen during a solar eclipse when stars and the planet Mercury appear in places that they shouldn't according to Newton's gravity. Secondly, according to Newton's gravity, being further away from a mass, such as planet Earth, shouldn't affect the rate at which time passes. However, time does change with distance from a mass, as shown by experiment -- if you are sitting or standing upright your head is aging very slightly faster than your feet^[1]. Both of these phenomena are fully accounted for by Einstein's General Relativity (indeed, they were predicted by General Relativity).

So why not just drop Newton's gravity if it's wrong? The key to the answer is in a previous paragraph - "it works well enough providing we keep to relatively low speeds and small masses". Newton's gravity is much easier to use than Einstein's relativity and it's only very rarely that, on the Earth, we work with systems that require anything other than the former. Even our fastest space probes need to travel many millions of miles before they are off-course by an inch or two due to the differences in the two systems. Newton's gravity is still very useful and more than adequate in almost every situation.

It's likely that even if relativity is overthrown any new model would need to encompass it (General Relativity encompasses, but enhances, Newton's gravity), and even if it's discarded entirely it's been instrumental in allowing many discoveries to be made, just as Newton's gravity did before it (and still does).

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