Question

What leads to a scientific theory being revised ?

Answer 1

Discovery of a new phenomenon that cannot be described by the existing theory.
New Experimental evidence suggesting that the theories predictions were incorrect.
Like the one that happened a while back about particles travelling faster than light it created a lot of fuss, people were thinking that Einstein might have been wrong and they might need to revise the theory of relativity but it turned out that their results were incorrect

Answer 2

When the theory fails to adequately explain experimental results.
Classic example of this being experiments with a LINEAR ACCELERATOR in atomic/nuclear/particle physics. The idea was to accelerate charged particles such as electrons or protons to very high speeds, and watch what happened to the and also make them collide with particles and, basically, see "what came out". (If you want to know what's inside something, you can always try breaking it open and having a look.)

On the ideas based on Newtonian (classical) physics, the particles' speeds should be limitless. Just keep giving them more energy, and they'd go faster.

HOWEVER, this is NOT what was observed during experiments with a linear accelerator. It didn't seem to matter HOW MUCH energy was given to the particles, their speed NEVER went beyond the speed of light, nor even equalled it, although it did get quite close (possibly "asymptotically close") to it.
In effect, the particles' masses increased.
This was part of the reason why the idea of "mass-energy" came about, and that Einstein equation E=mc squared.

There were/are many other examples of the failures of Newtonian (ie LOW SPEED) mechanics - another one being the failure to accurately account for the orbit of the planet mercury round the sun.

These sorts of failures are what paved the way of Einstein's theories of relativity (with a lot of help from his wife, Mileva Maric-Einstein) which are the special theory and the general theories.

Answer 3

Great answer dude

Answer 4

^^ if that's directed at me then thanks very much.

Answer 5

don't forget the election of a chump as president :)