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What is the difference between scientific theory and scientific law?

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February 14, 2011 9:27AM

The short answer to this is 'nothing'.

Here's a longer answer: science is all about applying what's known as the 'scientific method'. We observe something in the world around us and question why that thing may be - this can cover anything, from why water is wet, why things fall, why dinosaurs went extinct - anything at all. We then try to come up with an explanation that seems to fit what we're observing - if our explanation manages to do this, it becomes our theory for this thing. For example, the Big Bang Theory gives us an explanation that fits our observation that the universe is expanding. But we don't leave it at that. We have to test our theory - if we observe the same thing in a different way, does the theory still hold? If the answer is 'yes', the theory becomes stronger and more trusted; if not, the theory becomes weaker - we've confined the area in which it works, and we may have shown that it isn't true at all and needs to be discarded.

A theory becomes a law when it has passed a series of these tests and seems to be correct over a wide range of looking at things, and is therefore accepted as being a good description of reality. But this is highly subjective - there's no set number that suddenly turns a theory into a law; it's more how the scientific community as a whole views the theory. This subjectivity can be influenced by many things: age (older theories tended to become called Laws sooner the newer theories), simplicity (an easy-to-understand equation will be come accepted faster than a big, complicated one), or just simply the zeitgeist (If a theory fits easily in with what people just believe to be right, it will get accepted faster).

One final example to show that the naming is pretty much subjective: Newton's Laws of Motion, which fitted most observations for a good couple of hundred years, but at the beginning of the 20th century, they were superseded by Einstein's General Theory of Relativity; in this case, the 'Theory' is scientifically stronger than the 'Laws'.