"Yes, we know that GR is not a quantum theory and has to be modified. It also works whenever we have tested it. We need QM because it works when we investigate small things. We need GR when we investigate very massive things. It isn't very common that both come up in the same situation, so we have no way to test any of our proposed quantum theories of gravity."<quoted text>Yes, we know that GR is not a quantum theory and has to be modified. It also works whenever we have tested it. We need QM because it works when we investigate small things. We need GR when we investigate very massive things. It isn't very common that both come up in the same situation, so we have no way to test any of our proposed quantum theories of gravity.
If anyone finds a case where all or part of a scientific theory is false, then that theory is either changed or thrown out."
And the changes can be as minor as adding additional assumptions. For example, a couple hundred years ago, Newton's laws were not working with the orbit of the planet Uranus. So they had to be 'modified or changed'. In that case, the change was to add an additional planet. In that way Neptune was discovered. Notice that the basic theory of gravity was itself not 'modified or changed', only the particular assumptions for that specific situation.
And that is how science works. When observations do not agree with theory, we first see if we have missed something in the environment and include it in the theory. This alone can be a very tricky thing. it is only after that when the basic theory is modified. Often this consists of minor changes. And after repeated attempts at minor changes have failed, it is only then that we change the overall theory.
[QUOTE]A scientific theory in one branch of science must hold true in all of the other branches of science."
Although often the conclusions are irrelevant. For example, the theory of tectonic plates in geology has no bearing on quantum mechanics. For that matter, general relativity has no bearing on quantum mechanics in any case where we have actually been able to measure. That is why both are still used.
A theory must work everywhere in the universe. We can't have two everywheres can we?
"S. JAMES GATES, JR.: The laws of nature are supposed to apply everywhere. So if Einstein's laws are supposed to apply everywhere, and the laws of quantum mechanics are supposed to apply everywhere, well you can't have two separate everywheres."
"Although often the conclusions are irrelevant"
While this maybe true it's not the situation with QM and GR.
those have huge issues with each other.
"BRIAN GREENE: It's a little known secret but for more than half a century a dark cloud has been looming over modern science. Here's the problem: our understanding of the universe is based on two separate theories. One is Einstein's general theory of relativityâthat's a way of understanding the biggest things in the universe, things like stars and galaxies. But the littlest things in the universe, atoms and subatomic particles, play by an entirely different set of rules called, "quantum Mechanics"
These two sets of rules are each incredibly accurate in their own domain but whenever we try to combine them, to solve some of the deepest mysteries in the universe, disaster strikes."