Write the idea down somewhere. However, ideas are a dime a dozen and are essentially useless unless you have a viable plan of attack. For instance, I would love to work on something world-changing like time-travel, teleportation, or anti-gravity, but there are currently no fruitful ways of even approaching those problems.
I had an advisor tell me that I should always be keeping several "big" problems on the backburners at all times, so that whenever I find out about a new technique or technology, I will be able to immediately think of ways to apply the new tools to the big problems. He said it will fail 99 percent of the time, but on the 1 percent of the time that it does work, everything will somehow fit together and with any luck, you will have found a viable approach.
I had an advisor tell me that I should always be keeping several "big" problems on the backburners at all times, so that whenever I find out about a new technique or technology, I will be able to immediately think of ways to apply the new tools to the big problems. He said it will fail 99 percent of the time, but on the 1 percent of the time that it does work, everything will somehow fit together and with any luck, you will have found a viable approach.