I'm supposed to study myself but instead I am sharing this exercise with fedi! Let's see what you think.

You are a patent clerk. Because you are lazy you want to reject as many applications as possible without reading the technical details, but instead just based on whether the the idea breaks fundamental physical principles. Choose which ideas are not worth considering and give a short explanation for why.

1) Machine that enables time travel 100 years into the future [H.G. Wells]

2) Hourglass that enables time travel 1 minute into the past [P.O. Persia]

3) Creation of gold from lead [S.D. Weisen]

4) Drying out a cellar with the use of magnetic monopoles [C. Pot]

5) Creation of bread and wine from energy [J.C.S. Star]

I received some very good answers! Here is mine.

1) Going to the future is possible. Not only are you already traveling to the future at a rate of 1 second per second, special relativity allows you to take a path through spacetime where you experience very little passage of time compared to people who take a different path. To travel 100 years into Earth's future, you just need to get into a spaceship and go brrr. Travel close to the speed of light to a random nearby star and then turn back. The closer to the speed of light you are, the shorter the journey feels to you. You can go arbitrarily far into the future arbitrarily quickly (but it requires absurd amounts of energy the higher you go). So, H.G. Well's proposal deserves a proper look!

This is the one I'm most inclined to throw in the trash. At least in special relativity time travel into the past violates causality and is therefore impossible. The story gets more interesting in general relativity. In _principle_, we can imagine something called closed timelike curves, paths through spacetime that form a closed loop. I don't think there is currently any known way to actually construct such a path - it would need to have always existed. And taking the path is not what you would want from time travel: it's just an endless cycle that repeats itself. You wouldn't even be able to remember going through it because your brain gets reset when passing START. It's also highly debatable how this could possibly be compatible with thermodynamics. Sorry P.O. Persia, your application is _extremely_ unlikely to work. I'd take a look anyway because my laziness is weaker than my curiosity, but if this exercise were on a test I'd mark this point as DENIED.

Ah yes, the dream of alchemy. Turns out there's nothing in physics that forbids this! Lead just has 3 more protons than gold. I don't know enough about nuclear physics to comment on how easy it is to remove them, but there certainly is no principle that forbids this. It might be the easiest point to execute on this list. S.D. Weisen, let's see your technical proposal!

Okay this is probably the most interesting one. I have no idea what the deal is with drying out a cellar, but I'm taking the question to be about the existence of magnetic monopoles. As was rightly pointed out, Maxwell's equations say that there are no magnetic sources, which would make this application dismissable. But! Maxwell's equations are not actually the end-all-be-all in physics! The equation that denies monopoles is, if I recall correctly, not based on some _principle_ but on _observation_. We don't see any monopoles so Maxwell set the source term to zero. Not only are monopoles possible, many physicists _expect_ them! Grand Unified Theores (theories which try to unify the three forces [not gravity] at high energies) usually predict magnetic monopoles to exist, namely in the form of topological defects. I don't know the details right now and this topic deserves its own thread someday, so I'll leave it at that. But note that since they are topological defects and not excitations of some particle field, these monopoles can not be created or destroyed. The prediction is that there were many many monopoles in the universe, but the inflationary epoch of (which is itself debatable) expanded the universe so drastically that all those monopoles have been hopelessly diluted. While other particles were continually created during inflation monopoles were not. I think I heard that according to some rough estimation there may exist just one magnetic monopole in the observable universe. So, C. Pot, if by some miracle you found it then I really want to see it! But I'd also urge you to donate it to science instead of using it to... dry out cellars? I also don't see how your business would be able to scale with such a limited quantity.

Okay, so you want to create bread and wine from energy. "Energy" is a bit non-specific but I'll let it slide. I see no hindrance in principle! Physics' most famous equation already gives us the relationship between matter and energy. However, the cost to create a loaf of bread and a bottle of wine is immense. With the current energy prices, are you sure that's the best way to stay fed during the winter? But that's the problem of your business, J.C.S. Star, not mine. Let's give the application a thorough look!

@pseudoriemann >However, the cost to create a loaf of bread and a bottle of wine is immense.

Two brainlet questions for you:

1: Is the energy cost of that much matter absolute?
2: Am I correct in assuming that it would be far more feasable to use energy to power processes that "construct" the bread and wine from some kind of nebulous "source matter"?