What would you change? Why?

I would make the quantum foam unstable enough to cause wormholes big enough to cause damage to the universe.
For teh lulz.

Today sure is an exciting day for the Off-Topic Chat.

Physics altercations? Hrm. I would prefer if I could alter gravity to make only slightly less intense than it is. T'would make construction a bit easier.

Also, would these changes happen and everyone would notice, or would people think that it was this way since the dawn of time?

Make it so that I can change the gravitational pull and orientation of an object. Want a car to be the center of gravity in a neighborhood? Why not! Want that car to float off into space? Sure!

It would be immediate and in real time, but you can't go back. So if you made the car the center of gravity for a neighborhood, it would take a little more than just reversing it to fix it. Loopholes would come into play.

I imagine the gravity shenanigans like Dave's time shenanigans in Homestuck. Creating infinite loopholes to make stability.
Maybe I could make magic time holes with my supergravity powers!

Nothing, I like being alive thanks

In theory you could cause an atom to have so much gravitational force it would punch a hole in space-time.

Of course this would be very dangerous.

And fun.

Changing broad aspects of physics throughout the universe sounds like you'd wind up breaking something important (like the suitability of earth to harbor life as we know it) if you did anything noticeable.
I think I'd pass on the opportunity.

But if I did want to break everything, suddenly giving all neutrinos the mass of a super massive black hole would do the trick pretty well I'd think.

i would make gravity as powerful as strong force, because ♥♥♥♥ life

That is quite a negative view you have there Urch.

Urch gets the idea.

Giving protons, electrons and neutrons the same charge would be pretty fun (and increasing the strength of the electromagnetic forces if necessary), the resulting separation and breaking of everything would be pretty impressive.
Or maybe increasing the repulsive forces between electrons so no atoms could bond at all. That or somehow making all matter into H and O2 and watching the subsequent explosion of everything ever, that'd probably be pretty neat too.
Or was the aim to come out of this alive?

well bad boy, it sounds like what you have there is a severe case of chemistry. this thread was about physics, though.

Well, technically, that comes down to a physical interaction, too. I don't think it's exactly missing the spirit of the thread.
If I could change one aspect of physics, it would be to make some material a superconductor at room temperature. That would solve a lot of issues.

I would become the god out of the machine, and rule my planet with benevolence.
(I would use physics magic to become one with technology)