Is math subjective?

I was arguing with a friend over whether reality is objective or subjective. He says subjective, because of the double-slit experiment, and that reality changes depending on whether we observe it or not, so it only exists in our minds.

I know this is right.. But something still seems off to me.

This isn't right.

Your friend is wrong about the double-slit experiment and math in black holes. The answer to your question depends entirely on what you mean by "subjective" and "objective" and I'm not sure you know what you mean. So try to tell us what you mean by these terms.

Math is entirely conceptual. What's different in a black hole is PHYSICS, so the math used to describe physics is different, but 2+2 is entirely unaffected by gravitation, however mighty.

In terms of quantum physics I'm a layman so forgive me if this is too simplistic or wrong, but I think I see a couple problems with the way you state it. 1) Once the situation is observed and the state is determined, it doesn't get redetermined differently for different observers. Having an effect on reality is not the same as reality being subjective. 2) Quantum physics doesn't actually care about intelligent "observers". The reason "observing" something influences the state it is in is because at the quantum level you get information about things by how they interact with other things bounced off them, and those things effect the thing being observed. A way of thinking about is if there are a bunch of bottles in a dark room and you can only figure out where they are by throwing a baseball into the room. Each time you hit a bottle, you find out WHERE it was, but it's no longer there because you just shattered it. Until you hit it, you only have a rough idea of its probability of being in any given spot. When you "Observe" it the state of the bottle changes, but it's not something that you did by observing it but by the method you used to gain information about it.

reality changes depending on whether we observe it or not

no. reality changes depending on interactions that happen within reality.

so it only exists in our minds.

even worse. see map and territory. Even if it's in your mind, there is a system that generates predictions and a system that generates observations. They are different.

math is relative depending to where we are. In a black hole, math is different from on earth.

Math is same everywhere. Physics may break down in black holes. Math is constant and objective. Even God can't touch math.

So reality changes... depending on our location

no

but I couldn't exactly find one that fit my question completely.

map and territory (the simple truth). beyond the reach of god. quantum physics sequence.

He says subjective, because of the double-slit experiment, and that reality changes depending on whether we observe it or not, so it only exists in our minds.

Even if that were true, it wouldn't really be a kind of subjectivity that matters. It doesn't give you superpowers, you can't close your eyes and jump off a cliff. If reality actually were subjective, it'd show up in more places than subatomic particles, and he'd have much better evidence.

Suggested reading: the quantum mechanics sequence, and the simple truth.

http://lesswrong.com/lw/r5/the_quantum_physics_sequence/

http://yudkowsky.net/rational/the-simple-truth

Try math is subjectively objective., which explores the issue I think you're trying to raise.

As other commenters have said, with regards to the double-slit experiment and black holes your friend is just wrong.

This sounds like a case of Disputing Definitions to me. Is there anything different about your and your friends model of reality inside a black hole, or your understanding of quantum physics? If not, then there is no dispute, and you're just calling reality different words.

I totally disagree with his conclusion, but here is Eliezer on possible proofs that 2 + 2 doesn't equal 4

Subjective worlds must be causally closed; they cannot transmit information to other worlds since that would break the principle that each world is subjective. As such, there can be no subjective reality: if subjective reality were true, causal closure would demand that your observations about the world are semantically equivalent to a world in which you are alone as an observer.

For example, imagine that we lived in Minecraft, which has a procedurally generated world. We use a seed (say "404") to kick off the algorithm. But say instead that we use a seed and the username of the player. Is World 404 different for each user?

No; there is no "World 404", there is World 404-TheatreAddict and World 404-Hyena and so on. The reason is that the function we use to generate the world takes two variables, seed and username, to work. A world can only be defined by this pair and has no existence independent of it. Naturally, this world is causally closed; my playing does not effect yours, you will never see my buildings nor will you ever send me angry messages about burning down 16 chunks of forest.

While this world is trivially objective, all objections to a subjectivity thesis are trivial because it is trivially untrue or unprovable. Every attempt to prove it will require a condition, like causal closure, which collapses it to a special case of objective reality. The simplest of these is the resolution to the subjective proposition itself, independent of worlds: if everything is subjective, that principle itself is objective.

math is relative depending to where we are. In a black hole, math is different from on earth.

Federal income taxes in the US are relative depending on how much you make. If you make $5,000 a year, people who make $5,000 a year pay no income taxes. But if you make $500,000 a year, people who make $500,000 a year pay ~30% in income taxes.

So you see, the US tax code depends on how much you make.

Unless...unless it's also true that if you make $5,000 a year, people who make $500,000 a year pay ~30% in income taxes, and if you make $500,000 a year, people who make $5,000 a year pay no income taxes. In which case, the US tax code would not depend on how much you make, only how much you pay in taxes would depend on how much you make.

Hmm...