What is the craziest idea in all of physics?

Sepideh: What is the craziest idea in all of physics?
Also, which idea in physics is the most fun?

Which physics idea is the most beautiful?

This only goes for widely accepted theories/ideas in physics, nothing that has been discredited or has more detractors than proponents.

Answers and Views:

Answer by Civil
Crazy ideas:

1) Quantum tunneling: there’s a particle over here on one side of a barrier. Suddenly its
over there on the other side. But it never traversed the space between!
Proven.

2) Superposition of states: (The universe ‘knows’
when we are watching). Particles exist in a combination of possible quantum states, until they are observed. Observation collapses the
Schrodinger probability wave function, causing the particle to take on one of the possible states.
Theory.

3) Entanglement and non-locality: What happens
to particle “A” over here has an effect on particle
“B”…waaaaay over there. But they are not connected in any way, plus they are too far apart
for any signal to travel between them if they were
somehow connected. Spooky action at a distance?
Proven.

Beautiful ideas:

General Relativity: the way time/space/velocity/geometry
are all inter-related.

String/ M-theory

All personal preference, of course.

Answer by Link
Personally, I’ve always found Einstein’s ideas in general relativity to be the craziest. Cut down to nuts and bolts, Einstein’s general relativity basically says that gravity is the same as the “force” that pushes you back in your car seat when you step on the accelerator. Its a false force that appears because you’re in an accelerated frame and the falling object is really in an inertial frame. So basically objects don’t fall because some invisible force reaches up and pulls on them, they fall because the ground rushes up to meet them. That is why all objects fall at the same rate. “But wait”, I hear you object, “if the ground rushes up to meet the falling objects, then wouldn’t that mean the Earth is expanding? Since all objects everywhere fall and the ground is always rushing up to meet them” Einstein handles this by saying that the spacetime around the Earth is warped and bent and follows non Euclidean geometry. Its an absolutely crazy idea, but I think its incredibly brilliant and beautiful.

The other idea I like is complimentarity from quantum mechanics. Have you ever seen that painting of the old woman/young woman? Here is a link to it: https://2.bp.blogspot.com/_Sky3YbH72kU/R_GlbT-VnuI/AAAAAAAAAUk/ZltTuAbwgfM/s320/Old%2BLady-Young%2BWoman%2BIllusion.jpg Depending on how you look at it, you perceive it to be a painting of either an old woman or a young woman. You might ask yourself, “Which one is it really a painting of?”. Well, the objective thing that is the painting exists independently of our perception of it. This is the idea behind complimentarity. It says that when we ask whether things like light or electrons are really waves or particles, we’re basically asking the same thing as whether the painting is of an old woman or a young woman. The truth is that they’re neither, those are just our ideas and perceptions about the objective things. Crazy stuff. 😀