unsolved questions in physicsWhat, in your opinion, is the greatest unsolved question in physics?

Physics is about figuring out the basic framework of the universe, and there's no way around the fact that a lot of the universe is still a great mystery. So which one of these mysteries would you like solved the most? And, arguably more important, do you think there is any way to solve them?
oh god..there are about a million of those 90% of which i'm quite sure science will never be able to provide explanation to.
lets see..
1-the big bang..the moment when it all started.
2-What was there before that?
3-Where did the singularity come from?
4-Where did human life come from?Are we just
another form of artificial intelligence?
5-Who controls us and what is the purpose of
this messed up thing called life.
light is number one.Magnetism is number two in that order......etc...

unsolved questions in physics
The nature of gravity is a biggie.
Well, the greatest unsolved (and arguably unsolvable) problem
in physics and any other scientific discipline would be "Is there
are God and if so why won't he use easier formulas..."

Beyond that, in physics, I would guess it would be trying to
understand how the 4 different fundamental forces work
with each other - in particular, how gravity fits in.

There's a lot of work going on in string physics which produced
some really cool models but seems, as of now, to be
unprovable. Maybe "Do superstrings exist" would be the
name of that problem.

And of course, physicists and astronomers agree: How did
it all begin? What came before the big bang?
What is reality? If the human race survives long enough I think it will be possible to learnunsolved questions in physics.
Time travel is probably the greatest riddle. The whole Grandmother paradox opens up the possiblity of parallel universes. I would like to believe I am where I am meant to be, but parallel universes would mean my life is just based on a variants and that there is no "correct path" and that I may not be living the best life possible. And if time travel exists, then can we go back and undo past mistakes? The mind boggles.
How the World Trade Centers fell at free fall speed if they wern't helped out by explosives.
the true pi
Finding a unified field theory. It's the Holy Grail of physics.

And of course we can solve the problem. There is a solution, and though it may take us centuries to do so, we will find it.
Why did the chicken cross the road? I'm stumped.