Physics has come a long way. But for every advance it makes, it is confronted by a new intellectual opponent. Here are some of the problems and unsolved quandaries vexing even the best minds of our generation.
Why does it appear that time only points in one direction? Physics should have no problem with time also running in reverse, though scientists have tried to explain this away by pointing to nature's urge towards entropy or chaos. One relatively new theory deals with gravity and spacetime, and how a single gravitational moment always and necessarily leads to two distinct, opposing futures that can't be reconciled. But another theory seeks to have that arrow point in both directions, making the universe eternal.
If a black hole is strong enough to pull in surrounding information on how it formed passed the event horizon (the point of no return), then how is there information radiating from it that indicates what just happened? Quantum mechanics states that information must be conserved ”” so what's the deal? One theory is that the information gets copied, and then radiates out. Stephen Hawking, who helped complicate the paradox, now has another theory that when particles are sucked into the black hole, they leave behind a kind of 2D holographic footprint; on top of that, he thinks black holes aren't nearly as black and fatal as they were once believed to be.
Vacuums, as predicted by quantum field theory, should have exceptionally high densities, the consequence of which would be large gravitational pulls ”” via general relativity. The only problem is that when this theory is attempted in practice, it yields results that are, shall we say, not to experimenters' liking: their gravitational pull is not there. In fact, the discrepancy measures as much as one hundred orders of magnitude ”” a big difference.
Let's go back to the Big Bang. The microwave background of our universe is relatively homogeneous throughout, and its attributes are somewhat constant. An event horizon is where one region of the universe is separated from another, so much so that they're not in contact with each other, and therefore can't share their attributes. But why, then, is the universe so uniform throughout?
Baryon asymmetry is another way of saying the imbalance of matter to antimatter that populates our universe. Antimatter is just the product of the flipping or switching of every property of matter, and the stuff came about during the Big Bang like everything else. The only problem is we'd expect to see much more antimatter than we actually do ”” and in fact, we have virtually none from the time of inception. What's going on?
The Standard Model of particle physics is generally accepted as the bible for anyone studying the nature of the universe. However, it is not complete. Physicists have attempted to bridge some of the gaps by introducing an ancillary theory of supersymmetry, that predicts the exact opposite of every particle outlined in the Standard Model. They hope that the supersymmetry theory will solve one giant problem for Standard Model proponents: the idea that tiny particles don't have mass, a weird thought indeed.
Zero point energy refers to the energy intrinsic to a system even when that system has been cooled to absolute zero. What's going on there? It's believed that the universe might have a zero point energy, and this is due to the fabric that makes up the universe. Some physicists want to identify this number as the cosmological constant. Others aren't even sure if it's real.
Comparing the size of the smallest possible black hole (gravitational) to the mass of W or Z particles (nuclear force vehicles), the difference is something like 10 trillion times. Gravity is an extraordinary strong force compared to nuclear. The question riddling physicists is: Where did that difference come from? This is known as the hierarchy problem.
Quantum physicists are almost all in agreement that the thorniest subject is gravity, because it is not consistent with the rules of quantum theory. In attempting to reconcile the two, quantum physicists have tried to revise theories of gravity through quantum frameworks, giving rise to very strange theories like String Theory and more.
Invoked and named by Einstein, Mach's principle conjectures that local physical laws are governed by the movements and superstructures of the universe distant and remote. The problems that arise, then, are how does something very far away practically effect something very close? The Wave Structure of Matter attempts to solve this conundrum with in and out waves that can stretch long distances, but is that really the solution?
If there's positive, it stands to reason that there should also be negative, yeah? That's sort of what's posited by physicists in negative mass, which is just a negative sign in front of a numerical value of mass. Though negative mass wouldn't contravene the laws of conservation of mass or energy, it does pose some major problems for the General Theory of Relativity (GR), and so is often rejected out of hand by GR hardliners. Recent physicists believe that they have proven that negative mass can come about...if the conditions for its production are just right. When positive and negative mass come together, well, you just better watch out.
When the momentum of an object is compared to its mass, the result is always a straight line with a slope (rate of change) of about 2. Now, this is held pretty constant throughout the universe, and it's been taken for granted. But no one seems to know just why.
A mass by any other name would be just as forceful. Inertial mass and gravitational mass are two different ways of measuring the mass of something, the former Newtonian and the latter Einsteinien. The problem is that though the equations and methods for measuring are different, there's no difference in the answers produced. That's funny. So how are these two separate equations yielding the same solution?
Deep into the universe is a lot of stuff moving very rapidly very far away, and no one can seem to explain why. The distribution of the matter in this "dark flow" of stuff is so at odds with how the rest of the universe is composed that it poses an intensely difficult problem for astrophysicists. The other thing is, scientists are still not sure if the stuff is going away...or coming straight at us.