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Originally posted by Wednesday:
1. If the universe is expanding, which direction is the center (from which we are expanding) in? Can we as objects travel to that center?
You're thinking three dimensionally. The center of the 'explosion' would be meaningful in regards to the universe's 4-D "shape." As it is, however, nobody knows the "shape" of the universe, and the cosmic background radiation (an 'echo' or sorts from the big bang) is uniform throughout the cosmos. The evidance for the expansion of the universe lies in the fact that everything (within logical reasoning) is moving away from everything else (like here, because then you must account for attractive forces and stuff). As things stand right now, it is not possible for science to detect a 'center' to the universe.
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2. I understand why the sky is blue, but why are sunsets red and orange?
When the sun is above the horizon, there is little atmosphere for the light to travel through. As it sets and rises, however, the angle of light passes through a substantially larger amount of atmosphere. The particles in the atmosphere block the shorter light wavelegnths of light and only the longer wavelegnths like orange and red can pass through virtually unaffected. The same effect can be seen where there is lots of air pollution, such as with a large fire. Last year during the Hayman fire, I got some spectacular pictures of a blood-red sun at noon. The shorter light was bounced about by the particles in the air.

It's basically the same principals as why the sky is blue.
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3. Why is it easy to stay on a bike while moving, but impossible once it stops?
The gyroscopic tendacies of the wheel spinning keep it upright. It takes less energy for the wheel to spin at a tangent to the ground than at an angle (friction would compound the energy lost). Once it stops, there is no more energy being used and it is a stationary system. There is no energy counteracting the pull of gravity, so gravity wins. So, with a moving wheel, it is simple to stay upright because it uses the least amount of energy, but when the wheel is not moving anymore, it tries to go to the most stable position where the center of mass is closest to the ground -thus falls, with or without you on it.