Is light a particle or a wave? Is metal a good heat shield? Is the reason that nothing can go faster than light because we have not tried hard enough? Is there any difference between antimatter, dark matter, dark energy, and degenerate matter?

Is light a particle or a wave? Sort of both.

Is metal a good heat shield? Yes.

Is the reason that nothing can go faster than light because we have not tried hard enough? No.

Is there any difference between antimatter, dark matter, dark energy, and degenerate matter? ...Yes, there is.

Explanation:

magnitude and direction

i think it because equal matrices have equal dimensions, only square matrices can be symmetric. for all indices and . every square diagonal matrix is symmetric, since all off-diagonal elements are zero. in linear algebra, a real symmetric matrix represents a self-adjoint operator over a real inner product space.