Category Archives: Relativity

Q: If time is relative, then how can we talk about how old the universe is?

Physicist: One of the most profound insights ever made by peoplekind is that time is relative.  This isn’t some abstract idea, mistake, or mathematical artifact.  If you have two identically functioning clocks, you can start them together, move them to … Continue reading

Posted in -- By the Physicist, Astronomy, Physics, Relativity | 16 Comments

Q: How can something have different amounts of energy from different points of view?

The original question was: … in a scenario with two cars driving towards each other, the system could be measured externally to have an energy equal to the sum of the kinetic energy in the two cars. However, if you … Continue reading

Posted in -- By the Physicist, Physics, Relativity | 29 Comments

Q: Are some colors of light impossible? Can any color of light be made?

Physicist: Just so we can talk about this using physics rather than poetry, for the sake of this article “color” really means “frequency”.  Light frequency is a bit more objective than color and includes things we can’t see (like ultraviolet). … Continue reading

Posted in -- By the Physicist, Physics, Quantum Theory, Relativity | 9 Comments

Q: What is dark energy?

Physicist: The universe is expanding and the rate of that expansion is accelerating.  If the universe were full of only matter (both regular and dark) and energy, then we’d expect that the expansion would be slowing.  Dark energy is the … Continue reading

Posted in -- By the Physicist, Astronomy, Physics, Relativity | 28 Comments

Q: Is geocentrism really so wrong? Is the Sun being at the “center” (i.e. the Earth orbiting the Sun) just an arbitrary reference frame decision, and no more true than the Earth being at the center?

Physicist: When you walk around in this big crazy world, there aren’t any immediate reasons to suspect that the ground under your feet is doing anything more than sitting perfectly still (ring of fire notwithstanding).  Given that, when you look … Continue reading

Posted in -- By the Physicist, Astronomy, Experiments, Physics, Relativity | 13 Comments

Q: Since the Earth is spinning and orbiting and whatnot, are we experiencing time wrong because of time dilation?

Physicist: A little! The movement of Earth, as well as the Earth’s gravity, change how much time we experience compared to other objects in the universe.  If we were to occasionally compare our clocks to clocks in tight orbits around … Continue reading

Posted in -- By the Physicist, Astronomy, Relativity | 22 Comments