Category Archives: Relativity

Q: What’s it like when you travel at the speed of light?

Physicist: From a classical (Newtonian) view point this is a completely solid question.  However, in the context of special relativity the question itself is (unfortunately) non-sense.  For many practical purposes, the speed of light (hereafter I’ll call it “C”) is … Continue reading

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

Q: Why does going fast or being lower make time slow down?

Physicist: Back in the day, Galileo came up with the “Galilean Equivalence Principle” (GEP) which states that all the laws of physics work exactly the same, regardless of how fast you’re moving, or indeed whether or not you’re moving.  (Acceleration … Continue reading

Posted in -- By the Physicist, Physics, Relativity | 109 Comments

Q: Have aliens ever visited Earth?

Physicist: No. Space is big.  The distances involved are ridiculous, the energies are ludicrous, the costs are somethingelseous.  The New Horizons probe (due to reach Pluto in 2015) is the fastest vehicle ever created.  At its top speed of 16.26 km/s … Continue reading

Posted in -- By the Mathematician, -- By the Physicist, Astronomy, Physics, Relativity | 45 Comments

Q: How far away is the edge of the universe?

Physicist: If you ever hear a physicist talking about “the edge of the universe”, what they probably mean is “the edge of the visible universe”.  The oldest light (from the most distant sources) is around 15 billion years old.  Through … Continue reading

Posted in -- By the Physicist, Astronomy, Physics, Relativity | 79 Comments

Q: How/Why are Quantum Mechanics and Relativity incompatible?

Physicist: Quantum Mechanics (QM) and relativity are both 100% accurate, so far as we have been able to measure (and our measurements are really, really good).  The incompatibility shows up when both QM effects and relativistic effects are large enough … Continue reading

Posted in -- By the Physicist, Entropy/Information, Physics, Quantum Theory, Relativity | 33 Comments

Q: What is time?

Physicist: All philosophy aside, the best answer is due to Einstein, who said (after lots of thought) that “Time is what clocks measure”. The term “spacetime” gets bandied about a lot.  And you may have been lead to (correctly) suspect … Continue reading

Posted in -- By the Physicist, Philosophical, Physics, Relativity | 11 Comments