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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

If you slowed down light, would it become less of a wave and more of a particle?

No, because light has no rest mass, which means that it can never be slowed down to become a physical particle with a non-zero mass like an electron. Instead, if one could ever imagine slowing light down, an impossible technological accomplishment I might add, it would simply vanish altogether. Light has only one state of existence, and that is to travel at exactly its normal speed. Without rest mass, it has no existence at slower speeds.

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.