Skip navigation

Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

Do objects really contract when they travel near the speed of light?

By any standard of measurement you wish to define and measure, yes, objects really do contract. The problem is that so long as our measuring process has to do with the movement of light as the fastest messenger, we cannot avoid this problem. Paradoxically, it doesn't mean that the atoms in the moving spacecraft suddenly get compressed in the direction of motion in any absolute sense. The traveling observer will see absolutely nothing occur in the local conditions of their moving platform and the separations of the atoms. The contraction, however, is more than an optical illusion because so far as the physics of the stationary observer are concerned, the length of the traveler along the direction of motion has contracted. The clocks used by the traveler have also slowed down. Allowing the traveler to live LONGER in the stationary observer's reference frame than if he/she were not in motion. These are real, measurable, phenomena. What they mean in any absolute sense is not important. Our intuitions were not designed to include such phenomena and rules of operation!

Return to the Special & General Relativity Questions and Answers page.

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