Special & General Relativity Questions and Answers
What does the word 'spacetime' mean?
It means that in our universe, 3-dimensional space and time form a single indivisible new physical object which has 4 dimensions. All physical laws and phenomena seem to require thinking about space and time as this blended object. That's what Einstein's relativity theories were all about.
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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.