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Q & A: seeing yourself from behind

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Most recent answer: 06/28/2013
Q:
Hello there. I have a question: If i will run very fast, close to the speed of light, but in a circle, will i be able to see myself from the back? and a similar question: If i rotate a phone fast enough in a circular motion, close to the speed of light, will the phone be able to take a picture of itself? thank you :)
- Jonathan (age 25)
hungary
A:

This idea can't work in an ordinary area without unusual gravity. Here spacetime is nearly flat, so there is no path with a shorter interval than the one the light follows to get from where it starts to where it ends. That is it takes you longer to get to where the light has been than it takes the light to get there. 

In the presence of very strong gravitational effects, spacetime isn't nearly flat, so strange things can happen even if you don't chase your own tail. If there were something very massive nearby, say a black hole, the light might swing around it and come back to intersect your path. So you'd see yourself. without any mirror. I think that if you were facing so that you'd see your face, the image wouldn't show the inversion that you see with mirrors, where it looks like your handedness has switched.

It's possible that the universe as a whole wraps around on itself. In principle if that's the case, someone could see themselves as the light returned. The time for it to return would have to be tens of billions of years, at least. So it's not exactly practical.

Mike W.


(published on 06/28/2013)

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