Science Buddies: "Ask an Expert"

If someone is traveling to the Andromeda Galaxy at near-light speed and we are video calling them from Earth, how would they appear to us, and how would we appear to them? Would their movements seem slow to us, and would our movements seem fast to them? Since the video signal itself is also affected by relativity, how would that impact what each side sees in real time?

Hello!

This is a really interesting question. If someone were traveling to the Andromeda Galaxy at near-light speed and video calling us, they would appear to move in slow motion due to time dilation. From their perspective, we would look like we were moving very fast. Since the video signal is also affected by relativity, it would be delayed and stretched, making real-time communication nearly impossible. The farther they travel, the greater the delay, and eventually, the signal might take millions of years to reach either side! This was really fun to figure out, and i really think you should try to push it a bit farther if your interested.