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I put “time travel” in quotes in the title for a reason. To clarify, you and I are traveling at the speed of time right now. Time is moving “forward,” and we’re moving forward with it. The place is always here, and the time is always now. But that’s not usually what we mean by time travel. In the title, I’m specifically referring to traveling into the past or into the future. And it’s not possible. I’ll prove it.
First, let’s consider leaving now, and traveling into the past. Let’s say you wanted to go back in time six months and stand on the observation deck of the Empire State Building in New York. So you build a time machine and travel back in time six months.
But there’s a problem. Six months ago, Earth was half an orbit away, on the other side of the sun.
But there’s another problem. The sun is traveling in a curved path, and it was a long way from here six months ago.
But there’s another problem. The sun holds a certain gravitational position in the Milky Way galaxy, which is traveling on a curved path, and the Milky Way was a long way from here six months ago.
But there’s another problem. The Milky Way is part of a cluster of galaxies called the Local Group. The Local Group is traveling on a curved path, and the Local Group is a long way from where it was six months ago.