The x, y, and z planes of the coordinate system. Three dimensional space. You probably met them in high school. I didn’t until college. I crammed them and several of their friends into two short semesters so I could get into physics that next year. Lazy high school student, me.
Given two separate points in space, movement from one to the other takes what? Time. Loosely considered the fourth dimension time isn’t the same though. It has an arrow, an obvious direction or flow. The coordinates system does not. For example, if I show you a video of a dot moving from one of those two earlier points to the other, you wouldn’t be able to tell if the video was going forward or in reverse. The dot could go either way. But shown a video of a glass dropping and shattering on the floor in reverse, you’d know it was backwards. That’s the arrow of time. So while it appears to be the fourth dimension, time really isn’t the same as the previous three.
So what is time? Movement. What’s the difference between a photo and a video? A video shot of a blank wall is no different than a photo of that blank wall. A video records movement, the passing of time, while a photo is just a singular moment in time.
Right now we are hurling along in space at thousands of miles per hour. Not only that, we are expanding. At relatively similar speeds too, which makes our times seem similar. Since time is movement we only know of two things that can alter time; speed (velocity) and mass (gravity). The faster you go or the more massive you are, the slower your time passes relative to others going slower or less massive. Doesn’t take much to make a difference. GPS satellites have to recalculate their onboard clocks to match ours on earth. Experiments on the space station have shown that their distance from earth has a noticeable difference.
What happens though, if we are traveling together at light speed and I push you forward? It is theorized that any extra energy we’d receive at light speed wouldn’t make us faster but more massive. That energy has to go somewhere according to the laws of energy conservation. Since you can’t go faster than light you’d get heavier.
But what if it didn’t?
What if, instead, that push took you somewhere else?
Have you seen the 2003 film 21 Grams? The title comes from a famed (or infamous) study by Dr. Duncan MacDougall. Early in the 20th century he attempted to weigh people at their moment of death to see if the soul had weight. A flawed experiment, the published findings stuck in popular culture. The question is valid. If you believe your soul has energy, it stands to reason it should have weight.
Similar questions surround black holes. Of great mass, not even light can escape its gravitational field. Time is altered near and in black holes, but this is theory. No one has yet volunteered to see one up close. Wouldn't do us much good. Since light can’t escape neither could radio or cell signals, so they couldn’t phone home to clue us in. Maybe a tin can with a really long stretchy string . . .
You take time for granted. So do I. An excellent book for folks with a passing interest in physics is Stephen Hawking’s A Brief History of Time. It is very readable. You might be surprised. You may have questions after you’ve read it.
I certainly did. I discovered that it outsold Madonna’s coffee table book Sex.
There’s hope for humanity yet.