I’ve seen a lot of physics videos and a friend tried to explain to my brain can’t understand why time is just a perception.
In: Physics
Time does exist, but not in the capacity that we measure it. The way we measure time is something humans just made up.
Time also passes differently based on where you are in the universe. In a place with a great deal of gravity, like near a massive black home, for instance, time passes faster than somewhere with less gravity.
Time is real. When people say time isn’t real it’s just something hippies say. We can measure it, but the way we measure it something we made up.
This is around the point where physics goes beyond our intuition, so it’s where a lot of us get tripped up.
So it is tied up with relativity and the speed of light.
The speed of light in a vacuum is a constant, c, somewhere around like 300 ~~trillion~~ million ~~miles~~ meters per ~~hour~~ second, ~~give or take a few orders of magnitude~~ (the original thing I remembered was off by about 6 orders of magnitude, which is generally considered more than “a few”). Either way, this is a *constant*, and that makes light behave *strangely* compared to other things we’re used to.
To look at this, take the example of shooting a nerf dart out of a moving vehicle. If you’re driving forward at, say, 25mph, and you have a supercharged nerf gun that is not at all safe that fires nerf darts at 25 mph, and you fire the nerf dart out of the car in the same direction as the car is moving, the nerf dart will be moving at 50mph (barring air resistance, etc). Conversely, if you shoot the same nerf gun facing the back/behind the car, the dart will have a net speed of 0 mph.
This is how most objects operate. This is not how light works.
If we take a similar example and (ignore a few laws of physics for a bit): if we have a spaceship that can travel at exactly the speed of light (impossible in reality, but we can pretend for this example), and we take a flashlight and turn it on facing the direction of travel, given the example above we might expect that the speeds would combine, and the light from your flashlight would move at 2 times c. But it won’t. It will move at c.
Similarly, if you point it backwards, the velocity of the light won’t be canceled by your exactly identical velocity in the opposite direction, the light will still travel at c in that direction.
Further, unlike other velocities that are all relative to where we’re observing them from (ex: if you throw a beach ball vertically in that spaceship (or out of it) it will be moving at 0mph to you, but to others watching from a relatively stationary viewpoint, it will be moving quite a bit faster), the speed of light is the same *no matter your frame of reference*.
What this necessarily means is that as you go fast enough to be a significant fraction of the speed of light, time will slow down for you compared to where you’re being observed from.
Again: This is not how we generally experience reality, but we’ve done experiments with atomic clocks that have confirmed Einstein’s findings.
EDIT: unit confusion in the speed of light because I’m old and American. Thank you for the correction.
You may be thinking of Einstein’s use of the phrase “For us believing physicists, the distinction between past, present and future is only a stubbornly persistent illusion.” What he means is that all of space time – from the big bang to however things “end” – exists fully and completely all at once. Things don’t “come into being” in the future or recede into the past – that’s just an illusion. All of it exists right now, has since the beginning of space time, and never goes away. We just “travel” through it, and it is only our experience that makes it seem as if there’s a difference between past and future, and hence an experience of “time.”
Think of the entirety of spacetime as being a giant loaf of bread – at one crust slice is the start of spacetime, and the other crust slice is the end of spacetime. But the entire loaf exists all at once and came out of the oven fully baked – it’s not changing at all. Imagine a tiny ant starting at the beginning crust and eating it’s way through in a straight line from one end to the other. It can’t back up and it can’t change it’s pace. It can only move steadily forward and with each bite it can only get sensory input from the part of the loaf it’s sensory organs are touching. To the ant, it seems that each moment is unique, and while it may remember the moments from behind it, it hasn’t yet experienced the moments to come. It seems there’s a difference in the past and future, but the loaf is already there on both ends. Now what makes it weirder is that the ant itself is baked into the loaf from start to finish so in a sense it’s merely “occupying” a new version of itself from one moment to the next. This also isn’t quite right, since it’s more accurate to say that the ant is a collection of all the separate moments the ant experiences. It’s not an individual creature making it’s way from one end to the other – it’s the entire “history” of the creature from start to finish.
Conceptually difficult to grasp with our limited minds, and this has serious repercussions for the concept of free will, but those are different subjects for different discussions.
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