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Comment by mrfusion | Hacker News Reader

Are we flat in the time dimension? Or what is our time size?

It’s something of a philosophical question. We tend to think of distant galaxy’s as if we are viewing them via some FTL means with a single consistent now. NASA for example tracks distant Mars probes like that rather than marking timing based on when the signal was received.

Alternatively, you can think of everything that could impact you as something of a now light cone. The second view has the universe existing as a 3D surface in 4D space time which means objects have a temporal width for each observer. That can be a really useful mathematical model.

PS: Edited the above several times for clarity.

I’m reminded of the film Donnie Darko, but I won’t say more as to not spoil anything for anyone.

> The creatures can see where each star has been and where it is going, so that the heavens are filled with rarefied, luminous spaghetti. And Tralfamadorians don’t see human beings as two-legged creatures, either. They see them as great millepedes—“with babies’ legs at one end and old people’s legs at the other,” says Billy Pilgrim.

—Kurt Vonnegut, Slaughterhouse-Five

Interesting way to phrase the question, the answer is... depends on relative motion. The notion of simultaneity which is the technical term for what you describe as "being flat" in the time-direction is not an absolute thing in relativity. With respect to your own reference system you are essentially "flat" in the time direction [1], but with respect to someone that moves at a certain speed with respect to you you have certain size in the time direction.

The best way to picture it is via Minkowski diagrams, you can find some neat visualizations in the wikipedia article: https://en.wikipedia.org/wiki/Relativity_of_simultaneity

Simply picture an extended object in the x direction, Lorentz transformations are going to rotate it slightly in the time direction causing it to become extended in the time direction.

[1] If you take it to the extreme you may consider that different parts of your body move with respect to each other and thus they are not in the same reference frame. In which case, not even with respect to yourself are totally "flat" in the time direction.

If you're walking at 1 meter per second with a 1 meter stride. The space-time interval between your footsteps is: sqrt( (299,792,458m)^2 - 1m^2))

299,792,458m is for the distance traveled by light in one second. The -1m is for the distance between your feet.

"All tragedies are finished by a death, all comedies by a marriage." —Lord Byron

>Or what is our time size?

That's just another way of describing the total time you exist.

Your size in X, Y, Z isn't equal to the total distance you've traveled, so why would your size in t be the total time you've traveled?

your size in X, Y, Z, is how much space you occupy at once, i.e., at a fixed point on the time axis. But how would we even make sense of the notion of "size" on the time axis? How much time we take up for a fixed value in one or more of the X, Y, and Z axes?

If you consider your body has extent in time, then when you move between two points in space, your body is a long worm connecting those two points. So your size in some way is related to the distance you travel in your life. But even without time, a person's size isn't really well defined anyway. Is a person wider if he stretches his arms out sideways?

We don’t know, because we don’t know if the past or future are objectively real, or if we ride the wave so to speak.

Eh, that view doesn't make sense since every particle has it's own light cone, hence it's own time cone.

PBS spacetime did an episode about this recently.

Does it exist earlier or later in the time cone ‘already’?

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