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IgorPartola ◴[] No.41895504[source]
If I understand correctly, we experience time at nearly the speed of light. What I mean by that is that any particle’s 4 dimensional velocity vector has the magnitude of c which means that if it is mostly at rest in space then time has to be the major contributing factor but the magnitude of the vector. On the other hand something like a photon experiences to time at all as it moves through the 3 space dimensions at a total of c.
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crdrost ◴[] No.41897752[source]
You have understood it about as well as the article did!

Now, there is a huge nuance here, which is that you are moving near the speed of light, to certain observers. This is like the whole "relativ-" prefix in "relativity", you are at rest in your rest frame, you are moving very fast in some other rest frames. The cosmic muon crashing into Earth, sees you as time-dilated! So with that nuance "we experience time at nearly the speed of light" just becomes kind of a tautology like "we experience time how we experience time."

But a better way to think about this is, you are about two meters high, you are about a meter wide, about a half-meter dorsoventrally... and about 30 000 000 m in the other direction, if we're looking at the human reaction time/blink-of-an-eye range of 0.1s (think about how 10fps video is at the cusp of being continuous and how 20Hz is where clicks stop sounding differentiated and instead start sounding like a bass note).

What this means is that if we look at you relativistically, you kind of look like a big "rope" with worldlines of other atoms coming in, braiding into your body, eventually leaving... but the strands of this rope are bundled into these cells that have worldlines over 99.9999% parallel. (Atoms within those cells move faster, but you're probably at least 99.999% parallel even if we make that statement?) And that astonishing parallelism is precisely why relativity is not very intuitively plausible to us.

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1. ByThyGrace ◴[] No.41898399[source]
> and about 30 000 000 m in the other direction, if we're looking at the human reaction time/blink-of-an-eye range of 0.1s

So: distance over time, but is the time dimension only measurable in distance over time? Is there a purely time unit, or does that not make sense when speaking of spacetime?

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2. crdrost ◴[] No.41901603[source]
Yeah normal time units still exist in relativity, clocks gotta clock.

But ratber it's that there exists an operation which is almost entirely like rotation, but it rotates x, y, or z into w=ct, where w is measured in meters just like x,y,z are, but t is measured in time units, and c is the speed of light converting between them. Instead of a rotation's formula with sines and cosines like

    x' = x cos θ + y sin θ
    y' = y cos θ – x sin θ
    (x')² + (y')² = x² + y²
relativity has a slightly different set of functions sinh and cosh that are very closely related to sin and cos. (Sine and cosine have Taylor series where the polynomials alternate, sin(x) = x – x³/6 + x^5/120 – ..., and sinh and cosh have the exact same Taylor series with all + signs rather than alternating + – + –.) The analogous expressions are then,

    w' = w cosh φ — x sinh φ
    x' = x cosh φ — w sinh φ
    (w')² – (x')² = w² – x².
This transformation, in relativity, is just built into how any acceleration works. So whenever you accelerate, even in pre-relativistic physics, you expect to see the emergence of some Doppler shifts. In relativity these shifts are not quite as strong as expected from the classical theory, and as a result when you subtract off the Doppler shifts and try to say "what has happened" you get an answer that "the meaning of the present moment, which historically defined a 3D universe frozen at a point in time, identifies a different 3D slice of the 4D spacetime." And this is what "rotates", it's the rotation of the plane that you think is the "present moment".

The fact that you are discretely "you" about ten times per second, I am taking as a fact of biology. But if you try to convert that biology into physics, that's where you convert t into w to get that t=0.1s converts to w = 30,000 km.