delta t and differential t

[AntonioLao]

[math]\\Delta t[/math] is t2-t1 such that [math]t_1 \neq t_2[/math] .For positive time, t2>t1. For negative time, [math]t_1>t_2[/math], which is not distinguishable for a unidirectional universe.

Differential time [math]dt[/math] is [math]t+\\Delta t[/math] or [math]t-\\Delta t[/math] such that [math]\\Delta t \\rightarrow 0 [/math]. For a principle of continuity, this limit must exist. This is possible if t is an infinitesimal increment of time.

[math]\\Delta t[/math] is always suitable for any quantization formalism, e.g., quantum field theory. In contrast, [math]dt[/math] is always suitable for any continuum theory, e.g., continuous field of general relativity.

[Guille]

For negative time, [math]t_1>t_2[/math]

Do you believe in negative time?

Or do you mean backwards movement in time?

[AntonioLao]

GUILLE,

The absolute magnitude of time is always a positive number. However, its axis can point in two exactly opposite directions. We can say this only if time is a vector.

[Guille]

GUILLE,

The absolute magnitude of time is always a positive number. However, its axis can point in two exactly opposite directions. We can say this only if time is a vector.

I agree, I mean, some people say that negative time is the time from the big bang backwarsds, but no, that is just an adherence to the time dimensions, it's just going backwards in the dimension of time.

Now, can time be something other than a vector? for example, a tensor, scalar or matrix?

[AntonioLao]

GUILLE,

the important point i tried to keep in mind is whether we can ever change our angle of repose for our unique time axis. This angle determines our destiny, how long we will live?, will we get sick?, etc.

[Guille]

GUILLE,

the important point i tried to keep in mind is whether we can ever change our angle of repose for our unique time axis. This angle determines our destiny, how long we will live?, will we get sick?, etc.

This is quite too much deterministic for me. What determines the time axis we live in?

[AntonioLao]

What determines the time axis we live in?

Believe it or not, it is just Einstein's special theory of relativity. We live in the timelike domain of the lightcone, that is to say all our speeds are less than light speed. However, if our time axis rotates away from the time axis of the universe toward the lightlike surface of the future lightcone then we become light itself and can live almost forever.

[Guille]

Believe it or not, it is just Einstein's special theory of relativity. We live in the timelike domain of the lightcone, that is to say all our speeds are less than light speed. However, if our time axis rotates away from the time axis of the universe toward the lightlike surface of the future lightcone then we become light itself and can live almost forever.

Thanks for the info.

Still, this idea of "lightcones" seems abstract to me.

[AntonioLao]

GUILLE,

The lightcone separates spacetime into three regions: timelike region, lightlike region, and spacelike region. The speed of a particle in the timelike region is less than lightspeed, equal lightspeed in the lightlike region, and superluminal in the spacelike region.

[Guille]

GUILLE,

The lightcone separates spacetime into three regions: timelike region, lightlike region, and spacelike region. The speed of a particle in the timelike region is less than lightspeed, equal lightspeed in the lightlike region, and superluminal in the spacelike region.

What about space-timelike regions? with space-time particles? what speed is it?