Metric expansion of time

[RadicalPi]

It turns out that space is expanding (Expansion of the universe - Wikipedia), and I was wondering if the same were true of time, and if so how.

Many thanks for your answers.

[glowacks]

When you say space is expanding, how exactly are you measuring that if not in reference to time?

[Farmer_Jane]

Go read Stephen Hawking and watch the first four seasons of Lost.

Can’t have space without time.

eta: unless you think of space-time as being without time.

[dzero]

Time is a human construct. To measure time, we use quantum phenomenon which are context dependent. The NIST uses things like a cesium fountain clock to precisely measure time, but it’s precision is dependent on other variables. So time doesn’t exist apart from the observations used to measure it and those are not necessarily fixed.

However as the universe expands to the point where even atoms are torn apart by the expansion, you could say that time will eventually slow to a complete halt since at that point there will be no means by which to measure it.

[panache45]

Time is always expanding. The amount of time since the Big Bang is expanding at the rate of 1 second/second.

[Chronos]

However as the universe expands to the point where even atoms are torn apart by the expansion, you could say that time will eventually slow to a complete halt since at that point there will be no means by which to measure it.

This is probably not true. Current observations are consistent with a “Big Rip” scenario like you describe, but they’re also consistent with the far simpler models where the dark energy remains constant with time (which would not lead to a Rip), and there’s no compelling theoretical reason to suspect we’ll have a Big Rip, either (in fact, theoretical considerations would, if anything, favor the dark energy getting weaker).

And saying that “time is a human construct” is meaningless, since you could say the same thing about absolutely anything else at all.

[Flander]

Soylent green is a human construct.

[Napier]

Mass and energy and information are all made of the same stuff. Quantum mechanical events involve true randomness; they are not deterministic, even if you go all the way down through all the turtles. Thus quantum mechanics generates information, so it’s a source of energy and mass. This is the source of the energy driving the universe apart.

Or not. I don’t know. I just made that up.

[sleestak]

@Flander

Soylent green is a human construct.

And tasty too!

Slee

[dzero]

Rather than start a new thread I figured I post this here.

a new paper suggests that time does not exist as an independent entity. So space-time is not really 3D + time but truly 4D with no time component.

They also suggest an interesting solution to one of Xeno’s paradoxes.

article

They begin by explaining how we usually assume that time is an absolute physical quantity that plays the role of the independent variable (time, t, is often the x-axis on graphs that show the evolution of a physical system). But, as they note, we never really measure t. What we do measure is an object’s frequency, speed, etc. In other words, what experimentally exists are the motion of an object and the tick of a clock, and we compare the object’s motion to the tick of a clock to measure the object’s frequency, speed, etc. By itself, t has only a mathematical value, and no primary physical existence.

This view doesn’t mean that time does not exist, but that time has more to do with space than with the idea of an absolute time. So while 4D spacetime is usually considered to consist of three dimensions of space and one dimension of time, the researchers’ view suggests that it’s more correct to imagine spacetime as four dimensions of space. In other words, as they say, the universe is “timeless.”

“Minkowski space is not 3D + T, it is 4D,” the scientists write in their most recent paper. “The point of view which considers time to be a physical entity in which material changes occur is here replaced with a more convenient view of time being merely the numerical order of material change. This view corresponds better to the physical world and has more explanatory power in describing immediate physical phenomena: gravity, electrostatic interaction, information transfer by EPR experiment are physical phenomena carried directly by the space in which physical phenomena occur.”

As the scientists added, the roots of this idea come from Einstein himself.

“Einstein said, ‘Time has no independent existence apart from the order of events by which we measure it,’” Sorli told PhysOrg.com. “Time is exactly the order of events: this is my conclusion.”

[Asympotically_fat]

dzero, to be honest it looks like rubbish to me

[Half_Man_Half_Wit]

Statements like:

Newton theory on absolute time is not falsifiable, you cannot prove it or disprove it, you have to believe in it

Certainly seem at least a bit odd – under most common readings, ‘absolute time’ is incompatible with relativity, thus falsified by the many tests of it, so either he’s talking about something else (though I don’t see what that could be), or frankly talking rubbish. (Of course, not having read the paper, it might be that the reporting just horribly mangled quotes and context…)

[dzero]

@These are my own pants

dzero, to be honest it looks like rubbish to me

@Half_Man_Half_Wit

Statements like:
Certainly seem at least a bit odd – under most common readings, ‘absolute time’ is incompatible with relativity, thus falsified by the many tests of it, so either he’s talking about something else (though I don’t see what that could be), or frankly talking rubbish. (Of course, not having read the paper, it might be that the reporting just horribly mangled quotes and context…)

Yeah, physorg articles can fall anywhere on the line between stellar and incomprehensible. Being a non-scientist type with just an abiding interest in things like this, i have to say I had a hard time grasping the point. That’s part of the reason I put it here - to see if it added up for anyone else. Guess not.