TIME

[socratus]

Time.
The past is fixed and clear.
It is impossible to revive the time that has gone into the past.
The future is subject to the Heisenberg uncertainty principle: ΔE Δt ≈ ħ/4π.
"Time" is created by gravity matter and energy (quantum energy).
"Time" is a relative concept.
Without gravity and quantum energy the universe has no time.
It is eternal (and infinite).
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[Dratonia]

Yeah, I'm not even going to try and comprehend time from a scientific perspective.

 

[billslugg]

From a scientific perspective, the dimension of time is required to differentiate between two events, one of which caused the other. Roger Penrose writes that once there are no more particles in the universe, time will no longer exist.

 

[SyfoDias]

It's a real head messer. Where does the time go? Nowhere I suppose, if it didnt exist

 

[ASTROSTONER]

Are/were there any experimental proofs that show the speed of time as constant? Any proof that a second today was the same relative length as a second in the distance past?

 

[billslugg]

The speed of time is not constant but varies all over the universe. Any two objects moving relative to each other have different clocks. The other guy's clock is going slower. The speed of time also varies according to how strong the local gravitational field is and it varies by how strong the local electric field is.
In the very early universe, where mass density was much greater, time would have run slower.

 

[spacedweller]

"Time" is created by gravity matter and energy (quantum energy).

Roger Penrose writes that once there are no more particles in the universe, time will no longer exist.

This is very interesting, because in philosophical world there is spear breaking around "what is time?", I recommend anyone interested to study McTaggart's definition of time, ex:

https://en.wikipedia.org/wiki/The_Unreality_of_Time

In any case I find it difficult to imagine anything without time, a static 3D space with no change, no time feels like very unrealistic.

 

[ASTROSTONER]

In the very early universe, where mass density was much greater, time would have run slower.

i imagine if graphed it would follow an exponential curve with the asymptote approaching our current speed of time. still ever changing so slightly. Has anyone ever measure this change?

 

[billslugg]

i imagine if graphed it would follow an exponential curve with the asymptote approaching our current speed of time. still ever changing so slightly. Has anyone ever measure this change?

There would be no way to go into the past and measure time there but there have been experiments with atomic clocks that show the dilation due to how strong the gravitational field is.

 

[ASTROSTONER]

There would be no way to go into the past and measure time there but there have been experiments with atomic clocks that show the dilation due to how strong the gravitational field is.

ok even if time travel is impossible, still we look at the distant stars and we see the past. No way to measure the change with this window into the past?

 

[billslugg]

We can look into the past and we can travel to the future but we cannot travel to the past nor look into the future.
We can look at the spectrum of light emitted billions of years ago and we see the same features as today. If the rate time passes were different those features would not be the same.

 

[ASTROSTONER]

We can look at the spectrum of light emitted billions of years ago and we see the same features as today. If the rate time passes were different those features would not be the same.

Do those features look the same?

I guess if time is faster now then in the past then the further you look, the slower the frequencies would get.
Do you think light would become redshifted if you looked far enough back?

 

[billslugg]

The frequencies become lower due to the very fast rate the distant galaxies are receding.
We know by a large number of overlapping yardsticks just how far away distant galaxies are. We know that the farther away they are the more they are redshifted. The amount of time since the universe was created and the distance away they are tells us how fast they must be travelling. This speed accounts for the red shift. There is no need to think the rate at which time passes has changed. Note, however, there is no constancy to time anywhere at any time. Time goes faster or slower depending on velocity, gravitational field strength and charge.
Also note that time means nothing to a photon. Photon is going at light speed. At light speed the clock is stopped.

 

[ASTROSTONER]

"There is no need to think the rate at which time passes has changed. "

"In the very early universe, where mass density was much greater, time would have run slower. "

do you see the contradiction?

 

[billslugg]

Yes, it is hard to understand that something that is different to every observer has not changed. We can only say that each observer, in their rest frame, sees a clock that runs at exactly the same speed as every other observer sees in their rest frame and that rate has never changed. Unfortunately there is no way to compare them since every frame is at a different location, going a different speed, at a different time, under a different amount of gravity and charge. All of those effects can be adjusted for however and we can calculate that time passes at the same rate in their frame but I suppose we can never be sure since we cannot actually be there.

 

[Unclear Engineer]

I think Astrostoner's point is that we are assuming that redshift is caused by the expansion of space, but not considering if it could instead be caused by decreases in the rate of time passage with distance. That might be reasonably considered if we are seeing older things that are farther away doing things slower in the past. with the more distant past being the more physically distant objects. So, it would not be space expanding everywhere, instead, it would be time speeding up everywhere.

Considering that we talk about "space/time' as a 4-dimensional space, it has always seemed odd to me that we postulate space as expanding, but time dimension remaining static while space expands.

Why does the time dimension need to remain static?

 

[karlp295]

Time is something we cannot understand at the present time. We can speculate, but we don't know if we can travel backwards. Until we do know one way or the other for sure we should all remain open-minded.

Since a kid I have always thought that maybe ALL times can coexist simultaneously but again there is no proof for this theory....yet

 

[Curiosity killed the cat]

Most of us have an opinion of what spacetime is, and a brief summation of my own opinion would be this...

Time is not a standalone phenomenon, Einstein and Minkowski made that abundantly clear to us all. they both stated that spacetime, is a single phenomenon, which should not be mistakenly perceived as two separate phenomena. Unfortunately Minkowski appeared to have contradicted himself, with his postulate of three dimensions of space, and one of time, representing spacetime.

Minkowski spacetime is actually a mathematical coordinate system, which can be used to determine the location of other objects within this instance of space-time, relative to the observer. I don't think Minkowski ever intended anyone to accept it as an explanation of the fundamental nature of spacetime.

I concur with Einsteins' postulate that space-time constitutes a geometry within which spacetime can be curved by the proximity of matter/mass with gravitation being the effect of that curvature. John Archibald Wheeler got it right when he said that... Spacetime tells matter how to move; matter tells spacetime how to curve.

The metric/scale of spacetime is not fixed. Space-time can be expanded or compressed, but the ratio of spacetime (aka the speed of causality) is fixed. this is why the speed of light appears the same to all observers, and the ratio also prevents an effect from preceding its cause. Or, as Minkowski put it, "preserves an independent reality."