Universal 'Now' at Time-Zero

[Strange]

A related question, how fast would time be moving at T = 30 sec as compared to today's Universal time?

 

The only way of comparing them would be by using "proper time" - the time as measured by a clock at that point. In which case, answer is 1s per second.

[Mordred]

When the universe was in the hot, dense state, was everything causally connected and the time, if it existed at that point, was the same everywhere until inhomogeneity occured i.e. space formed and photons/information could travel?

 

Edit: Might be in the the wrong forum; I just realised Relativity goes awry at time-zero.

Lets look back at this OP. We need to clear up a few misconceptions on time.

 

Inhomogeneous mass distribution is needed for time dilation. However time still functions.

 

So if you take a homogeneous and isotropic fluid two static observers in that fluid regardless of location will measure no time dilation regardless of location. Time still functions.

 

Many ppl tend to believe that a higher density past compared to density now but this isn't true. The hyperslice of an event is homogeneous and isotropic.

 

Now in an expanding volume how causal connection is defined gets a little more complex than simply considering just the speed of light and time it takes for information exchange.

 

We must also account for the expansion.

 

Now the distinction above may be better explained by the following.

 

example A. Use the Schwartzchild metric ie a Bh or planet. The Global geometry is a homogeneous and isotropic fluid. It will have an "as close to universal density as possible". |||The Schwartzchild metric assumes zero value for the vacuum|||. However this isn't true in other metrics.

 

So in this case your global hyperslice is uniform. Homogenous and isotropic. Any two or more static observers, observing each other will have the same time rate.

 

A global observer can set this as a universal "now".

 

the global geometry will be

[latex]ct,x,y,z [/latex] which is Euclidean flat. The observer at the EH will also use the same geometry for his reference frame.

 

When you draw a line between the Global to local observer the lightpath is curved by the localized anistrophy. However in this case the volume isn't changing...

 

In the case of the FLRW metric the observers global event is still a homogenous and isotropic fluid but the change in density is due to a change in volume. Not the gravitational potential.

 

in other words what is curved from one observer to the other is density change due to change in volume. Where as in the first case the volume is constant.

 

This is an important distinction between the Einstein field equations and the FLRW metric.

Edited August 17, 2016 by Mordred

[MigL]

As mentioned before.

As you run time backwards, the universe shrinks.

 

If it stops shrinking at a size where quantum effects are negligible, then you have geometry ( space-time ), so you can talk about 'now' or 'before' meaningfully.

 

If it shrinks past that point, nobody knows, as we don't have a quantum gravity theory to describe that kind of space-time.

It could be a totally different kind of geometry ( or none at all ), like J.A. Wheeler's quantum foam, or quantized, discrete space-time of LQG, or 11 dimensional branes in the bulk of SS theory. And so, no-one knows what this implies for a discussion of time and sequence.

 

If it shrinks down to singular size then there cannot be geometry and therefore, no space-time.

In effect, you are then 'north of the north pole'.

[michel123456]

As mentioned before.

As you run time backwards, the universe shrinks.

 

If it stops shrinking at a size where quantum effects are negligible, then you have geometry ( space-time ), so you can talk about 'now' or 'before' meaningfully.

 

If it shrinks past that point, nobody knows, as we don't have a quantum gravity theory to describe that kind of space-time.

It could be a totally different kind of geometry ( or none at all ), like J.A. Wheeler's quantum foam, or quantized, discrete space-time of LQG, or 11 dimensional branes in the bulk of SS theory. And so, no-one knows what this implies for a discussion of time and sequence.

 

If it shrinks down to singular size then there cannot be geometry and therefore, no space-time.

In effect, you are then 'north of the north pole'.

I think that Mordred took it better.

The shrinking is about the metric. The distances as measured by observers in the beginning of the universe has not changed, if I understand clearly what a metric expansion means. Apparent density has not changed. Or has it?

Lets look back at this OP. We need to clear up a few misconceptions on time.

 

Inhomogeneous mass distribution is needed for time dilation. However time still functions.

 

So if you take a homogeneous and isotropic fluid two static observers in that fluid regardless of location will measure no time dilation regardless of location. Time still functions.

 

Many ppl tend to believe that a higher density past compared to density now but this isn't true. The hyperslice of an event is homogeneous and isotropic.

 

Now in an expanding volume how causal connection is defined gets a little more complex than simply considering just the speed of light and time it takes for information exchange.

 

We must also account for the expansion.

 

 

Please expand on this. Eventually correcting me.

Edited August 18, 2016 by michel123456

[MigL]

You need to have geometry to have a metric.

If you're considering a singularity, you have no geometry.

So what exactly is the metric measuring Michel ?

[Bird11dog]

 

The only way of comparing them would be by using "proper time" - the time as measured by a clock at that point. In which case, answer is 1s per second.

With all the mass of the Universe concentrated in a much smaller volume of space why wouldn't time be running much slower than today's time?

[StringJunky]

With all the mass of the Universe concentrated in a much smaller volume of space why wouldn't time be running much slower than today's time?

Relative to what? Itself? Doesn't work does it?

[Bird11dog]

As mentioned before.

As you run time backwards, the universe shrinks.

 

If it stops shrinking at a size where quantum effects are negligible, then you have geometry ( space-time ), so you can talk about 'now' or 'before' meaningfully.

 

If it shrinks past that point, nobody knows, as we don't have a quantum gravity theory to describe that kind of space-time.

It could be a totally different kind of geometry ( or none at all ), like J.A. Wheeler's quantum foam, or quantized, discrete space-time of LQG, or 11 dimensional branes in the bulk of SS theory. And so, no-one knows what this implies for a discussion of time and sequence.

 

If it shrinks down to singular size then there cannot be geometry and therefore, no space-time.

In effect, you are then 'north of the north pole'.

i DON'T THINK YOU HAVE A CLUE AS TO WHAT i AM TALKING ABOUT. THE GRAVITATIONAL FIELD FOR THE UNIVERSE WOULD HAVE BEEN VERY VERY LARGE AS COMPARED TO TODAY, THEREFORE TIME WOULD HAVE BEEN RUNNING MUCH SLOWER THAN TODAY. THIS WOULD MEAN THAT THE SPEED OF LIGHT WAS MUCH GREATER THAN TODAY(MAYBE BY A FACTOR OF AS MUCH AS 100 OR EVAN A 1000) WHICH MAY EXPLAIN THE INFLATION THEORY.

[Strange]

With all the mass of the Universe concentrated in a much smaller volume of space why wouldn't time be running much slower than today's time?

 

How could you tell?

 

i DON'T THINK YOU HAVE A CLUE AS TO WHAT i AM TALKING ABOUT. THE GRAVITATIONAL FIELD FOR THE UNIVERSE WOULD HAVE BEEN VERY VERY LARGE AS COMPARED TO TODAY, THEREFORE TIME WOULD HAVE BEEN RUNNING MUCH SLOWER THAN TODAY. THIS WOULD MEAN THAT THE SPEED OF LIGHT WAS MUCH GREATER THAN TODAY(MAYBE BY A FACTOR OF AS MUCH AS 100 OR EVAN A 1000) WHICH MAY EXPLAIN THE INFLATION THEORY.

 

There is still no way to compare a clock today with a clock then. Therefore the question has no meaning (as all we can talk about is RELATIVE time differences).

 

WHICH MAY EXPLAIN THE INFLATION THEORY.

 

Gosh. I wonder why none of the experts in GR and cosmology have never considered that...

Edited August 18, 2016 by Strange

[michel123456]

You need to have geometry to have a metric.

If you're considering a singularity, you have no geometry.

So what exactly is the metric measuring Michel ?

What I cannot understand is at what time the shrinking of the metric changes and becomes a shrinking of the distance.

in all the BB representations I have read till now it is as if the universe was smaller in the beginning (denser), which means that the distances between the objects was smaller. OTOH it is also said that what is expanding is the metric. So, at some epoch, the change in metric must have changed into a change in distance, or reversely. I guess.

[Strange]

I think they are just different words for the same thing. "The metric" is, as far as I understand, just how distances are defined.

[Mordred]

With all the mass of the Universe concentrated in a much smaller volume of space why wouldn't time be running much slower than today's time?

No the global density is still uniform.

 

I recognize this is tricky. Its common to think higher density means slower time. In the Schwartzchild example this is true.

 

However this isn't true when its the Global geometry changing density through volume change.

 

(we currently have one poster in Speculations trying to prove the above is wrong. Though he realized his math is wrong so is now rethinking)

 

For example Ask yourself Why we do not measure time dilation of standard candles the further away they are from Earth.

 

They are emitting from a higher global density past. So each standard candle or any other interactive process should be more and more time dilated the further you look.

 

Yet we don't see that

 

Cosmological redshift is due to volume change not time dilation.

Edited August 18, 2016 by Mordred

[MigL]

What change are you talking about Michel ?

 

A metric is simply the distance between two points.

In 4d flat ( Minkowsky ) space-time it is simply the extension of Pythagoras to 3 spatial dimensions plus time, given by dS^2.

In curved, GR, the multipliers of the Pythagoras terms are not unitary anymore because of curvature.

 

But in either case you need geometry to have separation, S.

[Mordred]

What change are you talking about Michel ?

 

A metric is simply the distance between two points.

In 4d flat ( Minkowsky ) space-time it is simply the extension of Pythagoras to 3 spatial dimensions plus time, given by dS^2.

In curved, GR, the multipliers of the Pythagoras terms are not unitary anymore because of curvature.

 

But in either case you need geometry to have separation, S.

To add to this. The deviations to Pythagoras theory for Shwartzchild metric (the curvature) is due to strictly stress-energy-momentum/tensor gradient. Which causes time dilation.

 

In the FLRW metric the curvature gradient is a history of expansion and contraction change. The volume is changing by the scale factor a(t). not time dilation. Your deviations from Pythagoras theory is due to this history curvature.

 

In a homogeneous and isotropic universe the global geometry at any time slice is uniform in mass/energy distribution. There is no inherent vector quantity due to gravity. Gravity in this particular case a scalar value. GR deals with the conservation of the four momentum/four velocity. This is expressed by the stress/momentum tensor. In this static case the stress tensor value is zero. There is no deviation in the four momentum/four velocity. Parallel transport of two light rays will always remain parallel with no deviation. So a static uniform mass distribution there is no length contraction nor time dilation. As it is static we also have no expansion/contraction volume change.

 

When you have a localized difference in mass distribution, from the uniform global distribution this changes. Now we have a definable direction to the four momentum etc. The stress tensor is no longer zero, this causes changes to the Reimann curvature. This is where you see time dilation.

 

In the FLRW metric case, The global density lowers, however this change is global as time progresses. At any particular time slice gravity is static. There is no vector component to the average particle momentum. NO change to the stress/momentum tensor. Which means no Reimann curvature. No time dilation.

 

The volume change does not influence the conservation of four momentum except via temperature change (kinetic energy). The changes to separation distance are due to expansion and contraction. Not the energy/momentum tensor. Particles of the present don't interact with particles in the past. The change in density from one moment in time cannot influence a past density.

Edited August 18, 2016 by Mordred

[michel123456]

What change are you talking about Michel ?

 

A metric is simply the distance between two points.

In 4d flat ( Minkowsky ) space-time it is simply the extension of Pythagoras to 3 spatial dimensions plus time, given by dS^2.

In curved, GR, the multipliers of the Pythagoras terms are not unitary anymore because of curvature.

 

But in either case you need geometry to have separation, S.

That is not my understanding. I thought it was about a scale factor. IOW that the value of what we call 1 meter has changed.

[Strange]

That is not my understanding. I thought it was about a scale factor. IOW that the value of what we call 1 meter has changed.

 

 

And that is the same as saying that distance or the metric has changed.

[michel123456]

 

 

And that is the same as saying that distance or the metric has changed.

But these are totally different concepts.

In the expanding space paradigm, the grid is increasing. It represents a scale factor. It is an increase of the metric. The distance remains the same: for example, if A and B are separated 3 grids square before, they still are separated 3 grid squares after.

[MigL]

No.

If the 'units' of your co-ordinate system just expanded, you'd never be able to tell expansion is going on.

The number of units between events actually increases. And it can then be counteracted by local gravity.

[tar]

Thread,

 

So, question.

 

Does the unit measurement between quarks change at the same time as the measurement between galaxies?

 

Regards, TAR

[StringJunky]

Thread,

 

So, question.

 

Does the unit measurement between quarks change at the same time as the measurement between galaxies?

 

Regards, TAR

No, Any things closer than 200 million lightyears apart are bound by forces stronger than expansion.

Edited August 19, 2016 by StringJunky

[tar]

String Junky,

 

So units of measure found on the atomic level or human body level, or planetary level, or solar system level, or galactic level can be used as standard units, that would not change over billions of years of universal expansion?

 

Regards, TAR

[StringJunky]

String Junky,

 

So units of measure found on the atomic level or human body level, or planetary level, or solar system level, or galactic level can be used as standard units, that would not change over billions of years of universal expansion?

 

Regards, TAR

Up to the intergalactic level - within 200MLYS - they won't change, due to the expansion, because the forces binding those, including gravity up to about that range, are too strong.

Edited August 19, 2016 by StringJunky

[tar]

String Junky,

 

I understand the words you are saying, but do not know what they mean in terms of this discussion of what was within causal distances, when the universe was smaller.

 

Plus I am not sure what it is that is expanding, if nothing within 200million lys of anything else is subject to the expansion.

 

Regards, TAR

[StringJunky]

Plus I am not sure what it is that is expanding, if nothing within 200million lys of anything else is subject to the expansion.

Space, distance or volume.

[tar]

String Junky,

 

Probably a question for another thread, but if the distance between A and B does not change because they are within 200million lys of each other and the distance between B and C does not change because they are within 200 million lys of each other, where has the distance between A and C increased, even though they are 400 million lyrs distant and the forces of expansion should be in force?

 

Regards, TAR

Edited August 20, 2016 by tar