[MikeS]

Most chemical reactions slow down when cooled.  Cryo-preservation preserves cells as it slows or stops decay by slowing or stopping change.  Another way of accomplishing the same thing (reducing or stopping change), were it possible, would be to dilate local time.

So the question is.
If you cooled the time keeping element (the part that oscillates at a given rate) of an atomic clock to just above absolute zero would local time as measured by the clock dilate and if so by how much?

[CliffordK]

Atomic clocks are based on the hyperfine energy transition of an element, cesium, hydrogen, rubidium, etc, and are somewhat temperature dependent (as you would expect for essentially measuring the energy for the transition).

The cesium and rubidium clocks use an oscillator that creates a microwave that then causes the energy transition at a set frequency.  The energy of the microwave beam is the important part generating the hyperfine transition.  I believe both the cesium and rubidium clocks are round around 100°C.

The hydrogen clocks talk about a hydrogen maser, and apparently is also quite temperature dependent.

This article discusses low temperature Hydrogen clocks and frequency generators.
http://tf.nist.gov/general/pdf/716.pdf

I suppose my question is, if our current timekeeping is measuring energy levels.  And, if one changes energy levels, then is one truly changing time?

[acecharly]

would this not be like measuring a line on a piece of paper, with a metal ruler at room temprature and then measuring the same line with the same ruler cooled to a much lower temprature giving a smaller recorded legnth as the steel had contracted. The line (or time for our example) would be the same but you would perceive a dilation from your initial measurement.

[imatfaal]

Most chemical reactions slow down when cooled.  Cryo-preservation preserves cells as it slows or stops decay by slowing or stopping change.  Another way of accomplishing the same thing (reducing or stopping change), were it possible, would be to dilate local time.

So the question is.
If you cooled the time keeping element (the part that oscillates at a given rate) of an atomic clock to just above absolute zero would local time as measured by the clock dilate and if so by how much?

It's an atomic model not a chemical one - different rules apply.

Rubidium fountain clocks - pretty close to gold standard injects rubidium at ~2x10-6 K; that's just over abszero.  In fact the Systeme Intenationale assumes the atoms in transition to be in a black body state of non-radiation (ie the unreachable zero K) - corrections are made for the fact that they are not. 

Whatever - even if it mattered (and it does not) it would not dilate time, it would affect how we measure it!

[syhprum]

There seem to be basicly two types of clock those with an oscillator controlled by gravitational forces and those with oscillators controlled by inter atomic forces, are there any other possibilities.

[CliffordK]

The atomic clocks have essentially a tunable oscillator used to emit microwaves, that is being calibrated with the hyperfine transition of the target atoms...  cesium, or rubidium.  I think the hydrogen clock is similar, but slightly different.

So it isn't important how the oscillator is affected by the gravitational forces, or velocity, or whatnot, but rather how the hyperfine energy transition state is affected by gravity, velocity, and etc.

Quartz clocks, of course, are dependent on the primary oscillator. 

[MikeS]

The atomic clocks have essentially a tunable oscillator used to emit microwaves, that is being calibrated with the hyperfine transition of the target atoms...  cesium, or rubidium.  I think the hydrogen clock is similar, but slightly different.

So it isn't important how the oscillator is affected by the gravitational forces, or velocity, or whatnot, but rather how the hyperfine energy transition state is affected by gravity, velocity, and etc.

Quartz clocks, of course, are dependent on the primary oscillator. 

Isn't that the same thing?

[imatfaal]

There seem to be basicly two types of clock those with an oscillator controlled by gravitational forces and those with oscillators controlled by inter atomic forces, are there any other possibilities.

My watch works on a torsion basis ie a driven rotational spring oscillation - I think.

http://www.rolex.com/en#/world-of-rolex/about-rolex/parachrom-hairspring

[MikeS]

There seem to be basicly two types of clock those with an oscillator controlled by gravitational forces and those with oscillators controlled by inter atomic forces, are there any other possibilities.

My watch works on a torsion basis ie a driven rotational spring oscillation - I think.

http://www.rolex.com/en#/world-of-rolex/about-rolex/parachrom-hairspring

In what way is that gravity dependant?  It is I believe but I am interested in your answer.

[syhprum]

Mike S
You have in your watch the interplay of the inertia of the mass of the flywheel and the flexing of the hair spring that is mediated by the attractive force between molecules which results from the exchange of virtual Photons.
Inertia is a difficult subject I tend to side with Mach.

[yor_on]

Time has an arrow. In a controlled environment of an even temperature using as identical time measuring devices as possible you will find that gravity delivers different 'rates' to those time devices, relative an 'observer'. That's what NIST do..

Cold can do a lot of things to matter, but it's no time machine, even though it influence the rate of measuring.

[MikeS]

Imagine a hypothetical universe that contains only a black hole.  The temperature is just above absolute zero.  The arrow of time still exists due to the mass of the black hole but time is dilated to the point where time has almost stopped.

Due you agree?

[imatfaal]

Well if hawking was right it wouldn't just contain the blackhole - it would have hawking radiation, creating a background temperature of the universe.

"The arrow of time still exists due to the mass..." - without hawking radiation (and cosmological constant expansion) you would struggle to show anything that wasn't happening as much in one direction as the other.

Time 25 Glyr from the blackhole is fast-ticking compared to that 1 lyr from the blackhole -  you have to specify two points/frames to talking about dilated time.  time isn't just dilated - it is dilated compared to somewhere else, it is relative velocities, differences in grav potential.

but time for what? I am not convinced on the utility of talking about time in a universe with no matter outside a blackhole

[MikeS]

Well if hawking was right it wouldn't just contain the blackhole - it would have hawking radiation, creating a background temperature of the universe.

"The arrow of time still exists due to the mass..." - without hawking radiation (and cosmological constant expansion) you would struggle to show anything that wasn't happening as much in one direction as the other.

Time 25 Glyr from the blackhole is fast-ticking compared to that 1 lyr from the blackhole [/color]-  you have to specify two points/frames to talking about dilated time.  time isn't just dilated - it is dilated compared to somewhere else, it is relative velocities, differences in grav potential.

but time for what? I am not convinced on the utility of talking about time in a universe with no matter outside a blackhole

That's why I said " The temperature is just above absolute zero.".
That's what I was getting at without radiation there would but no passage of time.  The gravity of the black hole shows the arrow of time.  If there were another object in that universe it would be attracted by the black hole.
If this universe only contained a black hole there would be no expansion of space.  It requires at least two objects for expansion of space to be observed and real.
But if the universe contained no (or little) radiation the temperature would be at or close to absolute zero.  Would a clock tick at all anywhere in that universe.  It would tick very, very slowly I suspect.  Were it not for Hawkin radiation it would not tick at all.  Also without the passage of time, distance becomes meaningless.
It's just a thought experiment meant to help clarify the intricacies of time and gravity.

[CliffordK]

I suppose one might ask what the meaning of time is near absolute zero.

• A crystal oscillator (quartz clock) would surly essentially stop at absolute zero.
  
• A pendulum clock might still run, as long as all the bearings were free.
• One might be able to build a nuclear decay clock.  Notes I'm seeing indicate that nuclear decay is relatively temperature independent, so you could count nuclear disintegrations at different temperatures to get a disintegration rate.
• Certainly ageing of biological samples slows down at very low temperatures, and thus sperm can be kept in frozen state for a very long time.
• Notes I'm seeing indicate that atomic clocks (based on hyperfine energies) are in fact temperature dependent as one might expect by changing their energy levels.

So. as atomic motion slows down with cooling, does time also slow down?  It would all depend on one's definition of time.

[syhprum]

If one builds one quartz clock in the same manner as an atomic clock i.e accertain its resonant frequency by external means I see no reason why it should cease to work at near zero °K.
Your nuclear decay clock would not be very accurate as there is some evidence that the rate of decay is influenced by the Nuetrino flux as the Earth moves around the sun in its eliptical orbit.

http://physicsworld.com/cws/article/news/36108

[JP]

If one builds one quartz clock in the same manner as an atomic clock i.e accertain its resonant frequency by external means I see no reason why it should cease to work at near zero °K.

Well, by making it resonate, you've significantly moved it away from absolute zero...

[CliffordK]

Obviously nuclear decay is a random event, so it would be difficult to make a highly precise "clock".  But, it would be easy enough to build a comparative system to look at time.

For example take a homogeneous sample of something with a short half-life like radioactive phosphorous.  Split it in half.  Freeze one sample to below 1K, or a fraction thereof, and keep the other sample at room temperature.

After a few months, warm both samples up to the same temperature and compare the residual activity.

I suppose the point is...  if one considers "time" to be affected by supercooling a substance, then that would mean that all clocks should be affected by the supercooling.

[MikeS]

Would it be fair to sum the subject up as follows?

For a clock to 'tick' it requires energy.  Without energy there can be no passage of time.

That's why the entropy (of a closed system) always increases over time.

[syhprum]

How about your pendulem clock, I see no way that gravity can be affected by temperature.

[yor_on]

Maybe, you can think of it that way?

I'm not sure. It has to do with what you believe 'time' is. Assume you freeze something down, whatever motion there is in that ? will stop, although not for you observing it. Maybe Mike, although you will still have the arrow everywhere else it could be said to 'slow down'. My brain is sloow today :), Friday yesterday. The problem is that you mix temperature with 'time' here which makes me head hurt, well, for now. But it's a good question.

[JP]

Without energy, the entire concept of time has problems, since nothing would change.  If nothing changed, time would be a meaningless concept.

But that's not an issue in reality, since we can never remove all energy from a system.  Even if we're at the zero-point energy (the lowest you can get in any system), there is still energy.

[yor_on]

Yes JP,  I was wondering too, although in terms of 'indeterminacy'. But is that the same as 'energy'? I don't know there?
Indeterminacy isn't a 'motion' in itself but??

[yor_on]

If I use the concept of 'virtual particles' any 'energy' is allowed as long, as it's fast enough whatever that means, under or over Plank time. That statement creates an question of what 'energy' really is thought to be, something 'unlimited' but regulated inside Plank time, or??

Ah well, some day my head will stop aching, hopefully :)

[MikeS]

How about your pendulem clock, I see no way that gravity can be affected by temperature.

Temperature possibly does not affect gravity but gravity does affect temperature.  If you increase the strength of the gravitational field towards infinity as in a black hole then the black hole will absorb everything including radiation (energy) and the temperature will drop approaching absolute zero.