- #1

ryan albery

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**c**oefficient of

**t**hermal

**e**xpansion... analogous to the CTE of water? An inflection with density in regards to temperature?

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- Thread starter ryan albery
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In summary: I see no reason to treat 'space' as possessing any ponderable properties [to borrow from Einstein]. It does appear, however, it can be treated as a field. Does that constitute a 'property'? That is unclear to me.I can understand how 'space' itself doesn't have any ponderable properties, but spacetime, I think even Einstein came to think of 'it' as a thing.If you can't describe how one would go about measuring it, it's not science.

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ryan albery

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Space news on Phys.org

- #2

Naty1

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dark energy, or not, who knows? Energy density, maybe; heat, not so much as far I can see.

If heat is transfrerred via conduction, convection and radiation, you'd need a mechanism that associates those kind of changes with varying cosmological expansion rates. But cosmological expansion doesn't seem well described temperature. Not only is the universe currently the coolest it has ever been, around 2.7 degrees C these days, expansion is currently accelerating as the universe continues to cool. And it expanded superluminally when it was really, really hot and cooling. So what expands superluminally when hot and cold and continues as it approaches absolute zero?

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Mordred

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http://en.wikipedia.org/wiki/Equation_of_state_(cosmology)

http://en.wikipedia.org/wiki/Ideal_gas_law any cosmological model involves temperature due to the above. as well as other interactions, such as GR and chemical interactions.

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ryan albery

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Density and pressure seem not 'in general' linearly/proportional to temperature, like an ideal gas.

- #5

Vanadium 50

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ryan albery said:coefficient ofthermalexpansion... analogous to the CTE of water? An inflection with density in regards to temperature?

No. How would you measure such a thing?

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ryan albery

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Vanadium 50 said:No. How would you measure such a thing?

Same way as you'd measure the expansion/contraction of the universe, only assuming spacetime is an actual thing.

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Chronos

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- #8

ryan albery

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- #9

Naty1

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Maybe our ideas of space and time, or spacetime are so far myopic. Carlo Rovelli describes some discordances:

In SR, if you move along at a constant velocity, your time ticks off at a steady pace. Not so in GR...Proper time along a path [called a worldline] is an observable but it is not 'ticks at a steady pace'...

The proper time, tau, along spacetime trajectories cannot be used as an independent variable either, as tau is a complicated non-local function of the gravitational field itself. Therefore, properly speaking, GR does not admit a description as a system evolving in terms of an observable time variable. ...

This weakening of the notion of time in classical GR is rarely emphasized: After all, in classical

GR we may disregard the full dynamical structure of the theory and consider only individual solutions of its equations of motion. A single solution of the GR equations of motion determines “a spacetime”, where a notion of proper time is associated to each timelike worldline...

But in the quantum context a single solution of the dynamical equation is like a single “trajectory” of a quantum particle: in quantum theory there are no physical individual trajectories: there are only transition probabilities between observable eigenvalues.Therefore in quantum gravity it is likely to be impossible to describe the world in terms of a spacetime,in the same sense in which the motion of a quantum electron cannot be described in terms of a single trajectory.

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ryan albery

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Is there any definition for a temperature of the 'vacuum' of spacetime?

- #11

ryan albery

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What's the Planck Temperature really mean?

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Vanadium 50

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If you can't describe how one would go about measuring it, it's not science.

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ryan albery

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- #14

ryan albery

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- #15

Mordred

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However in all calculations the temperature drops as a result of a change in volume. Regardless of which time period your discussing. The exception to that rule is if new interactions occur from new particles coming into measurable existence. Oft termed az freezing into existence in some high energy particle physics textbooks

- #16

ryan albery

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Does the idea of 'absolute hot' make sense?

- #17

Vanadium 50

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Ryan, you're hijacking your own thread here. And no it doesn't.

A thermal expansion coefficient of spacetime is a measure of how much spacetime expands or contracts in response to changes in temperature. It is similar to the concept of thermal expansion in materials, where an increase in temperature causes the material to expand.

The thermal expansion coefficient of spacetime is measured by observing the changes in the fabric of spacetime in response to changes in temperature. This can be done through experiments and observations of celestial bodies and their movements.

The thermal expansion coefficient of spacetime can be affected by various factors such as the mass and energy density of the universe, the distribution of matter and energy, and the presence of gravitational waves.

A high thermal expansion coefficient of spacetime could indicate that the universe is expanding at an accelerated rate, which could have significant implications for our understanding of the origins and fate of the universe.

Yes, the thermal expansion coefficient of spacetime can change over time as the universe evolves and its properties change. This is why ongoing research and observations are crucial in understanding the nature of spacetime and its expansion.

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