Physics thermodynamics question on thought experiment.

[geordief]

1 hour ago, swansont said:

But I'm thinking an empty universe with a 1 kg object in it would be basically flat

Is that because of the small ratio of the total mass to the forces holding it together and moving it apart?

 

If it was a larger body then it would be curved?

[swansont]

17 minutes ago, geordief said:

Is that because of the small ratio of the total mass to the forces holding it together and moving it apart?

 

If it was a larger body then it would be curved?

The curvature will depend on its mass. i.e. its gravity. Absent any other influences that might be present, but I was assuming that this was all the universe contained.

1 hour ago, geordief said:

Would the body  have a rotational momentum? Could it not have one?

Whatever momentum it had it would preserve, unless there was some asymmetry in the photon emission.

1 hour ago, geordief said:

As soon as the body starts to radiate  would it also start to re radiate back  inwardly  ?

Why would it? (My question from above). 

[geordief]

7 minutes ago, swansont said:

The curvature will depend on its mass. i.e. its gravity. Absent any other influences that might be present, but I was assuming that this was all the universe contained.

 

Why would it? (My question from above). 

I was also assuming that this mass was all the universe contained....

 

Could not the radiation interact with itself  so that some would be directed back in the direction it originated from- or is a 180 degree turn impossible?

 

Would some of the initial radiation take place at the centre of the body and interact with  the outer part of the body (if,say it was a ball)?

 

Are we allowed to  treat distances as only spatial for such a small mass ?

 

[swansont]

16 minutes ago, geordief said:

 Could not the radiation interact with itself  so that some would be directed back in the direction it originated from- or is a 180 degree turn impossible?

Not sure how that would happen. Momentum is conserved

16 minutes ago, geordief said:

Would some of the initial radiation take place at the centre of the body and interact with  the outer part of the body (if,say it was a ball)?

The thermal radiation we're talking about is emitted from the surface. An asymmetric surface (as mentioned by Sensei) could possibly spin it up and/or give it translational motion, but I don't see how a photon that has gotten far enough away so that it would not be interacting with the body would ever turn around in a flat universe.

 

[J.C.MacSwell]

57 minutes ago, swansont said:

The curvature will depend on its mass. i.e. its gravity. Absent any other influences that might be present, but I was assuming that this was all the universe contained.

 

Would it not depend on it's initial size? If it is small enough it would stay small or even contract?

If it was expanding what would drive the expansion? (or is that unknown but assumed since this one does?)

[Sensei]

47 minutes ago, swansont said:

The thermal radiation we're talking about is emitted from the surface.

...and surface will never be perfect sphere... because of quantization of atoms that make this surface..

It's like pixels on screen. You look at circle on monitor screen, and see no pixels, only after heavy zooming in, they will be revealed.

And usually it'll have anti-aliasing, to hide transition between totally black and totally white pixels.

 

Studiot wanted 1 kg of Iron (Fe-56? Fe-54? There is few stable isotopes).

1000 g / 55.845 g/mol = 17.9067 mol * 6.022141*10^23 = ~1.0784*10^25 atoms.

Arrange them on lattice, one by one..

How much do you need to zoom in to see atoms on spherical curvature..

 

 

Edited October 6, 2017 by Sensei

[swansont]

1 hour ago, J.C.MacSwell said:

Would it not depend on it's initial size? If it is small enough it would stay small or even contract?

If it was expanding what would drive the expansion? (or is that unknown but assumed since this one does?)

What is the "it" here? The object or the universe?

The gravity outside of the object is unaffected by its size. I'm assuming we have some universe in existence and expansion or contraction are moot (though why would it contract? And I have no clue how that would affect photons) 

47 minutes ago, Sensei said:

...and surface will never be perfect sphere... because of quantization of atoms that make this surface..

It's like pixels on screen. You look at circle on monitor screen, and see no pixels, only after heavy zooming in, they will be revealed.

And usually it'll have anti-aliasing, to hide transition between totally black and totally white pixels.

 

Studiot wanted 1 kg of Iron (Fe-56? Fe-54? There is few stable isotopes).

1000 g / 55.845 g/mol = 17.9067 mol * 6.022141*10^23 = ~1.0784*10^25 atoms.

Arrange them on lattice, one by one..

How much do you need to zoom in to see atoms on spherical curvature..

Even if some hit the material, photons will still be emitted, cooling the object down. What's the net effect, other than a slower rate of cooling? The photons will still radiate. The temperature still drops. 

[J.C.MacSwell]

17 minutes ago, swansont said:

What is the "it" here? The object or the universe?

The gravity outside of the object is unaffected by its size. I'm assuming we have some universe in existence and expansion or contraction are moot (though why would it contract? And I have no clue how that would affect photons) 

 

"It" would be the universe. 

I really don't know why a universe would expand, contract, or stay the same but thought mass density might have something to do with it.

[scherado]

On 10/6/2017 at 9:30 AM, swansont said:

But I'm thinking an empty universe with a 1 kg object in it would be basically flat

....and not empty?

[J.C.MacSwell]

10 hours ago, scherado said:

....and not empty?

Starting out just the 1 kg, otherwise empty...I think that was the idea