Silly thought experiment on the equivalence of mass and energy.

[mzatanoskas]

Hello everyone.

 

I sometimes get niggling questions, or half baked ideas about science/religion/philosophy or whatever that keep me up tossing and turning for oh... a good 5 minutes at night. The other day I decided I might as well register on some forums where clever people could tell me what was what, and I might actually benefit from my midnight pondering.

 

So here goes my confused thought experiment #1:

 

I started thinking about this after reading some article talking about the geology of the earth, please excuse any shocking beginner logical/scientific mistakes!

 

 

1. Imagine a large mass of rock in space, say the size of our moon.

 

2. The gravity of the moon causes pressure on the rock inside the moon, and this pressure causes the rock to heat up.

 

3. This heat conducts/convects to the surface and then radiates out into space.

 

4. Now jump forward some ridiculous amount of time. If the moon has the same mass, then presumably it is still emitting heat and we have just flouted the first law of thermodynamics.

 

5. The implication therefore is that as the moon radiates heat, so it is losing mass. Over time, the mass would be less, gravity less and heat emitted less. Hence mass and energy are the same thing or intimately related.

 

 

Well that was my thought process. So my questions are:

 

1. Is that essentially a coherent thought experiment, or am I making any terrible mistakes?

 

2. If valid, then what is the actual mechanism at a molecular level of this kind of heat decay?

 

3. That will do for now.

 

Thanks for putting me right guys!

[John Cuthber]

The heat radiated off into space was originally stored in the "moon" when you made it.

Imagine I have a moon with a big rock on a table. A passing meteor knocks the rock off the table. The energy released is lost as heat by radiation (over time).

No violation of anything- it just lost the energy I put in to lifting the rock onto the table in the first place.

Imagine doing this with so many rocks that they wedged one-another up and didn't need the table.

[mzatanoskas]

Thanks for your reply John. After reading your post a couple of times and that gravitational potential >> kinetic >> heat stuff, I think I realise where I was going wrong.

 

I seemed to be imagining pressure itself as creating heat, instead of an increase in pressure creating heat.

 

So all that is really happening in my example is that when the moon is initially formed, gravity compacts the rocks and pressure increases and the temperature goes up. Like when you pump up a bicycle tyre.

 

Once you stop increasing that pressure, then no more heat is generated. The tyre and the moon just cool down.

 

So over time, all you get is a cold moon. No new radical theory of thermodynamic mass/energy equivalential heat decay.

 

 

Thanks again John, I learned something today.

 

My reconstructed thought experiment:

 

 

1. Imagine a large mass of rock in space, say the size of our moon.

 

2. When the moon is created, the gravity of the moon causes pressure on the rock inside the moon, and this increase in pressure causes the rock to heat up.

 

3. This heat conducts/convects to the surface and then radiates out into space.

 

4. Now jump forward some ridiculous amount of time. The moon is now cold.

 

5. The implication therefore is that nothing of any great interest has happened here at all.

 

 

1 confused thought down, many, many more to go...

Edited October 21, 2009 by mzatanoskas

[swansont]

I seemed to be imagining pressure itself as creating heat, instead of an increase in pressure creating heat.

 

A system under pressure has some energy, but you supplied that energy in creating that pressure. If you increase the pressure, work is being done somewhere, or some other conversion is taking place. Energy can be stored in a number of forms, and you have to account for all of them.

[kanyalsingh]

you supplied that energy in creating that pressure. If you increase the pressure, work is being done somewhere, or some other conversion is taking place. Energy can be stored in a number of forms, and you have to account for all of them.

Edited November 4, 2009 by swansont
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