14 Jan 05
I remember this. Wasn't it on some kid's final exam or something? It was a pretty funny answer to read.
I'd say it's neither. It releases no heat and absorbs no heat, as it's not physically attainable from this universe - only your soul goes there. As it has no physical connection with this universe, heat cannot pass either way.
14 Jan 05
I wonder, where does all the heat in the universe go? Heat is energy transfer as a result of a temperature difference, so all the objects in the universe above absolute zero are radiating heat to whatever cooler objects/spaces are around. But where does heat at the "edge" of the universe go (if such an boundary can and does actually exist)? Does it just head out and never return? If it does, where is it going? What's the object/space that's attracting/receiving the energy? If there is something there, doesn't that mean the "edge" of the universe isn't really the edge? If the heat doesn't go beyond some sort of boundary, why not?
That will mess with your head.
15 Jan 05
Originally posted by PBE6Is there a theoretical answer to this? I mean, if I put an oven in a
I wonder, where does all the heat in the universe go? Heat is energy transfer as a result of a temperature difference, so all the objects in the universe above absolute zero are radiating heat to whatever cooler objects/spaces are around. But where does heat at the "edge" of the universe go (if such an boundary can and does actually exist)? Does it just he ...[text shortened]... If the heat doesn't go beyond some sort of boundary, why not?
That will mess with your head.
perfect vacuum, are you saying that it doesn't radiate any heat because
there is nothing to attract the energy?
Nemesio
16 Jan 05
Originally posted by PBE6In the 'Big Bang' model, everything (matter and energy) is spreading out in all directions, so the 'edge', such as one exists, is moving away from us at the speed of light.
I wonder, where does all the heat in the universe go? Heat is energy transfer as a result of a temperature difference, so all the objects in the universe above absolute zero are radiating heat to whatever cooler objects/spaces are around. But where does heat at the "edge" of the universe go (if such an boundary can and does actually exist)? Does it just he ...[text shortened]... If the heat doesn't go beyond some sort of boundary, why not?
That will mess with your head.
17 Jan 05
Originally posted by AcolyteDoesn't current thinking suggest that space is curved? Thus if anything ever reaches the edge of the universe, it will actually be back where it started.
In the 'Big Bang' model, everything (matter and energy) is spreading out in all directions, so the 'edge', such as one exists, is moving away from us at the speed of light.
17 Jan 05
Originally posted by NemesioI assume by "perfect vacuum" you mean putting an oven in a universe with nothing else in it. I have no idea what would happen in that case. I guess energy would be radiating from the oven, but where would it go? And would it be due to a temperature difference between the oven and the surroundings (if not, it's not heat)?
Is there a theoretical answer to this? I mean, if I put an oven in a
perfect vacuum, are you saying that it doesn't radiate any heat because
there is nothing to attract the energy?
Nemesio
What would the temperature of the surroundings be, anyway? That's not as dumb a question as it sounds - temperature is a measure of the average kinetic energy of the atoms, molecules and other components that make up some object. If there's no stuff, what do we mean by "temperature"?
Things that make you go...hmm...
17 Jan 05
Originally posted by PBE6Temperature doesn't really measure this - for example, a puddle of water at room temperature has much more internal kinetic energy than a lump of copper of the same mass and temperature. Temperature measures the propensity of something to transfer its internal kinetic energy to its surroundings. So once the space around the oven has photons in it (from the oven), its temperature is above absolute zero.
What would the temperature of the surroundings be, anyway? That's not as dumb a question as it sounds - temperature is a measure of the average kinetic energy of the atoms, molecules and other components that make up some object. If there's no stuff, what do we mean by "temperature"?
17 Jan 05
Originally posted by AcolyteWe should clarify. There are many definitions of temperature, one of them being "the average kinetic energy of the components of an object", another being "the propensity of an object to give up kinetic energy to another object". There are others, too. No definition is useful or applicable in all cases.
Temperature doesn't really measure this - for example, a puddle of water at room temperature has much more internal kinetic energy than a lump of copper of the same mass and temperature. Temperature measures the propensity of something to transfer its internal kinetic energy to its surroundings. So once the space around the oven has photons in it (from the oven), its temperature is above absolute zero.
When we measure temperature with a standard thermometer, we actually are measuring the average kinetic energy of the part of the object that the thermometer is in conact with. Of course, this type of measurement is not particularly useful if we have less than about 10^6 particles to measure (an extremely small number of particles compared), about what is required for a good statistical average. And the lump of copper and the puddle do have the same average kinetic energy, provided they are both at the same temperature (room temperature).
The zeroth law definition describes two bodies being of equal temperature if they are in thermal contact and they are in thermal equilibrium (no energy transfer). This definition works too, but it's hard to test a small collection of atoms by getting another small collection of atoms and seeing if there is any energy transfer.
There's also a definition that refers to the change in entropy with the addition of energy to a system. This one allows us to define negative temperatures which are neat, but measuring the entropy of a real system is not always easy.
Having said all that, Acolyte is exactly right when he says that as the object radiates heat in the form of electromagnetic waves, the vacuum is no longer a vacuum. Outer space is generally reported as having a background temperature of about 3 K for this reason.
So I guess the oven would heat up space until it was in thermal equilibrium with it, making the oven pretty f'n cold eventually.
Now I guess the heat will continue to travel off into space until it hits something, or hits the edge of the universe. According to Acolyte, energy will never catch the edge of the universe because it's moving at the speed of light. My question is, what's on the other side of the edge? What does it mean to be on the other side of existence? How do we define the edge of existence?
🙄
Crazy.
19 Jan 05
Originally posted by AThousandYoungThe usual way of explaining it is to imagine a being that lives in two dimensions, on a perfectly smooth planet. From his perspective, the planet is flat, because he has no conception of a third dimension for it to be round in. So, if he travels all he way around his world, he's going to be confused to find himself back where he started.
Is that what they mean when they say space is curved? I never understood that statement.
Now add a dimension. We are now in the position of the 2d creature. Space is curved in a fourth dimension of which we have no comprehension.
It took me a while to get my head around it, even with this explanation
26 Jan 05
Now add a dimension. We are now in the position of the 2d creature. Space is curved in a fourth dimension of which we have no comprehension.Is that how it works? I had heard the universe was infinite in area but bounded, like a sphere. Since its surface bears an infinite number of points, ergo infinite area, but points beyond that surface can also be defined, the area is infinite but bounded. That still doesn't answer the question of what exists beyond the edge of the universe, though. It has to have some tangible reality, if it can be understood in terms of not-universe.
27 Jan 05
1 edit
Originally posted by greendragonIf it has infinite volume, it can't be bounded, and spheres are always finite. But there is a space which you might see as having infinite area, which is in some sense sphere-like:
Is that how it works? I had heard the universe was infinite in area but bounded, like a sphere. Since its surface bears an infinite number of points, ergo infinite area, but points beyond that surface can also be defined, the area is in ...[text shortened]... ngible reality, if it can be understood in terms of not-universe.
Start with an ordinary plane, stretching off to infinity. If we ignore the limits imposed by the speed of light etc, you can see infinitely far in all directions. Now suppose that, instead of a horizon, there is a single 'point at infinity', so that if you were to draw a straight line in any direction away from yourself, it would lead to the point at infinity. It's not hard to show that the plane together with this extra point is topologically the same as a sphere. Also, there's no need to think about 'edges', as this space doesn't have any (even the point at infinity is surrounded by the rest of the plane, so that doesn't cause problems). The trouble with this representation is that the point at infinity is infinitely far away from everything else, so you don't get a proper formulation of 'length' and 'area' over the space as a whole.