I read recently that through the Casimir interaction, heat can be dissipated in a 'vacuum' as it is transferred to virtual particles. When this happens and the virtual particles pop back out of existence, do they carry the energy they absorbed along with them into nonexistence? Or by absorbing energy do they become real? Would that then mean energy is being created?
Cuation-I’m surely an idiot on cosmology and physics.
Current theory is that all mass energy will eventually wind up in black holes - which will then evaporate. All mass energy will then be maximally dispersed in the entropy death of the universe. I think that means the Casimir effect is not destroying mass energy, just dispersing it to a useless state.
And perhaps corporate_shi11 is using "dissipated in a vacuum" to mean "transfer of internal energy from a hotter body to a colder one across a vacuum"?
Heat can be dissipated in a vacuum by electromagnetic radiation. This is how most heat is dissipated in a vacuum.
For the Casimir interaction, virtual particles are one way to do the bookkeeping to calculate the force between two objects. One object transfers energy and momentum to virtual particles which in turn transfer the energy and momentum to another object.
Putting aside the quantum aspects of this article for a moment, (not that they aren't fascinating, but, ...well, one can only think so hard at the end of the day!)
I think this is a good place to link to Sean Carroll's post about the gravitational aspects of the general issue (for anyone who might not have seen it):
https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
Energy is a slippery concept. To Wikipedia it's a 'quantitive property' that 'must be transferred to an object.' A property. Good luck weighing that, or nailing it to a tree.
Consider the 'transformation of energy' ... from mechanical to electrical to acoustical to chemical to potential to kinetic to thermal (end of the line). What is the 'it' that's being transformed?
In one sense all things are 'energetic' so long as they have a velocity (relative to something else). We need to keep an eye on boulders up on hillsides. They're not moving right now ... but their potential energy might be transferred to us, thanks to the equally mysterious 'gravity'.
Yes, the math all seems to work. But we're not quite 'there' yet. Our position is uncertain.
That's an interesting question. AFAIU, heat engines don't take energy from heat, but from heat difference. In this sense, heat is like potential energy - an absolute value is arbitrary and meaningless in isolation, but moving mass between two points of different potential lets you store or extract energy.
OTOH, from what little I remember from reaction kinetics in chemistry, temperature there is used as absolute value that determines the chance of collision between their molecules and the "activation energy", both of which influence the rate of a chemical reaction. In this space, thermal energy seems like something absolute.
> In this sense, heat is like potential energy - an absolute value is arbitrary and meaningless in isolation
Not quite. Potential is defined with an arbitrary basis as you’ve pointed out, but with temperature the basis is not arbitrary: it’s chosen for us, and this value is absolute zero. Taking a temperature difference is not enough to figure out how well a heat engine will work on it.
Note that general relativity requires you to precisely locate all (non-gravitational) energy contributions as they determine spacetime curvature. So while eg the electrostatic potential has an arbitrary zero point, the energy density of the electromagnetic field has not.
The only exception to that is gravitational energy, which cannot entirely be localized.
Energy is the ability to perform work. It doesn't have to be a velocity. A boulder on the hillside is energetic because it can fall down, thereby performing work on whatever it falls on.
Many of the primitive notions that emerge in scientific theories don't correspond to a category like "object I can hold in my hand". Energy is one. Momentum is another. Gene and species in biology. Electronegativity in chemistry. Power dynamic in history. Schema in child psychology.
> What is the 'it' that's being transformed?
This is exactly what led to the caloric theory of heat. But nonphysical transfer isn't terribly slippery. Take a rumor. I whisper to someone, who whispers to someone...there is no physical transfer here, merely a transfer of configuration. Transfer of energy, like transfer of genes, is more like that. Nor need it correspond to any particular physical part of a thing, e.g., where is the sarcasm in a sentence?
Locally conserved invariants like energy or momentum don't correspond to any of the categories that we learn in childhood, but that doesn't make them particularly slippery, just unfamiliar.
At least this one has a direct title. The other "but what if we ignore thermodynamics for a moment" articles that pass by HN sometimes bury the lede a bit.
Considered abandoning reading when I saw the ridiculous "if we believe in dark matter, why not aliens?" headline on the side. Did stop reading when they started talking about quantum mechanical observations. Is Nautilus just a Markov generator trained on terrible Quora answers?
This is not really fair. The "why not aliens" article is an interview with a scientist who argues that we should not outright dismiss the possibility that something (particularly omuamua comet) is alien technology, until we have proof one way or the other, which is not a ridiculous thing to say.
I also can't see what is particularly wrong with the description of quantum mechanical observations in this article. It looks to me like a good enough description of the idea of research done by the author himself.
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[ 3.1 ms ] story [ 56.9 ms ] threadCurrent theory is that all mass energy will eventually wind up in black holes - which will then evaporate. All mass energy will then be maximally dispersed in the entropy death of the universe. I think that means the Casimir effect is not destroying mass energy, just dispersing it to a useless state.
Which is not the same as "heat can be dissipated in a 'vacuum' as it is transferred to virtual particles."
spot the difference: "transferred across a vacuum" (to some other object) vs. "dissipated in a vacuum" (to nowhere).
And perhaps corporate_shi11 is using "dissipated in a vacuum" to mean "transfer of internal energy from a hotter body to a colder one across a vacuum"?
shrug - I dunno.
For the Casimir interaction, virtual particles are one way to do the bookkeeping to calculate the force between two objects. One object transfers energy and momentum to virtual particles which in turn transfer the energy and momentum to another object.
Abstraction barriers are very real, immutable and impenetrable by definition.
Consider the 'transformation of energy' ... from mechanical to electrical to acoustical to chemical to potential to kinetic to thermal (end of the line). What is the 'it' that's being transformed?
In one sense all things are 'energetic' so long as they have a velocity (relative to something else). We need to keep an eye on boulders up on hillsides. They're not moving right now ... but their potential energy might be transferred to us, thanks to the equally mysterious 'gravity'.
Yes, the math all seems to work. But we're not quite 'there' yet. Our position is uncertain.
OTOH, from what little I remember from reaction kinetics in chemistry, temperature there is used as absolute value that determines the chance of collision between their molecules and the "activation energy", both of which influence the rate of a chemical reaction. In this space, thermal energy seems like something absolute.
What gives?
Not quite. Potential is defined with an arbitrary basis as you’ve pointed out, but with temperature the basis is not arbitrary: it’s chosen for us, and this value is absolute zero. Taking a temperature difference is not enough to figure out how well a heat engine will work on it.
The only exception to that is gravitational energy, which cannot entirely be localized.
> What is the 'it' that's being transformed?
This is exactly what led to the caloric theory of heat. But nonphysical transfer isn't terribly slippery. Take a rumor. I whisper to someone, who whispers to someone...there is no physical transfer here, merely a transfer of configuration. Transfer of energy, like transfer of genes, is more like that. Nor need it correspond to any particular physical part of a thing, e.g., where is the sarcasm in a sentence?
Locally conserved invariants like energy or momentum don't correspond to any of the categories that we learn in childhood, but that doesn't make them particularly slippery, just unfamiliar.
I also can't see what is particularly wrong with the description of quantum mechanical observations in this article. It looks to me like a good enough description of the idea of research done by the author himself.
Also me: “Questioning the law of conservation of energy”—aaah, a headline clearly intended for sophisticates like myself.
(The article itself is good; I’m just amused at my own reaction.)