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Ask a physicist anything. (7)

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Chalnoth

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Not if the temperature is bellow freezing; Otherwise ice would not exist in the vacuum of space!
No, it actually does! It's just a slow process. And obviously the colder it is, the slower the process.

This is why, for example, if you leave ice in an ice tray in the freezer for long enough, the ice cubes will shrink.
 
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cupid dave

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Cosmology!

Since (x, y, z) is the singularity or point in Space at which all matter would disappear were the Big Bang expansion reversed and Energy requires nor Space and does not exist in Time, is there a repository for ebergy in some dimension still unknown to us?

Because the Law of Conservation of Matter/Energy tells us that this Universe can not disappear materially unless it transmutes back, into an equivalency of Energy, isn't aenergy The First Cause, even "God?"
 
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mzungu

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No, it actually does! It's just a slow process. And obviously the colder it is, the slower the process.

This is why, for example, if you leave ice in an ice tray in the freezer for long enough, the ice cubes will shrink.
What you say is true but the process is so slow as to have little practical meaning. Can you imagine the time it will take for Europa's ice to sublime? Even Black holes evaporate!

This reminds me of Heraclitus' sayings: (excerpts from wicki)

τὰ πάντα ῥεῖ καὶ οὐδὲν μένει.Tà pánta rheî kaì oudèn ménei."Everything flows, nothing stands still."

τὰ ὄντα ἰέναι τε πάντα καὶ μένειν οὐδένTa ónta iénai te pánta kaì ménein oudèn"[That] things that exist move and nothing remains still",

which he expands:πάντα χωρεῖ καὶ οὐδὲν μένει καὶ δὶς ἐς τὸν αὐτὸν ποταμὸν οὐκ ἂν ἐμβαίηςPánta khōreî kaì oudèn ménei kaì dìs es tòn autòn potamòn ouk àn embaíēs"All things move and nothing remains still, and you cannot step twice into the same stream".

If only he knew how right he was when he uttered those words 2500 years ago
 
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Chalnoth

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Two points:
1. Energy just isn't conserved in an expanding universe. Energy conservation only works for systems that don't change in time (or are cyclical). The expansion of our universe breaks that symmetry, and so energy isn't conserved. Nearly all of the energy the exists in matter in our universe was produced during inflation in the very earliest parts of our universe. And that energy was produced from the expansion itself, as opposed to coming from somewhere else.

2. There was no singularity. There cannot have been a singularity, because a singularity is mathematical nonsense. While singularities do exist in our current theories, this is an indication that our theories break down in those areas. Basically, beyond a certain density, our theories just cannot describe what really happened.
 
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Wiccan_Child

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Your premises are incorrect. There is no point in space "at which all matter would disappear were the Big Bang expansion reverse" - the expansion is the expansion of space itself. All of space is expanding, so there's no one place we can point to and say "Aha! It's all moving to this point!". Space expands like a balloon, with each point receding from every other point, but no point being the source of expansion. Everywhere sees everywhere else receding from it.

Because the Law of Conservation of Matter/Energy tells us that this Universe can not disappear materially unless it transmutes back, into an equivalency of Energy, isn't aenergy The First Cause, even "God?"
No. First, conservation laws are, ultimately, just theories. We say that energy cannot be created or destroyed because we've never seen it, and everything we've observed tells us that this law is true. But, nonetheless, it's still possible that the law can be broken, if only in unusual situations. This has happen with other conservation laws: Parity was once thought to be conserved, but the so-called 'weak interaction' violates parity. It's unusual, but it does happen. There's no reason why the same couldn't happen with the conservation of energy.

Second, even if this conservation law were true, it only say that the net energy is constant. A positive hunk of energy that's created at the same time as a negative hunk of energy, would not violate the conservation law, as the net energy hasn't changed. This is how neutrons can decay into a proton and an electron (and an antineutrino) - though the proton and electron have electrical charges, their net charge is zero, thus conserving electromagnetic charge, as per the law of the conservation of charge. In other words, the origin of the universe may well be the spontaneous creation of a finite hunk of 'positive' energy, that occurred at the same time as the creation of an equal amount of 'negative' energy (perhaps gravitational potential).

Third, 'God' is a very specific concept, and nothing is achieved by saying "I don't know the origin of X, but whatever that origin is, I will call it 'God'". The problem with doing that is that you then end up associating the usual traits of 'God' (answering prayers, healing the faithful, etc) to this hypothetical origin, which is silly.
 
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Chalnoth

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What you say is true but the process is so slow as to have little practical meaning. Can you imagine the time it will take for Europa's ice to sublime?
Well, that's a slightly different issue, because Europe has significant self-gravity. So when the ice on the surface of Europa sublimates, you get an atmosphere of water vapor around the planet. The sublimation process will rapidly reach an equilibrium between the water vapor re-depositing on the surface and new water molecules sublimating.

The evaporation of the ice off of the surface, then, is not driven by the speed of sublimation, but is instead driven by the speed at which this atmosphere of water vapor dissipates (atmospheres for spherical bodies are not stable...over time they evaporate, though it can take a while). And once a molecule from Europa's exceedingly thin atmosphere escapes Europa's gravity, it is replaced by a newly-sublimated molecule from the surface of the ice.
 
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mzungu

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You are trying to restrict spacetime into 3 dimensions. This is not possible. Here is something interesting to read: Universe expansion experts win Nobel prize - FT.com
 
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mzungu

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I stand corrected. Such is the beauty of science; A never ending quest for erudition! Thanks

But what of comets who have insignificant gravitational effect?
 
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Chalnoth

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I stand corrected. Such is the beauty of science; A never ending quest for erudition! Thanks

But what of comets who have insignificant gravitational effect?
Well, they are also exceedingly cold....until they approach the Sun...at which point, after a number of orbits, they evaporate!
 
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mzungu

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Well, they are also exceedingly cold....until they approach the Sun...at which point, after a number of orbits, they evaporate!
Yes but what of comets at the oort cloud and kuiper belt? Surely at those temperatures close to naught kelvin and insignificant gravitational forces; Sublimation grinds to almost a halt? Also what of naught kelvin? will ice sublimate?
 
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Ration

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Yes but what of comets at the oort cloud and kuiper belt? Surely at those temperatures close to naught kelvin and insignificant gravitational forces; Sublimation grinds to almost a halt? Also what of naught kelvin? will ice sublimate?

Well, depending on who you talk to, 0K is unreachable because certain quantum principles break down at that temperature.
 
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Chalnoth

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Yes but what of comets at the oort cloud and kuiper belt? Surely at those temperatures close to naught kelvin and insignificant gravitational forces; Sublimation grinds to almost a halt? Also what of naught kelvin? will ice sublimate?
Well, yeah, obviously it's going to be so slow out there that it will almost not happen.

One potential way to understand sublimation if all of the energy is thermal is by examining the thermal distribution of energy, Planck's Law. If all of the energy is thermal, then by following Planck's Law, just by chance, on occasion the atoms on the surface will gain enough energy to break their bonds and leave the ice. But since the amplitude drops off exponentially at high energies, the rate of sublimtation too should drop off exponentially as the temperature drops below the melting point.

Now, in reality, all of the energy accessible is not going to be thermally-distributed. In particular, even far away in the Oort cloud, these objects will be receiving energy in the form of light from the Sun. And so the true rate of sublimation is likely to be higher than the naive estimate from assuming a purely-thermal distribution. Nevertheless, it's got to be a low rate indeed.
 
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mzungu

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Thanks, and for being a good lad I shall reward you with this truly amazing video:
Pendulum Waves - YouTube
 
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Wiccan_Child

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Thanks all for answering my previous question.

Wiccan Child claimed that you could crush say a cup of water into ice if given enough pressure.

I was just wondering if the reverse also held true.
The reverse would be... If you anti-crushed a cup of ice, it would turn into water. Well. It. Well. ordinarily, yes.

(Chalnoth, on account of cider, I require specifics!)
 
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Wiccan_Child

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How do you prove that 2=1 once again, i read it longtime ago in a math book? do you have a clue?
It's impossible, though you can fake it:

a = b

Etc, etc

And therefore, 1=2.

To anyone who concludes this with sufficient acumen, 1 WC point is yours to acquire.

 
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Steffenfield

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a = x [true for some a's and x's]
a+a = a+x [add a to both sides]
2a = a+x [a+a = 2a]
2a-2x = a+x-2x [subtract 2x from both sides]
2(a-x) = a+x-2x [2a-2x = 2(a-x)]
2(a-x) = a-x [x-2x = -x]
2 = 1 [divide both sides by a-x]



I want my WC point now.
 
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Chalnoth

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The reverse would be... If you anti-crushed a cup of ice, it would turn into water. Well. It. Well. ordinarily, yes.

(Chalnoth, on account of cider, I require specifics!)
Haha, well, Wikipedia has a nice phase diagram:
Filehase diagram of water.svg - Wikipedia, the free encyclopedia

From here.

This is pressure vs. temperature. Water only exists in liquid state in the green region, which is above a certain temperature, and for a certain range of pressures. If the pressure is too low, it becomes water vapor. If the pressure is too high, it becomes ice. But below a certain temperature it is either ice or water vapor, and liquid water is no longer possible. The different roman numerals are the different types of ice, which you can read about on the Wikipedia article regarding ice.
 
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