**Ask a monkey a physics question thread**

[OngBonga]

If baudib's mother is fatter than wuf's mother, does that mean baudib will age slower than wuf?

[Renton]

If baudib's mother is fatter than wuf's mother, does that mean baudib will age slower than wuf?

If they're otherwise in the exact same location on earth, yes by a couple of femtoseconds probably. But variation in sea level or crust density at your location would have many orders of magnitude of a larger effect than that fat ass.

[MadMojoMonkey]

If baudib's mother is fatter than wuf's mother, does that mean baudib will age slower than wuf?

Assuming both baud and wuf are staying quite close to their mothers, and their mothers aren't too close to each other, then yeah, I guess.

Given the high probability that they both spend an inordinate amount of time near each-other's mothers, though.. it's probably a wash.

As Renton correctly pointed out, though, the effects would be so slight as to be immeasurable.

***
I don't have a 'rule of thumb' for mass-based changes in the relativistic factor. For velocity-based changes, effects are usually immeasurable for speeds below about 0.2c or ~60,000 km/s (~134,000,000 mph). At that speed, The relativistic factor is ~1.0206. This means that time is dilated by ~2.06%, space is contracted by that factor in the direction of motion, and mass is increased by that factor.


fraction of c || relativistic factor
0.1 || 1.0050
0.2 || 1.0206
0.3 || 1.0483
0.4 || 1.0911
0.5 || 1.1547
0.6 || 1.2500
0.7 || 1.4003
0.8 || 1.6667
0.9 || 2.2942
0.99 || 7.0888
0.999 || 22.3663
0.9999 || 70.7124

You can see that the relativistic factor grows slowly until ~0.5c, and then rapidly above 0.8c.
Notice that something traveling at 99% the speed of light can cover over 7 light-years of distance (in an outside observer's reference frame) in about 1 year's time (in the traveler's reference frame). This is not a violation of the speed of light, it is the consequence of said speed limit.

[OngBonga]

I already knew the answer to my question, I just thought it was funny. You guys are too serious. I guess you're all aging slower than me.

[Eric]

I have questions about my Einstein book. Some of them aren't related to quantum physics, should I start a new thread?

[MadMojoMonkey]

I have questions about my Einstein book. Some of them aren't related to quantum physics, should I start a new thread?

I think this thread is fine, but if you want a more specific conversation on a topic, then a new thread is fine, too.

[Eric]

I think this thread is fine

Ok, cool. Like I said, Einstein by Walter Isaacson has a lot to think about.


We shine a light into space. I get on a spaceship going in the same direction at 10k miles per second.


The light is moving away from both me and the earth at 186k miles per second, right?
We're not used to thinking this way, we're used to thinking of something moving away from me at just 176k (186 - 10).
The key is time, right? My relative time is different than the earth's relative time.


Page 119 talks about sound being constant at 770 miles per hour. How is sound the same as light and how is it different?

[MadMojoMonkey]

We shine a light into space. I get on a spaceship going in the same direction at 10k miles per second.

(A)The light is moving away from both me and the earth at 186k miles per second, right?
We're not used to thinking this way, we're used to thinking of something moving away from me at just 176k (186 - 10).
(B)The key is time, right? My relative time is different than the earth's relative time.

A) Yes, what you describe with (186 - 10) is called Galilean Relativity.
I'll use 186k mps as the approximation for our discussion.

B) The key is both time and space. The distances (outside your ship) in your direction of travel are shorter.
It is the combined effects of both time dilation and space contraction that contribute to the constant speed of light.

(Nicely put, OngBonga.)

Page 119 talks about sound being constant at 770 miles per hour. How is sound the same as light and how is it different?

Actually, this is a difficult post because we're touching on a lot of concepts that a freshman course in physics would spend weeks on. Please bear with me if I'm long winded and feel free to follow up on parts where I'm terse.

***
Part 1: What do we mean by constant?

The speed of sound is not constant. It can be treated as constant at 770 mph for most airplanes, though. This a close approximation for the speed of sound at STP (Standard Temperature and Pressure). Variations in the chemical composition (primarily humidity, on Earth) of the air or the ambient air pressure or any average flow (wind) will affect the speed at which sound waves travel.

Both sound and light move at different speeds in different mediums.
What's that I said? Light moves at different speeds?
Yes.

The "constant" speed of light is the maximum speed in vacuum. Light travels more slowly when it passes through a medium. E.g. As light passes through a pane of glass with a refractive index of 1.5, the light travels at a speed of c/1.5 = (2/3)*c ~= 124k miles per second. As light passes through air at STP, which has a refractive index of 1.000293, the light move more slowly, at a rate of c/1.000293. This is ~55 mps slower than its speed in vacuum.

The lowest possible refractive index is 1. There is no material through which light moves faster than c.

When we talk about the "constant" speed of light, we're talking the speed in vacuum and about what you described in terms of relative motions of observers.

The important point here is that the speed of sound is relative to particles in a region interacting with each other. Any variations which increases or decreases the frequency or violence of particle collisions is going to alter the speed of sound.
The speed of light is a property of the electromagnetic fields. The EM fields exist everywhere in the universe (so far that we've checked) and are not merely restricted to regions where there is "stuff."

***
Part 2: Similarities between light and sound

Sound is like light in that both propagate as waves. This means they follow the same basic mathematics as far as being solutions to the wave equation.

The wave equation explicitly states the relationship between the derivatives of a function w.r.t. space and time. It predicts how any function will evolve through space over time, given the properties of the restorative forces and dissipating forces.

***
Part 3: Differences between light and sound

The most striking difference is what is waving.

A special note is that when we talk about the constant speed of light in vacuum, we are talking about waves propagating through a region with no dissipating forces. This gives the waves a theoretically infinite range.

There is no analogue for sound waves. Sound waves propagate through a medium of particles which dissipate the wave's energy by creating heat, inelastic deformations, etc.

Sound is an alternating region of pressure in a medium. In air, it is the statistical summary of all the molecular interactions which result in particles exchanging energy. Sound is a longitudinal wave, meaning that it's action is along it's direction of travel.

Light is an electromagnetic wave. What is waving are the electromagnetic fields. These fields are intangible in the sense that they are not made of atoms. EM waves are transverse waves, meaning that the action is perpendicular to the direction of travel.

[OngBonga]

Oooh I think I know some of this. I don't care if I don't, I'm answering.

The key is time, right? My relative time is different than the earth's relative time.

Yeah, which also means your perception of space is different to an observer on Earth. As time expands, space contracts. You measure the light travelling at c, which would lead you to think that I would measure it from Earth at c+10km/s, which defies logic. But you measure the distance differently to someone on Earth, a direct consequence of the difference in time. You would measure the distance between Earth and beam differently (shorter) than someone on Earth, and that accounts for the extra 10km/s in apparent speed above c.

Or something like that.

[Eric]

As time expands, space contracts.

But you measure the distance differently to someone on Earth, a direct consequence of the difference in time. You would measure the distance between Earth and beam differently (shorter) than someone on Earth, and that accounts for the extra 10km/s in apparent speed above c.

Right, it is starting to make sense.
If we take the http://www.einstein-online.info/spotlights/Twins traveling twins example to an extreme then we can say that I age slower than people on earth because I'm moving closer to the speed of light.
As such, I could take a measurement at 59 seconds while someone on earth does it at 60.
Still trying to get my head around this.

[MadMojoMonkey]

Right, it is starting to make sense.
If we take the http://www.einstein-online.info/spotlights/Twins traveling twins example to an extreme then we can say that I age slower than people on earth because I'm moving closer to the speed of light.
As such, I could take a measurement at 59 seconds while someone on earth does it at 60.
Still trying to get my head around this.

That link offers a poor explanation that ignores the fact that we can take out the acceleration entirely and still predict the time dilation.

Assume we have 3 clocks. One on Earth, the inertial frame. Another is already moving at speed past Earth, and happens to be perfectly synchronized with Earth as it passes. The third clock is going in the opposite direction of the 2nd. It passes the 2nd some distance away, and at that time, those 2 clocks happen to be perfectly synchronized.

Now, the 3nd clock passes the first clock on Earth some time later and we STILL note that the clocks are not synchronized, even though we have completely eliminated any accelerating reference frames.

The actual answer to unravel the paradox is to understand that spacetime paths have different lengths, and that's enough to desynchronize the clocks. The "inertial" clock on Earth has a theoretical spacetime path which moves only in time, but not in space. The other clocks move in both time and space. The magnitude of the length of the spacetime path is what determines a clock's tickrate.

(And again, we're talking about the imaginary, internal clocks which mediate all interactions. Yes, slowing down all the interactions slows down the macroscopic clock, but it's literally that time flows at a different rate, and nothing to do with clocks, as such.)

[OngBonga]

Still trying to get my head around this.

So am I. Time dilation fascinates me. I'm not for a minute pretending to understand it. I've been trying to for years, and probably never will.

[OngBonga]

(Nicely put, OngBonga.)

In fairness, there's a greater than zero chance that I've just reworded something you said earlier in this thread. I'm sure we've discussed time dilation already on more than one occasion.

[OngBonga]

It should be noted that no matter how fast you're going, you will never measure c at more than it should be. You will simply assume that others are measuring it as faster, when actually they're measuring it travelling at the same speed over a longer distance. It's space, and therefore time, that we disagree on, not c.

[MadMojoMonkey]

In fairness, there's a greater than zero chance that I've just reworded something you said earlier in this thread. I'm sure we've discussed time dilation already on more than one occasion.

As if I'm doing anything different? Mostly, I'm repeating what textbooks and professors have shown me.

OK, it's a little different.
The main difference between you and me is the math and the body of experiments that I've done to test the statements.

I think not everyone wants to get the degree I have, nor should they.
The more armchair physicists out there who have a layman's interest in the field, the better, IMO.

It should be noted that no matter how fast you're going, you will never measure c at more than it should be. You will simply assume that others are measuring it as faster, when actually they're measuring it travelling at the same speed over a longer distance. It's space, and therefore time, that we disagree on, not c.

I can't speak of what anything "should" be; I can only relate what has been observed.
What I observe and what I assume are (hopefully) very distinguishable to me.

@bold:
They're measuring it traveling at the same speed over a different distance in a different amount of time.

"It's space, and therefore time"
At first, I was all, "grrr it's spacetime!" but then I was like, "I guess that's what he said."

The point of GR is that we can agree on spacetime, no matter our relative velocities or local gravitational fields.

[Eric]

Sometimes I think I get it.

Other times I feel totally lost.

It is amazing that Einstein figured this stuff out.

[MadMojoMonkey]

Sometimes I think I get it.

Other times I feel totally lost.

It is amazing that Einstein figured this stuff out.

I spent hours trying to weed through the YouTubes to find a brief, but concise explanation of the Michelson-Morley experiment and to put it in the context of one of the most successful "failures" in the history of modern physics.


This is the historical story of the experiment that showed that something is undeniably wrong with Galilean Relativity:

It's part 1 of 3. They're ten minutes each.

WARNING:
The production looks like the kind of educational video I was shown in grade school. I'm guessing it was made in the 70s.
If you are the kind of person who doesn't like that production style, you will nod off and fall asleep on this one. Do not click.

That said. This is an excellent use of 30 minutes for anyone who is struggling with getting their foot in the door to understand General Relativity. It gives the historical context, with a college professor bookending the presentation. That professor, frankly, nails it. I'm going to watch the next set of 3 vids in this series right now.

[OngBonga]

"It's space, and therefore time"
At first, I was all, "grrr it's spacetime!" but then I was like, "I guess that's what he said."

Can I call it timespace?

[Renton]

This is probably an easy one for you.

As I'm rinsing a hot frying pan with cold water, the handle feels hotter right away. The pan is made out of steel (I guess), and the handle is just an extrusion of the metal, with no plastic cover or anything. The cooking surface is coated with teflon. What explains this effect?

[MadMojoMonkey]

This is probably an easy one for you.

As I'm rinsing a hot frying pan with cold water, the handle feels hotter right away. The pan is made out of steel (I guess), and the handle is just an extrusion of the metal, with no plastic cover or anything. The cooking surface is coated with teflon. What explains this effect?

Note that I make stark contrast between temperature and heat
Temperature - a bulk-scale measure of micro-scale kinetic energy. Temperature is measured in Kelvin or degrees C.
Heat - the flow of temperature in space and time. Heat is a form of work, and therefore energy, and is measured in Joules.

Interestingly, heat is yet another physical process which is modeled by the wave equation.

***
Thermodynamics says that heat always flows spontaneously from hot to cold. Spontaneously means that no outside force or energy needs to be applied, this flow of temperature just happens.

Visually, this is due to particle collisions in the medium resulting in the particles exchanging some energy. Statistically, after many exchanges of energy, the particles will have more similar energies than prior to their interactions. They tend toward the mean.

So...
The handle should begin to decrease temperature as soon as the temperature differential between the pan and the handle makes the pan colder or the handle hotter.

***
However, you're not asking about the temperature of the handle. You're asking about the heat that your hand feels on the handle. This is a different thing which involves the rate of flow of temperature between the pan handle and your flesh, then through your flesh to your pain receptors. Furthermore, it involves the saturation of pain receptors in your hand which triggers a sense of intensity of the heat.

If you touch the hot handle and immediately remove your hand, you may notice a couple of things:
1) Your hand is well removed from the handle before you begin to feel the temperature change.
2) The duration of the feeling is longer than your hand was on the pan's handle.

[EDIT]It occurs to me that your hand on the handle acts as a heat sink of a kind. It is probable, though I can't recall having observed it myself, that the temperature which your hand absorbs on first contact with the handle causes the handle's cooling to increase, which draws a bit of temperature from the pan.[/EDIT]

I would experiment with holding the pan for the same amount of time, but not dousing it in water.
Don't hurt yourself, obv.

My hypothesis is that you will find the same sensation of the handle gradually warming.

[Renton]

The issue though is that the dousing with water seemed to change the way I felt the heat. The pan felt quite warm when I was holding it, but within 2-3 seconds of running the water onto it, it became almost too hot to hold. It's like the water somehow caused the pan to become a faster heat conductor, which makes no sense to me.

edit: The heat is definitely not evenly distributed in the pan at the moment I start running water on it. The bottom of the pan is likely many times hotter than the handle since it was on the burner. That is probably very relevant to this.

[MadMojoMonkey]

The issue though is that the dousing with water seemed to change the way I felt the heat. The pan felt quite warm when I was holding it, but within 2-3 seconds of running the water onto it, it became almost too hot to hold.

I get you. My hypothesis is that the sensation is more to do with heat flow in your hand than with heat flow in the pan.

I have not experienced the sensation as you describe it, so I can't really explain it. If you tell me you did the experiment I described above and get the same results, then I'll certainly be discarding my hypothesis and thinking more deeply about the question.

It's like the water somehow caused the pan to become a faster heat conductor, which makes no sense to me.

The rate of heat flows much more readily from the pan to water than pan to air. In that sense, the conduction is faster.

I'm sure that the thermal conductivity of the metal is ultimately a function of it's own temperature. I doubt that there is significant change in the temperature ranges we're dealing with. (I'm thinking molten aluminum would likely have a different rate than solid aluminum.)

edit: The heat is definitely not evenly distributed in the pan at the moment I start running water on it. The bottom of the pan is likely many times hotter than the handle since it was on the burner. That is probably very relevant to this.

The main reason the handle is a different temperature is due to radiation and convection of the heat between the flame and handle. In a vacuum, the lack of air to transfer heat away from the pan would make the entire pan nearly the same temperature. Obviously, if you keep pumping energy into the pan, then it wont stay a pan for long.

It's complicated if the pan isn't empty, obviously. A pan boiling water will have a sharp temperature gradient on the bottom of the pan. The outside surface is exposed to flame at 1,950 C (assuming the fuel is methane aka natural gas, burning in air), but the inside surface is exposed to water at 100 C (assuming the water is boiling).

The temperature of the handle is difficult to guess for an arbitrary pan with arbitrary contents.

Based on my job working at an espresso shop, human skin can't maintain contact with metal over ~135 degrees F for more than about a second. (There's a thermometer in the aluminum carafe used to steam the milk at most shops. Obv. I experimented on myself and thermal tolerance in my fingers.)

I'd be shocked if you're touching metal over 140 degrees F for any duration w/o first degree burns (redness and sensitivity).

[OngBonga]

Condensation of steam as it makes contact with the handle?

[OngBonga]

As a liquid molecule boils into a gas, it expands, and in doing so, it absorbs heat (cooling anything it comes into contact with - lick the back of your hand). On the other hand, as a gas molecule condenses into a liquid, it radiates heat. Thus, as water hits the hot pan, it creates steam, which then comes into contact with the relatively cool pan handle, causing condensation, which in turn causes heat transfer from steam to pan handle.

Can I have a gold star please?

[MadMojoMonkey]

As a liquid molecule boils into a gas, it expands

The molecule doesn't change size.
It acquires enough energy so that its own internal energy of vibration is greater than the energy of the intermolecular bonds. When this occurs it becomes highly likely that the molecule will vibrate rigorously enough to escape the "sphere of influence" of its bonded neighbor. In breaking the bond, it converts some of that energy into kinetic energy, which it caries away.

The reduction in temperature due to evaporation is the combined effect of the broken bond and the fact that the molecule which broke the bond was one of the hottest molecules in the fluid, leaving cooler molecules behind.

and in doing so, it absorbs heat (cooling anything it comes into contact with -

It absorbs temperature, which it caries away. The movement of temperature is heat.
nit picked.

[EDIT]Wait... cooling anything it comes into contact with? NO.
Cooling the fluid from which it evaporated. YES.[/EDIT]

- lick the back of your hand). On the other hand,

Lick the back of my hand on the other hand?
I'll just lick both to be sure.
Ewwwwww. Where have they been?!

as a gas molecule condenses into a liquid, it radiates heat. Thus, as water hits the hot pan, it creates steam, which then comes into contact with the relatively cool pan handle, causing condensation, which in turn causes heat transfer from steam to pan handle.

This proposition says that
the water being converted to steam coming off the pan then back into water on the pan's handle
is more effective than transferring heat through the solid metal - in a relatively straight line.

I don't think the geometry of this problem would favor this explanation which requires two changes of phase in the transfer medium (water - steam - water).

I'm not denying that this could happen to some higher order effect. I mean... it could make a difference in the 3rd or 6th decimal place of the temperature of the handle, but I doubt it is relevant for this experiment.

Can I have a gold star please?

How about a moon instead?

[Renton]

I'll do your experiment next time I cook. I think I know what it feels like to hold something that's hot for a little too long, and this really seemed different from that. That said I know that doesn't sound very scientific.

ong: yeah I thought the heat of vaporization of the water maybe had something to do with it also. But I don't know why that would make the pan feel hotter, instead of immediately cooler.

edit: Just wanted to add that the pan didn't get so hot that I couldn't hold it, just noticeably warmer. I'm sure it wasn't hot enough to burn me.

[OngBonga]

ong: yeah I thought the heat of vaporization of the water maybe had something to do with it also. But I don't know why that would make the pan feel hotter, instead of immediately cooler.

Vapourisation cools, so the water turning to steam will have a cooling effect on the pan where the water strikes and turns to steam. But if steam is then coming into contact with the handle and condenses to water, it will have a warming effect - it's the polar opposite of evaporation. Maybe the warming effect is not enough to be noticable, and that another explanation is necessary. But I can't think of another reason why cold water on a hot pan would warm the handle.

[OngBonga]

And yes mojo, I realise that an expanding gas does not mean the molecules are actually getting bigger, that was sloppy language on my part. An expanding gas as I understand it is one in which the molecules have an increasing average distance between each molecule, or something like that anyway.

[MadMojoMonkey]

The conclusion that condensation adds temperature in the time-opposite way that evaporation removes temperature deserves some respect, actually.

And yes mojo, I realise that an expanding gas does not mean the molecules are actually getting bigger, that was sloppy language on my part. An expanding gas as I understand it is one in which the molecules have an increasing average distance between each molecule, or something like that anyway.

OK, now you've earned it.



Unfortunately... the more I think about this idea, the less I like it. The steam is passing through room temperature air on its path from the pan to the handle. It's going to lose a lot of temperature on that journey due to turbulent flows and mixing of steam with the air in the room, even over short distances.

Spraying the metal handle with a jet of steam would definitely rapidly increase the temperature to 100 C. Perhaps a bit more, depending on the pressure in the steam line.

***
I'm curious over the reproducibility of this phenomenon, Renton.

The thermodynamics is clear on the spontaneous flow of heat from hot to cold, such that the system tends toward equilibrium. It's buried in the 2nd Law of Thermodynamics... with a good bit to say about entropy increasing during this process.

This makes it terribly unlikely that the heat is flowing from cold to hot. It has to be "pumped" to do so. This is where the term "heat pump" comes from, which is ubiquitous in thermodynamics.

If the experiment I suggested proves wrong, consider if this explanation fits your observations:
The cool handle was being heated by the hot pan while you were grabbing and transporting the pan to the sink. The heat flow was already initiated by the disparity in temps. When you added the water, the previous flow took a moment to respond, during which time, the handle noticeably increased in temperature by a few degrees.

The water did not initiate the flow of temperature to the handle, but was coincidentally timed with said temp. increase.

[Eric]

Is there methane based life on Titan that eats hydrogen?

[MadMojoMonkey]

Is there methane based life on Titan that eats hydrogen?

Dunno.

There is currently no known evidence of extra-terrestrial life. There is a bit of fuzziness there in that amino acids have been found in (I believe) comets and asteroids.

wikipedia "Life on Titan"
If it's there, it's going to be exotic to say the least. We know basically nothing about the origins of life. Our direct evidence only suggests that it happened on Earth (or near enough to Earth and was deposited here).

It would be a huge boon to biology to have another example to study.
Niel DeGrasse Tyson has said that he would be excited just to find DNA anywhere but Earth.

Some researches found a possible cell wall structure which might work.
It's a computer model of a structure with similar properties to a cell wall. It has not been observed in nature (as far as I can tell from the article).

It sounds like this is only one piece of the puzzle. A cell wall is important insofar as it protects the rest of the cell. We still need a model (if not example) of the internal chemistry/biology that makes up the cell.

[chemist]

Is there methane based life on Titan that eats hydrogen?

Dunno.

There is currently no known evidence of extra-terrestrial life. There is a bit of fuzziness there in that amino acids have been found in (I believe) comets and asteroids.

wikipedia "Life on Titan"
If it's there, it's going to be exotic to say the least. We know basically nothing about the origins of life. Our direct evidence only suggests that it happened on Earth (or near enough to Earth and was deposited here).

It would be a huge boon to biology to have another example to study.
Niel DeGrasse Tyson has said that he would be excited just to find DNA anywhere but Earth.

Some researches found a possible cell wall structure which might work.
It's a computer model of a structure with similar properties to a cell wall. It has not been observed in nature (as far as I can tell from the article).

It sounds like this is only one piece of the puzzle. A cell wall is important insofar as it protects the rest of the cell. We still need a model (if not example) of the internal chemistry/biology that makes up the cell.

Going back to an old topic.
"If it's there, it's going to be exotic to say the least."
"Niel DeGrasse Tyson has said that he would be excited just to find DNA anywhere but Earth."

If it is so exotic why would it necessarily have DNA?
Could something exotic without DNA still be considered a life form?

[MadMojoMonkey]

Going back to an old topic.
"If it's there, it's going to be exotic to say the least."
"Niel DeGrasse Tyson has said that he would be excited just to find DNA anywhere but Earth."

If it is so exotic why would it necessarily have DNA?
Could something exotic without DNA still be considered a life form?

The first question answers itself. It would be hugely unlikely for it to have DNA if it isn't something that the universe or periodic table favors. If it could be shown that the DNA-having stuff originated from somewhere else, that's huge. (If it turns out it came from here and contaminated to somewhere else, then that's meh.) If it turns out that there is non-DNA-based life, then that's huge.

The second question is probably better answered by a biologist, but my gut says that if it can argue that it is alive, then it's probably best to not argue back that it isn't.

[chemist]

The first question answers itself. It would be hugely unlikely for it to have DNA if it isn't something that the universe or periodic table favors.

That is what I thought and why I was confused by the Niel DeGrasse Tyson statement which I thought was irrelevant to the original answer. Sure non earth originating DNA is interesting but let's not rule out non DNA exotic life.

if it can argue that it is alive, then it's probably best to not argue back that it isn't.

Good Answer.
Unless it is smaller than us, then we could argue with it.
I'd argue with a little monkey but think twice about arguing with a big Gorilla, (unless it was remotely in an online forum).



I'm glad black holes are so far far away that we can't yet measure their change in gravity as they consume galaxies,
though a little concerned that you show the milky way in your example.

(our great great ... great ... great ...great great grandchildren should definitely have a referendum to leave the milky way before that hole takes over)
Yeah I know you're going to point out the sun will have expired long before that happens.

[OngBonga]

It's going to lose a lot of temperature on that journey due to turbulent flows and mixing of steam with the air in the room, even over short distances.

Understood, but if it's still steam and not water when it comes into contact with the handle, it's still not lost enough heat to be under 100c. It shouldn't matter how hot the steam is when it comes into contact with the handle, provided it is steam. It will release heat when it condenses, and anything it is in contact with will be the first to benefit from that heat. The question is if that heat is significant enough to account for the noticable increase in temperature.

I feel like it must be, because logically one would expect the handle to become cooler, not warmer, as the metal pan loses heat to the water. If we can't find another method of warming, then are we to assume it's a psychological thing? That it is a question of our perception of heat? That seems even more exotic than my proposal.

[MadMojoMonkey]

Understood, but if it's still steam and not water when it comes into contact with the handle, it's still not lost enough heat to be under 100c. It shouldn't matter how hot the steam is when it comes into contact with the handle, provided it is steam.

"Provided it is steam."
It isn't.

(Half a gold star for the phrasing, though. You identified your assumption explicitly.)

Clouds are not 100 C; they are made of water vapor and not steam.

I think it's time for another set of (annoying?) scientific definitions:
Steam - Invisible; temp is at least 100 C at 1 atmosphere of pressure
Water vapor - Visible; temp is no more than 100 C at 1 atmosphere of pressure

Steam is transparent in the visible spectrum. What you see is water vapor, which is cooler than 100 C.

There is enough kinetic energy in the air to hold tiny molecules from falling, even if the tiny molecule technically is dense enough to precipitate from the fluid. Dust from Africa makes its way to South America.

It will release heat when it condenses, and anything it is in contact with will be the first to benefit from that heat. The question is if that heat is significant enough to account for the noticable increase in temperature.

Excellent!

I feel like it must be, because logically one would expect the handle to become cooler, not warmer, as the metal pan loses heat to the water. If we can't find another method of warming, then are we to assume it's a psychological thing? That it is a question of our perception of heat? That seems even more exotic than my proposal.

Not assume -> hypothesize and test.

[OngBonga]

I think that in the 2-3 seconds that it takes for the handle to warm noticably, some of the water is turning into steam as it makes contact with the very hot surface of the pan. This in turn saturates the surrounding air, warming it and causing locally high humidity, resulting in a decrese in aerial condensation of steam. This will cause a reasonable amount of steam to travel in all directions as it expands (or diffuses?). Any steam that comes into contact with the cool metal handle will quickly condense into water, thus releasing heat.

This explanation doesn't seem all that exotic. Granted, I have no idea how much heat is released when a steam molecule condenses into water. But when I'm filling my lighter up, the liquid gas that escpaes into the air and evaporates causes a significant cooling to the point it freezes the bottom of the lighter and cools the fingers where it holds the lighter to the point it almost hurts. I can see condensation having the opposite effect to this.

[MadMojoMonkey]

I think that in the 2-3 seconds that it takes for the handle to warm noticably, some of the water is turning into steam as it makes contact with the very hot surface of the pan. This in turn saturates the surrounding air, warming it and causing locally high humidity, resulting in a decrese in aerial condensation of steam. This will cause a reasonable amount of steam to travel in all directions as it expands (or diffuses?). Any steam that comes into contact with the cool metal handle will quickly condense into water, thus releasing heat.

This explanation doesn't seem all that exotic.

This could be tested with a 2nd pan. Allow the steam from the first pan to condense on the handle of the 2nd pan and measure the increase in temp on the 2nd pan's handle.

Granted, I have no idea how much heat is released when a steam molecule condenses into water.

The heat of vaporization of water is:
H_v(water) = 2,260 J/g

If you have 1 gram of steam at 100 C, you will release 2,260 J of energy by condensing that gram to water at 100 C.

If the steam has already converted to water vapor, then the energy cost to change states has already been spent.

[OngBonga]

I remember watching a documantary about how the Chinese built the Tibet Railway. They had one serious problem up on the tundra, and that was that the top inch or two of the ground would not remain frozen all year round, meaning it would compromise the structural integrity of the track. They solved this problem by using a couple of solutions, but the key one was to refridgerate the underlying rock by exploiting the evaporation/condensation cycle. I can't remember what liquid they used, but they would put tubes upright into the ground with a liquid trapped inside. It would settle in the bottom, and evaporate, rising to the top as a vapour, where it would condese, and settle at the bottom as a liquid. Ths cycle would transfer heat from the ground to the atmopshere, reducing the local ground temperature just enough to keep it frozen all year round.

Them Chinese are smart fuckers.

[MadMojoMonkey]

I can't remember what liquid they used, but they would put tubes upright into the ground with a liquid trapped inside. It would settle in the bottom, and evaporate, rising to the top as a vapour, where it would condese, and settle at the bottom as a liquid. Ths cycle would transfer heat from the ground to the atmopshere, reducing the local ground temperature just enough to keep it frozen all year round.

The liquid is ammonia.

Yes, this is an interesting bit of engineering. They have oxygen producing factories along the route, since it is so far above sea level.
Fascinating!

***
I just want to be clear that I absolutely concur with you that condensation deposits temperature.

I'm merely skeptical about the extent of the effect in the particular question that Renton posed.

[MadMojoMonkey]

But when I'm filling my lighter up, the liquid gas that escpaes into the air and evaporates causes a significant cooling to the point it freezes the bottom of the lighter and cools the fingers where it holds the lighter to the point it almost hurts. I can see condensation having the opposite effect to this.

Sounds like you're talking about a butane lighter (as opposed to a Zippo-type, which generally burns Naptha). The butane is a gas at STP, so it must be contained in a pressure vessel.

The butane is held above atmospheric pressure, so that it can be stored as a liquid. The liquid is much more dense than the gas, so this method allows much more efficient use of volume.

When you release that pressure, the temperature of the fluid drops according to the ideal gas law.
PV = nRT

If I simplify this to mere expansion, and ignore the fact that the number of particles in the pressure vessel is changing, then I get the result by re-writing the equation as this
P/T = nR/V
then I acknowledge that nR/V is the same in the before and after pictures, so I can equate (P/T)_before = nR/V = (P/T)_after.

P_1/P_2 = T_1/T_2

where P_1 is the starting pressure, P_2 is the ending pressure, T_1 is the starting temperature, and T_2 is the ending temperature.
Which means that if the pressure goes down by X%, then the temperature goes down by X%, and vise-versa.

***
It gets a bit ugly and confusing for the purposes of this post to acknowledge that the number of particles in the pressure vessel goes down, too. It's hard to make generalizations with the added two variables.

I could be persuaded to do a full write-up of a hypothetical case of butane released from a pressure vessel. Then we could compare actual values of the temperature change due to the pressure change, then compare that temp change to the temp change caused by subsequent evaporation.

I.e.
If I have a full butane container with X grams of butane, and I spray 0.5 grams of butane on a surface...
What is the temperature of the butane as it is deposited on the surface?
(Note that this will vary over time as the pressure changes during the spraying.)

What is the temperature of the last butane molecule to evaporate?

These two question should indicate the initial temp and final temp of both the sprayed butane and the deposited butane.

(These questions will require some calculus to solve.)

[OngBonga]

I'm merely skeptical about the extent of the effect in the particular question that Renton posed.

I am more skeptical now than I was at the beginning of this discussion.

Still, steam or vapour condensing into water will release heat. It's not the direct convection from the steam that I'm suggesting heats the handle up, it's the indirect convection thanks to the condensation. That condensation is present, regardless of whether we're talking about steam or vapour.

I think the clue to look for would be tiny water droplets on the pan handle. That would certainly demonstrate that condensation is happening, even if it doesn't tell us the extent to which it heats the handle.

As for if life exists elsewhere, well that's a question we don't know the answer to that is also ridiculously easy to answer, imo.

Most probably indeed. I dunno about Titan, obviously. But the universe? Sure, I'd be happy to bet all the money in the world on that. (It helps that it can only be proven true, and never be proven false! I will either win the bet, or spend my life never losing!)

[OngBonga]

Also, yes it was indeed ammonia. I went and watched the documentary again. Knowing how to refridgerate something without power could be a useful bit of knowledge!

[MadMojoMonkey]

Also, yes it was indeed ammonia. I went and watched the documentary again. Knowing how to refridgerate something without power could be a useful bit of knowledge!

The ancient Egyptians had A/C in their homes (of a sort). Probably just the wealthy homes, not sure at all.

They would dig long slanted underground tunnels from their homes toward the nile. About halfway there, they would dig out a small cistern and then continue digging forward and back up. This made a V-shaped tunnel, with a small pool of water at the bottom.

The difference in air pressure from the river side to the house side would drive an air flow which was cooled by passing underground, and evaporating the pool at the bottom.

I'm not sure if they did anything to keep the air flowing into the house. (I didn't fully understand the mechanism which keeps the air flowing in one direction.)

[OngBonga]

It's taken me longer than it should to realise you mean air conditioning rather than alternating current haha. I was thinking wtf, they had alternating current back then? I thought that was Tesla's work!

I'm thinking that they probably don't need to do anything to ensure the air flow is consistent.

In a hot arid environment, the river will be evaporating relatively quickly. This will cause a cooling of the surrounding air, which will mean the air around the river itself is denser (and more humid) than the air above the plains. This will mean there is a constant outward air pressure, which is exploited by their tunnels. The air moves up the tunnel to the pool, where it evaporates the water, cooling and humidifying the air, which continues upward thanks to the lower air pressure at the top of the tunnel.

Simple but very clever.

[MadMojoMonkey]

I'm thinking that they probably don't need to do anything to ensure the air flow is consistent.

In a hot arid environment, the river will be evaporating relatively quickly. This will cause a cooling of the surrounding air, which will mean the air around the river itself is denser (and more humid) than the air above the plains. This will mean there is a constant outward air pressure, which is exploited by their tunnels. The air moves up the tunnel to the pool, where it evaporates the water, cooling and humidifying the air, which continues upward thanks to the lower air pressure at the top of the tunnel.

Simple but very clever.

Humid air is less dense than dry air.

clouds

Care to reformulate your hypothesis?

[OngBonga]

Hmm. I assumed (I know you love that word) that the presence of water vapour in the air would make it more dense, not less.

Well cooler air is certainly denser than warm air, which is why hot air rises.

Ok, the increase in air density above the river caused by the cooling effect of evaporation will need to be more than sufficient to account for the reduction in density caused by the increase in humdity. Do your not-assuming thing. Numbers and whatnot.

[OngBonga]

Ok so I've thought this through for a minute or two while smoking.

Water evaporates from the river, cooling the air. The cooling makes the air denser, but the humidity makes the air less dense, so there is a battle. I propose that the humidity will tend to rise perpendicular to the ground, as it is less dense, while cool less humid air moves outward, parallel to the ground, sucked into a lower pressure area away from the river. Warm dry air will be sucked in at a 45 degree angle to continue the cycle.

[MadMojoMonkey]

Hmm. I assumed (I know you love that word) that the presence of water vapour in the air would make it more dense, not less.

I don't know of anyone who got this right the first time they guessed. Myself included.

I don't hate assumptions. I use them all the time.
(The ideal gas law is an assumption. There is no gas that acts exactly like an "ideal" gas.)

I just love it when the assumptions are explicitly stated, if not implied by the question.

Well cooler air is certainly denser than warm air, which is why hot air rises.

Bless you for the wording. I have a pet peeve with the phrase, "hot air rises." There is no mystical anti-gravity power that makes heat rise. It's the cooler, denser stuff that is pulled down by gravity, displacing the warmer stuff.

In fairness, even other physicists think I'm going overboard with nit-picking on this.

Ok, the increase in air density above the river caused by the cooling effect of evaporation will need to be more than sufficient to account for the reduction in density caused by the increase in humdity. Do your not-assuming thing. Numbers and whatnot.

lol

Surface water temp / ambient air temp and humidity / wind
I think it's tractable with some assumptions.

I'm actually curious how much cooler it is. Anecdotally... Riding a motorcycle across a river valley is a noticeable shift in temp and humidity while I'm in the lowlands between the river bluffs.

Ok so I've thought this through for a minute or two while smoking.

Water evaporates from the river, cooling the air. The cooling makes the air denser, but the humidity makes the air less dense, so there is a battle. I propose that the humidity will tend to rise perpendicular to the ground, as it is less dense, while cool less humid air moves outward, parallel to the ground, sucked into a lower pressure area away from the river. Warm dry air will be sucked in at a 45 degree angle to continue the cycle.

IDK about the 45 degree angle. It could just come in from the side, above the cool air moving out. Wind is going to alter the angle, at any rate. The atmosphere is fairly thin sheet in cross-section.

Other than that... bravo, sir.

The splitting of the humidity and the cooled air seems like a good model to work with. I can try to make some very loose approximations of the effect, but fluid dynamics is intense. Most fluid dynamics is done computationally. The people who work on this generally have a dozen or so computers working on a single problem for days or weeks just to get a result. The result is sensitive to the software settings, so it can take a while to get the result you want.

I'm saying... I can give a "back of an envelope" idea of this, but it's probably going to be so vague as to be common sense.
That's my hedge.
We'll see.

[MadMojoMonkey]

I'm saying... I can give a "back of an envelope" idea of this, but it's probably going to be so vague as to be common sense.
That's my hedge.
We'll see.

I decided to look for the source of this model before I went on to speculate over our hypothesis. This is the only thing I found that seems to match the description that I gave. It has no references, and is of dubious authority.

http://www.i4at.org/surv/aircond.htm

Turns out, the cooling shaft is only half the story.

It's hard to make sense of the description in #7 in the link. I think it's saying that there is a chimney at the top of the building, which is square-shaped in cross section. The points of the square are oriented along the cardinal directions (NESW). The SE and SW faces should be painted black to absorb heat from the sunlight which falls on them. The NE and NW faces will always be in shadow, so don't need to be black. I'm not sure why they need to be clear.

This would heat the air in the tube, lowering the pressure. Assuming the house is a mostly sealed vessel, then the greater pressure from the cooling shaft's opening will drive flow into the house, and push the heat out of the exhaust tube. This would initiate a flow.

Keeping the windows and doors closed and sealed would be hugely important to keep the inflow from being diverted away from the cooling shaft.

[OngBonga]

IDK about the 45 degree angle. It could just come in from the side, above the cool air moving out. Wind is going to alter the angle, at any rate. The atmosphere is fairly thin sheet in cross-section.

Yeah I mean I was very much simplifying the process, it should be more considered an average approach angle. I figure it must be drawn in from above the cold air that is moving away, but it's not coming from directly above because humid air is rising.

And even as I said "hot air rises", I knew that could be nitpicked. I even nearly reworded it to "hot air tends to rise" but it essentially means the same thing. I understand WHY hot air rises, rather than just blindly accepting it as some magical property of heat. It's gravity and density at work here. Hot air is buoyed by cold air, that's probably a more accurate way of saying it! It's not quite as slick a phrase though.

[OngBonga]

Ok so let me see if I understand why humid air is less dense than dry air...

Dry air is mostly made up of oxygen and nitrogen. Water is oxygen and hydrogen. Hydrogen is much lighter than nitrogen. Furthermore, the oxygen in the atmosphere is O2 (nitrogen is N2 also, I believe), but there is only one atom of oxygen in a water molecule. Thus, dry air is significantly heavier than humid air as it contains more oxygen, and nitrogen.

It just seems crazy to think that water is lighter than air on a molecular level. But it's also makes sense when you look at water's structure. Two tiny hydrogen atoms and one oxygen atom. That's ten electrons per molecule. That's less than both N2 and O2, before we consider CO2 and the other trace gasses.

[MadMojoMonkey]

Ok so let me see if I understand why humid air is less dense than dry air...

Dry air is mostly made up of oxygen and nitrogen. Water is oxygen and hydrogen. Hydrogen is much lighter than nitrogen. Furthermore, the oxygen in the atmosphere is O2 (nitrogen is N2 also, I believe), but there is only one atom of oxygen in a water molecule. Thus, dry air is significantly heavier than humid air as it contains more oxygen, and nitrogen.

It just seems crazy to think that water is lighter than air on a molecular level. But it's also makes sense when you look at water's structure. Two tiny hydrogen atoms and one oxygen atom. That's ten electrons per molecule. That's less than both N2 and O2, before we consider CO2 and the other trace gasses.

It's no good to count electrons for the mass. A proton has about the same mass as a neutron, and both are about 1,800 times as massive as an electron. Furthermore, counting electrons is equivalent to counting protons (for atoms, not ions), but ignores the neutrons.

***
The point that you left out is Avogadro's Law. Avogadro hypothesized that equal volumes of gas will contain equal number of particles if they are at the same temperature and pressure.

Essentially, this says that the volume any gaseous molecule "occupies" is the same, regardless of its atomic constituents. It doesn't mean that the molecules are the same volume. A lighter particle with the same kinetic energy as a heavier particle will move more quickly. It covers more distance between particle collisions, and occupies a greater volume as such.

***
Using Avogadro's Law and further simplifying out the mass of the electrons and assuming all generations of atom are of the most common isotope, and that E=mc2 isn't acting to increase the mass of the nucleus due to bonding energy:
(All of these are small effects, compared to the result we will get.)

The air is mostly N2 and O2, which have equal numbers of neutrons as protons in their nuclei. This fact is not obvious, and has been obtained by observation. It was later shown via QM that this is a predictable result.

Nitrogen atoms have 7 protons and 7 neutrons, giving an atomic mass of 14. The molecule N2 has atomic mas of 28.
Oxygen atoms have 8 protons and 8 neutrons, giving an atomic mass of 16. The molecule O2 has atomic mas of 32.

Hydrogen atoms have 1 proton and 0 neutrons, giving an atomic mass of 1.
Water atoms have 1 Oxygen and 2 Hydrogens, giving an atomic mass of ( 16 + 1 + 1 = ) 18.

***
Taking the assumption that all 3 molecules occupy the same volume, water is the least dense.

EDIT: water atoms? lol. water molecules, obv.

[Eric]

What are the cliff notes on the way quantum physicists answered Einstein's questions below?

He [Einstein] imagined two boxes, one of which we know contains a ball.
...
Einstein wrote [to Schrodinger]: I describe a set of affairs as follows: the probability is 1/2 that the ball is in the first box. Is that a complete description? No: A complete statement is: the ball is (or is not) in the first box. That is how the characterization of the state of affairs must appear in a complete description. Yes: Before I open them, the ball is by no means in one of the two boxes. Being in a definite box comes about only when I lift the covers.
[Einstein by Walter Isaacson page 455]

"When a mouse observes," Einstein asked them, "does that change the state of the universe?"[Einstein by Walter Isaacson page 515]

[MadMojoMonkey]

He [Einstein] imagined two boxes, one of which we know contains a ball.
...
Einstein wrote [to Schrodinger]: I describe a set of affairs as follows: the probability is 1/2 that the ball is in the first box. Is that a complete description? No: A complete statement is: the ball is (or is not) in the first box. That is how the characterization of the state of affairs must appear in a complete description. Yes: Before I open them, the ball is by no means in one of the two boxes. Being in a definite box comes about only when I lift the covers.
[Einstein by Walter Isaacson page 455]

This one's tough. It seems he answered the question with both a no and a yes, proposing a rigid dichotomy. QM denies this rigid interpretation and any single, intuitive result.


The classical answer is no. The ball is either in the first box or it isn't. No method of observation is going to alter that. The timing of the observation will not change this. The ball is where it is, and though this information is hidden, it is unchanging.


The QM answer is: It depends on the nature of the system.
If your "ball" is a macroscopic object, composed of a 'large' number of particles, then it will act as the statistical average of all the uncertainties of all the particles, which means it will act classically.

If your ball is a particle, then it still depends. The particle could have any probability of being in the first box at any given time, depending on the setup of the situation. The probability could be 1/2 and steady, or it could be oscillating between 2 values. The only thing that is demanded is that at any given time, the total probability for the particle existing somewhere is 100%, and at no point is the probability less than 0%.

The particle may even have a probability of being found outside of either box. This is because particles tunnel through boundaries, even as they are "bouncing" off of them. Meaning that the particle has a nonzero probability of being found in neither box.

"When a mouse observes," Einstein asked them, "does that change the state of the universe?"[Einstein by Walter Isaacson page 515]

"Yes," they said.

It is impossible to acquire information without interaction. If that interaction yields no change, then we can rightly question whether there was an interaction at all.

If we have stipulated an observation, then we have stipulated a change.

[MadMojoMonkey]

Here's an excellent video from Crash Course on the topic of photons and atoms.



I love that he showed the stairwell, and went to one with different sized steps.

[Eric]

"Yes," they said.

It is impossible to acquire information without interaction. If that interaction yields no change, then we can rightly question whether there was an interaction at all.

If we have stipulated an observation, then we have stipulated a change.

Can one observe/acquire info without light being involved?

[MadMojoMonkey]

Can one observe/acquire info without light being involved?

I have to interpret "one" as "any instrument". Allowing a human observer adds an electro-chemical soup of an observer which certainly can't function w/o light involved.

One example is that an electron can be accelerated by absorbing a neutrino, and the exchange particle is a Z boson, and not a photon.
The electron observes a force which is not mediated by a photon.

Other examples are equally esoteric on a brief search.

It's because light is the force carrier for electromagnetic interactions. Atoms are made of charged particles. If charged particles are doing stuff, then electromagnetic fields are involved, which means photons.

Gluons mediate forces within atomic nuclei, but it's the same problem with the quarks being charged particles, so photons are involved, too.

Gravitons are hypothetical. If observed, they would fit the bill. They would be massless, which means they would move at the speed of light and have infinite range... like photons in so many ways, really.


Which leaves the W and Z bosons and the weak nuclear interactions.

***
So the answer is that particles can interact via particles which are not photons. However, atoms are made of charged particles which kind of necessarily involves photons.

[OngBonga]

Well that was certainly a fascinating discussion about atmospheric dynamics. I think I'm exhausted on that one, not sure I can add anything more. I'd like to have a better understanding of these kind of things, this is why I want to study environmental science.

Also, natural science...

Last night I was ranting with friends on facebook after I updated my status to...

Good. It's raining. I hope all the moths are drowning.

This sparked a discussion about the "intelligence" of moths, and their method of navigation. I know this isn't physics, but I wondered if you had any thoughts. I mean I'm just doing my talking shit thing here where I'm not actually fact checking anything, instead just basically rehashing stuff I've read or saw in a documentary maybe years ago.

The moon thing is kind of an urban myth. They're not actually trying to fly to the moon, they just use the moon to navigate. All they are trying to do is fly in a straight line. The moon would help them do this, because it remains fixed in its positon as you travel. If the moon remains at 3 o'clock, it's flying in a straight line. To a stupid moth with very poor eyesight, they confuse lights with the moon. Lights don't remain fixed in the sky, because they're not hundreds of thousands of miles away. They're meters away. It doesn't take long to pass it, unlike the moon, which would take centuries at moth pace. But instead of thinking "holy shit I'm going fast if that's the moon", they adjust their flight to "fix" the position of the "moon". "There, it's back at 3 o'clock, it must be the moon after all". So all the time the stupid twats are spiralling into fire and death, they think they're flying in a straight line towards bitches for a fuckfest. Do they serve a purpose? I think bats eat them. I guess that's a good thing. Bats are cool.

Would you say this is an accurate interpretation of moth navigation?

Also, I think the spider that is sitting upside down on my ceiling is dead. It hasn't moved for a day. How is it still attached to the ceiling if it's dead?

[a500lbgorilla]

Sounds about right. It reminds me of a story about a beehive where scientists placed food directly above the hive. Usually when a bee finds food, he goes back to the hive and does a figure 8 where he wiggles through the center pointing in the direction of the food. The bee accomplishes this by using the sun to navigate. The sun's ultraviolet rays penetrate the hive and it's visible to the bees inside. Well, when the food was straight up from the hive, the bee had no way of communicating this to the other bees, so it just danced around haphazardly.

[MadMojoMonkey]

The sun's ultraviolet rays penetrate the hive and it's visible to the bees inside.

srsly?

Cool.

Bee navigation is much studied.

A fairly simple source

An (undergrad?) paper on bee navigation

If you google "bee navigation" you can find articles at whatever scholarly level you're willing to read, apparently.

[a500lbgorilla]

I guess it's UV vision plus an ability to ballpark the sun's position based on an internal clock.

[MadMojoMonkey]

I guess it's UV vision plus an ability to ballpark the sun's position based on an internal clock.

This said nothing about the statement that the hive is transparent to UV light.

Do you have a source on that? My preliminary search turned up that bees like dark hives, and will cover over any lights with propolis to get rid of the light.

[OngBonga]

I liked to think bees at least had enough about them to have a "fuck this, just follow me" level of intelligence.

[a500lbgorilla]

How does a bee tell another bee, "fuck this, just follow me."?

[OngBonga]

By stopping its haphazard dance and flying in the direction of the food? I'd follow it if I were a hungry bee who didn't know what he was trying to say. Then again I'm pretending to be a hungry bee with the brain of a stoned adult human.

[MadMojoMonkey]

When it comes to animal intelligence, I think it's far too easy to anthropomorphize creatures which we have no solid reason to. I don't know what my cat, a fellow mammal, is thinking, let alone what an insect is thinking.

***
Moths and flames:
Almost all the reference material says that bit about moonlight is what's going on and talks about transverse orientation to celestial bodies as a common guidance method for migratory animals.

This article, interestingly, debunks a lot of hypotheses
TL;DR
A) Navigation by moonlight or starlight is almost unheard of in non-migratory animals. Over 50% of moth species are non-migratory.
New research suggests (at least some) migratory birds can sense the Earth's magnetic field, and do not navigate by moonlight.
B) Artificial light sources have been around for over 400,000 years in the form of campfires. The hypothesis that moths have failed to adequately evolve to understand and deal with modern light sources is thin.*
C) There was a hypothesis that female moth's hormones emit light, and that male moths were confusing fire light for steamy females. However, the emission spectrum of a campfire is very different from the spectrum of female moth hormones.

*However, 400,000 years isn't really that long on an evolutionary scale and if the young and virile moths aren't killing themselves, then it wont be selectively bred out of the species. Natural selection is only concerned with survival of the most fit reproducers. Any disease or affliction that affects a being after it has produced offspring is that being's own problem.

In conclusion: We don't know what's up with moths and their kamikaze behavior.

[OngBonga]

*However, 400,000 years isn't really that long on an evolutionary scale and if the young and virile moths aren't killing themselves, then it wont be selectively bred out of the species. Natural selection is only concerned with survival of the most fit reproducers. Any disease or affliction that affects a being after it has produced offspring is that being's own problem.

Yeah I think this is what I'd argue, I mean it's not like it's a high percentage that spiral into fire. I would imagine those at the most risk are those that have the "moon" positioned at a small angle relative to flight, ie directly in front of them. This would reduce their adjustments, compared to a moth who views the "moon" at 90 degrees.

I did have a quick look at the wiki page for moths, and there's only a couple of species that have evolved methods of defence against bats. There's one which instinctively drops a few inches when it detects sonar, and there's another that emits clicks to throw the bats off the scent. They're taking their time to evolve against predators, so it doesn't surprise me that fire isn't an evolutionary concern for them either. Maybe the ones who survive are the smarter ones who realise it's not the moon when they see how fast the angle is changing. Maybe in time the moths will stop dive bombing fire. I hope not, it amuses me.

[a500lbgorilla]

Yeah, I misremembered. It's UV light outside, internal clock inside.

[MadMojoMonkey]

WoooHooo!

NASA's New Horizons Probe reports all systems nominal after the flyby on Pluto!

WoooHoooo!

[OngBonga]

If electricity always follows the path of least resistance, why doesn't lightning only strike France?

[wufwugy]

Not a physics question but I'll ask here. Is there any real world application to mathematical proofs?

[MadMojoMonkey]

Every proof just shows a shortcut to get an answer more quickly. The need for the shortcut in a real world situation is often a motivation to prove something. Equally, though, many proofs are purely motivated by mathematical curiosity.

The proof is to show that the shortcut follows from the axioms without breaking a logical progression.

E.g. If you have a data set generated by a random variable and you want to describe it... you ultimately want to know that the way you think you're describing it is actually how you're describing it.

Suppose you want to know the EV of the next value to be collected to the data. Should you use the mean? The median? The mode?

We use a formal language to say, we want the unbiased estimator of the data set's EV. This is a complicated proof, but ultimately it shows that the mean is the one we want. So, knowing that, we don't need to go through the whole derivation of what formula gives us the EV, we can just use the mean and know that we're justified.

The same is true for the variance and standard deviation, and plenty of other stats. So we now have a small amount of data (these stats) which allow us to describe large amounts of data (the actual random variable). These are the shortcuts, and we know that we are justified to use them because we proved it.

Proving it once is enough. Just make sure that the axioms of your proof are in line with the axioms of your usage. If your usage doesn't match the assumptions of your proof, then you've got a bad model.

[a500lbgorilla]

Proofs from probability and statistics. They certainly have an application in games of chance where probabilities can be discretely known, if you consider those part of the real world. It's interesting to think about what happens between a structured double-blind study of some drugs effectiveness over to that drug's impact on the wider population, do the probabilities transfer 1:1, because if they do, then that'd be the winner right there.

[a500lbgorilla]

That's if you consider the result of the proof having a real world application counting as the proof having a real world application.