Astrophysics and Cosmology - Discuss the Universe here

[Quick Karl]

Hey Karl, good to hear from you.

AO, what an awesome thread! I wonder if I could pose a question from a purely novice perspective?

Suppose we had a box that was a perfect mirror on the inside, as well as a perfect vacuum, and we shot 1 photon of visible light through a 1-photon diameter hole in the side of the box that opened and closed only at the instant the photon passed through and did not diminish the perfect vacuum or mirrored surface.

Would the photon bounce around in there forever? Would it always emit the same quantity of visible light or slowly diminish or change color over time? If diminished over time, what would happen to the energy the photon lost? Would the inside of the box be lit, or would it look like a firefly bouncing around - a point of light bouncing around?

May be a lil crazy but, that is one of those questions I have always wondered about?

[area51drone]

Karl, I have wondered that many many times myself... 

[Quick Karl]

Karl, I have wondered that many many times myself...

[West of the Rockies]

Hello, QK... We know each other well through the dreadful politics threads....  Can we separate ourselves from "the body politic" to address your question? 

I know very damn little about science -- it's been a long-ass time since high school chemistry and physics.  But I recall a law that said something like "Matter cannot be created or destroyed except in a nuclear reaction"...  If so, we must ask whether light is indeed particle or energy.  If it's particle, then I would guess the imagined photon you mentioned would bounce around ad infinitum, yes?  If light is, indeed, energy, well, then I have absolutely no answer whatsoever.

And that is my brilliant comment for this thread.

[Agent : Orange]

AO, what an awesome thread! I wonder if I could pose a question from a purely novice perspective?

Suppose we had a box that was a perfect mirror on the inside, as well as a perfect vacuum, and we shot 1 photon of visible light through a 1-photon diameter hole in the side of the box that opened and closed only at the instant the photon passed through and did not diminish the perfect vacuum or mirrored surface.

Would the photon bounce around in there forever? Would it always emit the same quantity of visible light or slowly diminish or change color over time? If diminished over time, what would happen to the energy the photon lost? Would the inside of the box be lit, or would it look like a firefly bouncing around - a point of light bouncing around?

May be a lil crazy but, that is one of those questions I have always wondered about?

Really interesting question, actually.

For simplicity, let's agree to say the experiment takes place in deep space, away from any significant gravitational influences. Just to restate the set up a bit, let's say that a cube has been built in which the interior surfaces are entirely covered with mirrors, including a small trapdoor that can open by some type of remote control and accurately enough to allow in exactly one photon. Let's suppose that the presence of the trapdoor doesn't influence the efficiency of the mirror at all and does not compromise the properties of the box interior. We will ignore the delivery procedure of the photon, let's say we are far away enough from the cube that our measuring and experimental apparatus does not affect the box in any way. When the trap door is opened, a single photon is shot through it by us at a great distance. Immediately after entering the door is closed. My goal in setting it up this way is to make sure that the box is isolated and free from any outside influence.

But the really significant question here is what do you mean by "perfect mirror"?

If the inside of the box is made out of real mirrors, then there is some absorption we need to take into account. In other words, no mirror is exactly perfect, no matter how ground, polished, etc. So in the real world there has to be some loss due to absorption. So when this happens the energy of the photon is absorbed by the mirror, and the temperature of the mirror will be raised by a miniscule amount (a temperature increase corresponding to the energy of one photon). The mirrors are made out of atoms after all, and one photon strike can transfer all of it's energy to an atom, raising the temperature of the material. So after some time there would not be anything in the box, but the box would be slightly warmer and even for a billion photons that temperature change will be nearly imperceptible but it should still occur. So another assumption is to say that we can measure very fine changes in temperature in order to see the heating of the box.

If the above paragraph does not apply and you want to use "100% efficient theoretical thought mirrors" to do the experiment which can not absorb energy and are not made of atoms (!) then yes, the photon will bounce around forever.

Another small point for you is that we only know what's going on inside the box by checking the temperature of the mirrors that make up it's interior. This means we never look inside the box, so we can't ever "see" what the photons would look like - we can only make an image using our eyes if photons can leave the box and strike our retina. In fact in vacuum there is no way to see the photons at all unless they reach your eye. So the idea of small fireflies doesn't really describe the situation. Unless you put an observing instrument inside the box you won't be able to see anything or access the interior at all while the experiment is going on.

There are other possibilities for such an experiment too. We've assumed "thick" walls/mirrors (ie large compared to the wavelength of the photon). For example if the walls are thin (ie, small with respect to the photon wavelength) then it should be possible for the photon to tunnel out of the box as well due to the quantum tunnelling phenomenon. But this is going a bit far a field of your original scenario

[Quick Karl]

Really interesting question, actually.

For simplicity, let's agree to say the experiment takes place in deep space, away from any significant gravitational influences. Just to restate the set up a bit, let's say that a cube has been built in which the interior surfaces are entirely covered with mirrors, including a small trapdoor that can open by some type of remote control and accurately enough to allow in exactly one photon. Let's suppose that the presence of the trapdoor doesn't influence the efficiency of the mirror at all and does not compromise the properties of the box interior. We will ignore the delivery procedure of the photon, let's say we are far away enough from the cube that our measuring and experimental apparatus does not affect the box in any way. When the trap door is opened, a single photon is shot through it by us at a great distance. Immediately after entering the door is closed. My goal in setting it up this way is to make sure that the box is isolated and free from any outside influence.

But the really significant question here is what do you mean by "perfect mirror"?

If the inside of the box is made out of real mirrors, then there is some absorption we need to take into account. In other words, no mirror is exactly perfect, no matter how ground, polished, etc. So in the real world there has to be some loss due to absorption. So when this happens the energy of the photon is absorbed by the mirror, and the temperature of the mirror will be raised by a miniscule amount (a temperature increase corresponding to the energy of one photon). The mirrors are made out of atoms after all, and one photon strike can transfer all of it's energy to an atom, raising the temperature of the material. So after some time there would not be anything in the box, but the box would be slightly warmer and even for a billion photons that temperature change will be nearly imperceptible but it should still occur. So another assumption is to say that we can measure very fine changes in temperature in order to see the heating of the box.

If the above paragraph does not apply and you want to use "100% efficient theoretical thought mirrors" to do the experiment which can not absorb energy and are not made of atoms (!) then yes, the photon will bounce around forever.

Another small point for you is that we only know what's going on inside the box by checking the temperature of the mirrors that make up it's interior. This means we never look inside the box, so we can't ever "see" what the photons would look like - we can only make an image using our eyes if photons can leave the box and strike our retina. In fact in vacuum there is no way to see the photons at all unless they reach your eye. So the idea of small fireflies doesn't really describe the situation. Unless you put an observing instrument inside the box you won't be able to see anything or access the interior at all while the experiment is going on.

There are other possibilities for such an experiment too. We've assumed "thick" walls/mirrors (ie large compared to the wavelength of the photon). For example if the walls are thin (ie, small with respect to the photon wavelength) then it should be possible for the photon to tunnel out of the box as well due to the quantum tunnelling phenomenon. But this is going a bit far a field of your original scenario

WOW!

Now THAT is the way to answer the question! I am completely awed, sir! "100% efficient theoretical thought mirrors" - I like that.

I am curious, what do you do that gives you this kind of insight?

[Quick Karl]

Next question, if you don't mind,

I have heard it said that the relative distance between the nucleus and electrons in an atom can be compared to the distance between the planetoid, Pluto, and the Sun. Regardless of the actual distances, let's agree that the distance is comparatively great, and that 90%, or thereabouts, of a molecule, is in fact, empty space - i.e. nothing.

Does that mean that everything we can see, feel, taste, and smell, is 90% nothing?

[aldousburbank]

Next question,

I have heard it said that the relative distance between the nucleus and electrons in an atom can be compared to the distance between the planetoid, Pluto, and the Sun. Regardless of the actual distances, let's agree that the distance is comparatively great, and that 90%, or thereabouts, of a molecule, is in fact, empty space - i.e. nothing.

Does that mean that everything we can see, feel, taste, and smell, is 90% nothing?

No, it means that 100% of everything we can see, feel, taste, and smell is not everything.

[Quick Karl]

No, it means that 100% of everything we can see, feel, taste, and smell is not everything.

Aldous, sir,

I have told you previously, you are a genius in your own right!

[Quick Karl]

This is what an Internet Discussion forum should be.

[aldousburbank]

Aldous, sir,

I have told you previously, you are a genius in your own right!

Mostly left, but I try to balance by readjusting stuff regularly.

[area51drone]

Really interesting question, actually.

For simplicity, let's agree to say the experiment ...

The answer makes complete sense.  I had always thought of it as letting a lot of light (billions of photons as you said) into the internally mirrored box, not just one photon, but wondered if you just captured a little ball of light that could then be unleashed at some point.   Clearly, you're right Agent, the answer is no.   And it makes perfect sense that mirrors cannot be perfect and will have some loss.   So let's take this to the next logical step - assume the mirror is in empty space - the photon heats up the mirror, and that heat transfers up into and out of the back of the mirror, and dissipates out into space, becoming just another blip in the cosmic background radiation?   Can that heat be converted back into something, somewhere, and do something useful or is it forever just going to dissipate further as space expands?

I also have another question for you Agent, or anyone who wants to take a shot - why is it that space is expanding only in certain places in the universe, and in others - such as the earth, or even your own body, space stays the same?    Has anyone been able to map where the expansion of the universe occurs?

[area51drone]

Hey, it's cold and clear outside tonight.   If I can get my work done fast enough, I'm going to see if the CCD will fit in my scope tonight.   Wish me luck!   I'm thinking it if works, it would be really cool to setup a live BellGab viewing party where I stream the cam if possible and you guys direct me to slew to different objects in the sky.  Maybe something we could do once a month or every other month or something.

[aldousburbank]

I also have another question for you Agent, or anyone who wants to take a shot - why is it that space is expanding only in certain places in the universe, and in others - such as the earth, or even your own body, space stays the same?    Has anyone been able to map where the expansion of the universe occurs?

In the area directly surrounding Tommy's butt?

[Quick Karl]

M31 is an awesome sight!

Have you ever heard of a computer program named Stellarium? http://stellarium.org/

It is free!

[aldousburbank]

Hey, it's cold and clear outside tonight.   If I can get my work done fast enough, I'm going to see if the CCD will fit in my scope tonight.   Wish me luck!   I'm thinking it if works, it would be really cool to setup a live BellGab viewing party where I stream the cam if possible and you guys direct me to slew to different objects in the sky.  Maybe something we could do once a month or every other month or something.

I think that is an excellent concept 51.  I dunno, maybe some skype thang?

[area51drone]

M31

Have you ever heard of a computer program named Stellarium? http://stellarium.org/

It is free!

Yes, but I use Starry Night.

[steelbot]

Yes, but I use Starry Night.

great idea - I too, am really big into astronomy - and hope to have a homemade 10-12 inch scope some day, and will do this as well.  As for streaming it - hell just do a JustinTV stream if ya can - the Microsoft Lifecam HD guessing its 3xxx series - but it's barrel shaped to be fit on optics systems and are supposed to be pretty good.  I know my sister's boyfriend got this awesome binocular set with tripod and shit, and they provided a way better viewing of saturn, titan and the rings and all the other sky watchers delights than the 6 inch mead he has owned for years.

[Camazotz Automat]

I also have another question for you Agent, or anyone who wants to take a shot - why is it that space is expanding only in certain places in the universe, and in others - such as the earth, or even your own body, space stays the same?   

If the strong interaction, weak interaction, and electromagnetic force were compromised, we'd expand into great Macy's Thanksgiving Day parade floats/blobs.

Thought experiments are good for the graviton soul.

Yes, but I use Starry Night.

User Warning: During Starry Night program set up, you will be required to remove parts of your left ear.

Do you agree to these terms?

Select YES or NO.

[area51drone]

If the strong interaction, weak interaction, and electromagnetic force were compromised, we'd expand into great Macy's Thanksgiving Day parade floats/blobs.

Thought experiments are good for the graviton soul.

And yet, the graviton has yet to be discovered...   yet all these physicists act as if it must exist.   Curious to think what others think of this "toy model" paper... http://arxiv.org/abs/1211.4692   Dark matter be damned!

[area51drone]

User Warning: During Starry Night program set up, you will be required to remove parts of your left ear.

Do you agree to these terms?

Press YES or NO.

I had to cut off both ears fully.  I won't tell you why.

[area51drone]

the Microsoft Lifecam HD guessing its 3xxx series - but it's barrel shaped to be fit on optics systems and are supposed to be pretty good.

It's an AmScope 3 megapixel.

http://www.amazon.com/AmScope-Microscope-Digital-Software-Compatible/dp/B004WAGOKY/ref=sr_1_1?s=industrial&ie=UTF8&qid=1387868796&sr=1-1&keywords=amscope+3mp

I bought this one specifically because reviews said it handled low light better than some of the higher MP ones, plus the higher MP ones are a lot more expensive.  I figured the low light sensitivity might make it okay for a telescope.  It is also a CMOS sensor, which other telescope cameras are as well, so as long as I can mount it, I think it should work, and I'll be glad to have a camera that is useful for showing my kids things very big and things very small.

[Camazotz Automat]

I think that is an excellent concept 51.  I dunno, maybe some skype thang?

(Next ZZ Top song : Skype Thang )

[Agent : Orange]

And yet, the graviton has yet to be discovered...   yet all these physicists act as if it must exist.   Curious to think what others think of this "toy model" paper... http://arxiv.org/abs/1211.4692   Dark matter be damned!

This model explains dark matter by a massive graviton. They also introduce a new universal constant acceleration, the origin of which is mysterious. So you could argue that they've traded one mystery for another. Still it's an interesting paper, though there are some big challenges ahead, they have to explain complicated lensing results above and beyond individual galaxies interacting, like the bullet cluster and other such large systems. There are no comments in this paper on the cosmological implications for the theory, and the crucial test, how well it fits the power spectrum of the CMB. If they can have a go at all of this stuff then it becomes more interesting.

[area51drone]

Hey, to be fair, they do say it is a toy model.  I just thought it was interesting, that's all.

[Agent : Orange]

The answer makes complete sense.  I had always thought of it as letting a lot of light (billions of photons as you said) into the internally mirrored box, not just one photon, but wondered if you just captured a little ball of light that could then be unleashed at some point.   Clearly, you're right Agent, the answer is no.   And it makes perfect sense that mirrors cannot be perfect and will have some loss.   So let's take this to the next logical step - assume the mirror is in empty space - the photon heats up the mirror, and that heat transfers up into and out of the back of the mirror, and dissipates out into space, becoming just another blip in the cosmic background radiation?   Can that heat be converted back into something, somewhere, and do something useful or is it forever just going to dissipate further as space expands?

That one photon of thermal radiation will be set loose in the universe like a drop of water in the ocean. What happens to it after our experimental apparatus radiates it away is another story.

I also have another question for you Agent, or anyone who wants to take a shot - why is it that space is expanding only in certain places in the universe, and in others - such as the earth, or even your own body, space stays the same?    Has anyone been able to map where the expansion of the universe occurs?

The expansion happens at all points in the universe equally, but it's only observable on very large scales, so in structures that are small the gravitational, electromagnetic and other forces completely overwhelm the expansion. So small bound systems can stay bound even though the space-time they're in is expanding.  The units we measure the acceleration in are km/s/Mpc which means you get 1 km/s of velocity from every megaparsec of distance. The prefix mega means a million, and a parsec is 3.26 light years. This unit tells you that two points in space time separated by 3.26 million ly will expand at a rate of 1 km/s due to the expansion of the universe. So for reasonable values of the Hubble constant and the cosmological constant it's a reasonably small velocity and is completely overwhelmed for distances much smaller than parsec scales. There are papers that have calculated the effects of cosmological constant on the formation of black holes and neutron stars but the acceleration would have to be so ridiculously huge to affect the formation of these things at all that in our universe the effect of expansion is completely negligible for such systems.

Again, very interesting, there are a set of cosmologies which could have some support for them from the planck data, depending on the state of the 217 GHz data mentioned earlier, that might have the cosmological constant not constant at all, and increasing in time. In this case the accelerated expansion is described by a type of field called a scalar field. The end state for such a universe with scalar field driven expansion could then be a "big rip" if the expansion constantly increases in magnitude. This means at some future point the accelerated expansion would become so severe to rip apart all bound structures, including galaxy clusters, galaxies and even atoms themselves. 

[Agent : Orange]

Hey, to be fair, they do say it is a toy model.  I just thought it was interesting, that's all.

Absolutely!

[area51drone]

Okay, I need to get to bed so I just quickly set the telescope up and snapped this pic with the default optics.   I didn't bother looking for stars, it's late and I don't have time right now, plus clouds were starting to roll in.   Click for bigger picture.

[Agent : Orange]

Okay, I need to get to bed so I just quickly set the telescope up and snapped this pic with the default optics.   I didn't bother looking for stars, it's late and I don't have time right now, plus clouds were starting to roll in.   Click for bigger picture.

Hey nice! You get some great relief on the craters near the terminator.

[Mind Flayer Monk]

Okay, I need to get to bed so I just quickly set the telescope up and snapped this pic with the default optics.   I didn't bother looking for stars, it's late and I don't have time right now, plus clouds were starting to roll in.   Click for bigger picture.

The picture was taken from holding your webcam to a telescope lens or just a normal digital camera held to a telescope lens?
It looks very nice.