Inside a Spherical Mirror

Dorfl · 2nd June 2009, 06:23 AM

If an astronaut, equipped with a flashlight, was floating inside a sphere with a perfectly reflective surface, what would he see?

Is there any software which could render his view approximately, or can it be figured out just with pen and paper?

Horatius · 2nd June 2009, 06:24 AM

Reading Spider Robinson?

Dorfl · 2nd June 2009, 06:29 AM

Originally Posted by Horatius

Reading Spider Robinson?

Yup. I became curious about what the answer actually was, and this seems like the likeliest place to find someone who knows.

Just thinking · 2nd June 2009, 07:14 AM

Sounds like everything would be reflected everywhere ... including the light from the flashlight.

Beerina · 2nd June 2009, 07:46 AM

As his body (and the flashlight) were the only things that absorbed the light, he would slowly heat up until he died. Assuming he didn't run out of oxygen first.

Visually, he would see the room get brighter almost instantly, and probably too bright to keep his eyes open. Whether it would be so bright he'd have to close his blast shield because his eyelids and, say, sun goggles weren't enough, who knows.

Beerina · 2nd June 2009, 07:49 AM

His best bet would be to move away from the exact center. In this way, some of the light would miss him and keep bouncing back and forth indefinitely.

Just thinking · 2nd June 2009, 07:52 AM

Originally Posted by Beerina

As his body (and the flashlight) were the only things that absorbed the light, he would slowly heat up until he died. Assuming he didn't run out of oxygen first.

Visually, he would see the room get brighter almost instantly, and probably too bright to keep his eyes open. Whether it would be so bright he'd have to close his blast shield because his eyelids and, say, sun goggles weren't enough, who knows.

You don't think his body could absorb the light from his flashlight quickly enough to reach some sort of equilibrium? It's likely only a single bulb of light measured in a few watts. Of course, he could always turn it off at any time. I suspect things would go completely dark very quickly should he do that. Also, we don't know how big the sphere is ... could have a radius the size of the orbit of Mercury.

JoeTheJuggler · 2nd June 2009, 07:58 AM

Originally Posted by Beerina

His best bet would be to move away from the exact center. In this way, some of the light would miss him and keep bouncing back and forth indefinitely.

Depending on the size of the sphere relative to the size of the guy, he could also lie against the surface of the sphere and block some portion of it from reflecting the light.

Unlike a Bull · 2nd June 2009, 09:09 AM

I think there are a lot of variables that would effect what he saw. If the sphere is huge, the light would probably be so diffused that he might see a faint glow in some directions and probably blackness in others. If the sphere was pretty small (and we assume a regular flashlight, not a giant spotlight or anything) I think he would see kind of a blurry reflection of himself in some directions and a reflection of bright light (not any brighter than the bulb) in others. I think he would absorb enough of the light so that it wouldn't really be blinding, unless he lined up the flashlight so that it reflected right into his eye after only a couple reflections without being blocked by his body at all. Mirrors aren't perfectly reflective, so with each reflection some of the light would be lost (actually converted to heat).

Now if we consider a "point astronaut"

then (I think) more of the energy coming from the flashlight would preserved as light instead of converting to heat in which case it might get to a blinding level ... if point astronauts have eyes

.

I don't think the thing would heat up enough to kill the astronaut. Eventually the sphere is going to reach an equilibrium where it's emitting the same amount of energy as is coming out of the flashlight, it's just a matter of how hot it get's before that equilibrium is reached. This is dependent on how much energy is coming out of the flashlight and how well the sphere can release heat. Fortunately for the astronaut, I don't think the flashlight would really be strong enough to kill him. However, if we make the sphere sufficiently insulated ... well, it would be curtains for the astronaut. Of course the astronaut would be creating his own heat as well. Hmm, there must be some point of insulation at which if the astronaut doesn't turn on his flashlight, he won't reach a temperature to kill him, but if he does use his flashlight, he'll overheat though I'm sure it's a very fine line.

Going back to the "point astronaut", when the inside of the sphere reached a point where there was enough light hitting the mirrored surface so that it's reflective inefficiency caused the sphere to lose enough heat to it's surroundings to reach equilibrium, it would no longer get any brighter inside. Adding an astronaut with physical size just gives the system another way to convert light to heat. And (I think), since there would be heat energy inside the sphere that could heat up the sphere shell, helping it to release heat, less light would have to strike it to be converted to heat to reach equilibrium.

So, the smaller the astronaut the brighter the inside of the thing would be.

Also, there are many people on this forum that have much better understanding of physics than I do. So please, if anything I have said isn't accurate, don't have any reservations about letting me know.

edit: Missed the part about it being perfectly reflective. In which case, the mirror would not convert the light to heat. The point astronaut would result in the inside of the sphere becoming increasingly more bright until the flashlight stopped emitting light. The astronaut with physical size would be the sole converter of light to heat (assuming the inside of the sphere is a vacuum, which I think we're supposed to assume because it's in space) and his best bet would be to get as much of himself as possible pressed against the surface of the sphere so that conduction can occur. And turning off the flashlight might not be such a bad idea.

Dorfl · 2nd June 2009, 10:22 AM

Originally Posted by Unlike a Bull

Now if we consider a "point astronaut"

then (I think) more of the energy coming from the flashlight would preserved as light instead of converting to heat in which case it might get to a blinding level ... if point astronauts have eyes

.

Now that I think about it, it isn't necessarily the case that both of the astronaut's eyes would have at all the same view, so maybe we should assume that he is point-shaped. But then again, if he lacked extension in space there would not be anything for him to see reflected inside the sphere. Maybe we should assume that he is one-eyed.

rwguinn · 2nd June 2009, 10:48 AM

I'm sorry--What?
There is limited energy available in the flashlight. There is no way that the mirrored sphere itself can increase that. So the max temperature increase (from the flashlight) is that which would occur if the batteries discharged instantaneously.
Light brightness is proportional to the inverse of the distance traveled. Depending on the size of the sphere, the n^th reflection is going to be too dim to see, and none of them are going to blind him any worse than the flashlight itself will if he looked directly into it (and the light that hits him is blocked/ diffused, and no longer as energetic.

He's in a hell of a lot more danger of overheating from his own metabolism

jasonpatterson · 2nd June 2009, 12:38 PM

Originally Posted by rwguinn

I'm sorry--What?
There is limited energy available in the flashlight. There is no way that the mirrored sphere itself can increase that. So the max temperature increase (from the flashlight) is that which would occur if the batteries discharged instantaneously.

Light brightness is proportional to the inverse of the distance traveled. Depending on the size of the sphere, the n^th reflection is going to be too dim to see, and none of them are going to blind him any worse than the flashlight itself will if he looked directly into it (and the light that hits him is blocked/ diffused, and no longer as energetic.

I agree entirely with the first part, the second part makes a false assumption. The danger to the person inside the mirror is non-existent, no more so than if you took a flashlight and shined it on a spot on your arm until the batteries died. You wouldn't overheat, you wouldn't catch fire, nothing would happen of particular importance.

The brightness of light falls as the square of the distance traveled for a spherical emitter, however, in this case, assuming a perfect mirror, it would disperse, but the light would not escape, instead it would be continuously reflected back until it was absorbed. In short, it is not a spherical emitter.

If the person inside the sphere was coated with perfect mirror except for the eyes, then it would brighten until the eyes were absorbing the full strength of the flashlight, close to what you would experience by putting a flashlight right in front of your eyes and turning it on. At that point the flashlight would be releasing light into the room at the same rate that the eyes were absorbing it and you'd have an equilibrium of sorts.

If the person's eyes were perfect mirrors themselves (or point objects with zero surface area, or perfectly transparent, for that matter) then the person would be completely blind since it takes some absorption of light for vision to occur. That was what always bothered me about the invisible man...

Dorfl · 2nd June 2009, 01:35 PM

If we assume that heating is not a problem, does anyone know what the astronaut's view would look like?

Intuitively, it feels to me like he would be seeing himself, smeared over the inside of the sphere. After all, a line drawn from his eye in any direction, reflecting off the walls, would intersect his body (or the flashlight) eventually. I might be wrong though, and it is not a very detailed picture anyway. Does anyone have a better idea?

rwguinn · 2nd June 2009, 03:02 PM

Originally Posted by jasonpatterson

I agree entirely with the first part, the second part makes a false assumption. The danger to the person inside the mirror is non-existent, no more so than if you took a flashlight and shined it on a spot on your arm until the batteries died. You wouldn't overheat, you wouldn't catch fire, nothing would happen of particular importance.

The brightness of light falls as the square of the distance traveled for a spherical emitter, however, in this case, assuming a perfect mirror, it would disperse, but the light would not escape, instead it would be continuously reflected back until it was absorbed. In short, it is not a spherical emitter.

If the person inside the sphere was coated with perfect mirror except for the eyes, then it would brighten until the eyes were absorbing the full strength of the flashlight, close to what you would experience by putting a flashlight right in front of your eyes and turning it on. At that point the flashlight would be releasing light into the room at the same rate that the eyes were absorbing it and you'd have an equilibrium of sorts.

If the person's eyes were perfect mirrors themselves (or point objects with zero surface area, or perfectly transparent, for that matter) then the person would be completely blind since it takes some absorption of light for vision to occur. That was what always bothered me about the invisible man...

I think we said the same thing.

mhaze · 2nd June 2009, 03:39 PM

Originally Posted by Beerina

As his body (and the flashlight) were the only things that absorbed the light, he would slowly heat up until he died. Assuming he didn't run out of oxygen first.

Visually, he would see the room get brighter almost instantly, and probably too bright to keep his eyes open. Whether it would be so bright he'd have to close his blast shield because his eyelids and, say, sun goggles weren't enough, who knows.

NO!

The flashlight has an "ON" and an "OFF" switch. Everyone knows that "OFF" switches DARK ON. Thus the flashlight operates both as a light emitter, and a lightsucker.

"OFF" mode is very efficient, allowing the flashlight to be used as a propulsion device by the astronaut in the sphere by simply pointing where he wants to go, clicking the switch, and vacuuming up photons, which creates the powerful pull forces required for intersteller travel inside a spherical mirrored device.

What is done with the vacuumed up photons? They are resold on the black market - regions of the universe high in dark matter.

Piscivore · 2nd June 2009, 03:45 PM

I want to see Mythbusters build this.

Unlike a Bull · 2nd June 2009, 04:59 PM

Originally Posted by mhaze

What is done with the vacuumed up photons? They are resold on the black market - regions of the universe high in dark matter.

I bought some of those photons once. They're not nearly as good as fresh photons. You should always buy your photons from a reputable source.

By the way, I've squandered some of my precious day off doing some math on this.

If we assume the flashlight uses two size D batteries and they each contain 75,000 joules of energy ( http://www.allaboutbatteries.com/Energy-tables.html we'll assume alkaline batteries although I'm sure NASA uses some crazy alien-technology, area 51 type battery. Probably Lithium-ion.) that would be some 150,000 joules together.

http://www.engineeringtoolbox.com/hu...eat-d_393.html says the average human body has a specific heat of 3470 J/kgC. So if we ignore his gear and flashlight, and assume he is 70 kilograms ... his temperature will go up by about .6 degrees C. Not enough to kill him. We need bigger batteries.

Floyt · 2nd June 2009, 06:38 PM

Originally Posted by Dorfl

If we assume that heating is not a problem, does anyone know what the astronaut's view would look like?

Intuitively, it feels to me like he would be seeing himself, smeared over the inside of the sphere. After all, a line drawn from his eye in any direction, reflecting off the walls, would intersect his body (or the flashlight) eventually. I might be wrong though, and it is not a very detailed picture anyway. Does anyone have a better idea?

As I understand it, he wouldn't be seeing anything but a glare from any direction - the flashlight is the only emitter of light, whereas his body etc. only reflect - this would be swamped by the continuous emission from the flashlight.

(Just tried to model that in a Bryce scene, with a light source and a stone texture cube inside a perfectly reflective sphere. Sure enough, once you enable total internal reflection to a high degree (obviously infinite is not available, but a couple hundred iterations can be done in acceptable time), it's all shapeless glare. I wouldn't treat that as any great evidence obviously, although Bryce's laws of optics are pretty good.)

technoextreme · 2nd June 2009, 06:50 PM

Isn't this just an integrating sphere?

Tricky · 2nd June 2009, 06:50 PM

He would receive no more energy than he would if he shone the light directly on himself. The sphere only reflects energy, it does not amplify it.

Seeing as the mirror is convex though, it would reflect back as a tiny point of light (which he would see in any direction he looked). Depending on the focal length of the sphere's convex side, though, he might be focusing the flashlight to a tiny point that could give him small local burns.

Note also that we only need to be concerned with the first reflection of the light. After it is reflected and the distance between the source and the observation point becomes so great that the light is greatly diffused and will just provide a dim glow.

Don't look at the first reflection directly though, although if my scenario is correct, the only way that could focus directly on the eyes is if he was holding the flashlight between his eyes.

Anyway, that's my take.

Tricky · 2nd June 2009, 06:57 PM

I don't know if any of you have been to The Bean in downtown Chicago. It is an amazing sculpture and very reflective both inside and out. As you can see from the outside picture, the bean has a little concavity that you can walk inside. The second picture is taken from the inside.

I have more if you are interested.

Stellafane · 2nd June 2009, 08:18 PM

Originally Posted by Tricky

He would receive no more energy than he would if he shone the light directly on himself. The sphere only reflects energy, it does not amplify it...

This is of course correct. I think some may be confusing the situation described in the OP with that of an astronomical telescope, which as is well-known can take a pinpoint of light in the sky (often so dim it's invisible to the naked eye) and make it dazzlingly bright. But the reason a telescope can do this is because there's a lot of starlight falling on every square inch of Earth, and the telescope grabs a sizable patch of it and concentrates it into a tiny point. The total amount of theoretically available starlight is quite high because the original source of the light is extremely large and bright, and even at stellar distances produces a considerable amount of illumination falling on the Earth. The flashlight, on the other hand, produces a very limited amount of light. So even if you get every photon of light bounced back to you, it can never be brighter than the original flashlight bulb -- visible, but certainly not a blinding sheet of illumination.

Dorfl · 3rd June 2009, 03:37 AM

Originally Posted by Floyt

As I understand it, he wouldn't be seeing anything but a glare from any direction - the flashlight is the only emitter of light, whereas his body etc. only reflect - this would be swamped by the continuous emission from the flashlight.

(Just tried to model that in a Bryce scene, with a light source and a stone texture cube inside a perfectly reflective sphere. Sure enough, once you enable total internal reflection to a high degree (obviously infinite is not available, but a couple hundred iterations can be done in acceptable time), it's all shapeless glare. I wouldn't treat that as any great evidence obviously, although Bryce's laws of optics are pretty good.)

Hm, I didn't think of that. Intuitively I assumed that looking in any direction, he would see either a light beam coming from his own body, or one from the flashlight. So at worst his view would be divided into bright fields from the flashlight, and dim ones from himself. But if you say Bruce gives a uniform glare, I suppose my picture must be wrong.

What if the astronaut himself were the light emitter? (Maybe Doctor Manhattan created himself a mirrory sphere, just to see what would happen.)

Cuddles · 3rd June 2009, 06:19 AM

Originally Posted by Unlike a Bull

If we assume the flashlight uses two size D batteries and they each contain 75,000 joules of energy ( http://www.allaboutbatteries.com/Energy-tables.html we'll assume alkaline batteries although I'm sure NASA uses some crazy alien-technology, area 51 type battery. Probably Lithium-ion.) that would be some 150,000 joules together.

http://www.engineeringtoolbox.com/hu...eat-d_393.html says the average human body has a specific heat of 3470 J/kgC. So if we ignore his gear and flashlight, and assume he is 70 kilograms ... his temperature will go up by about .6 degrees C. Not enough to kill him. We need bigger batteries.

I don't think that's correct. You're assuming that his body simply absorbs all the energy. However, at the same time it will be acting as a black body emitter. In fact, the astronaut is likely to be by far the biggest radiation source present. Assuming he has enough food, he'll eventually die once the inside of the sphere has heated up past 37^o and he can no longer regulate his body temperature.

dogjones · 3rd June 2009, 07:26 AM

Originally Posted by Unlike a Bull

I bought some of those photons once. They're not nearly as good as fresh photons. You should always buy your photons from a reputable source.

Maudsley does a good line.

Unlike a Bull · 3rd June 2009, 07:51 AM

Originally Posted by Cuddles

I don't think that's correct. You're assuming that his body simply absorbs all the energy. However, at the same time it will be acting as a black body emitter. In fact, the astronaut is likely to be by far the biggest radiation source present. Assuming he has enough food, he'll eventually die once the inside of the sphere has heated up past 37^o and he can no longer regulate his body temperature.

You are correct that I am incorrect

. I was just thinking about worst case (hypothetical) scenario where all the energy from the flashlight is converted to heat and all is transferred to his body. If this worst case scenario won't kill him then the lesser, realistic ones won't either.

I'm not sure if his metabolism would be enough to kill him either though. It is specified that the sphere reflects light perfectly, but nothing is said about it's heat conductivity. Therefore we're free to speculate! If the sphere is a perfect insulator, then yes his metabolism will eventually kill him. If, however, the sphere allows heat to be released to the surroundings then it's just a matter of how hot the thing will get before equilibrium is reached.

also, I don't think he would lose his ability to regulate temperature when the sphere reaches 37 C. I know he would lose his ability to radiate heat to his environment, but he could get creative. Once he started getting warm he would start sweating. He would be able to regulate temp through sweat for a while, but the air in his suit would become warm and humid pretty quickly. But, by venting this humid air into the sphere, he would be removing heat from himself and putting it into his environment. This air would then be replaced by whatever kind of breathing system he had. He would be able to do this for a while, since all he would need is a pressure difference to vent the air.

please note, I'm not saying that a 37 C astronaut could make his surroundings greater than 37 C, but by moving mass from himself to his surroundings, he can remove heat from himself.

Cuddles · 3rd June 2009, 07:57 AM

Originally Posted by Unlike a Bull

If, however, the sphere allows heat to be released to the surroundings then it's just a matter of how hot the thing will get before equilibrium is reached.

please note, I'm not saying that a 37 C astronaut could make his surroundings greater than 37 C, but by moving mass from himself to his surroundings, he can remove heat from himself.

Well, I assumed that since we were dealing with an astronaut that he'd be floating in a perfect vacuum. If you allow atmosphere inside then that changes things a bit, and by playing with the conditions inside and outside the sphere you can come up with pretty much any outcome you like.

Unlike a Bull · 3rd June 2009, 09:19 AM

Originally Posted by Cuddles

Well, I assumed that since we were dealing with an astronaut that he'd be floating in a perfect vacuum.

I'm operating under the same assumption (well, maybe not a PERFECT vacuum). I meant that the sphere would be able to radiate heat away from itself. When I talked about its conductivity I meant it's ability to transfer heat from it's inside edge to it's outside edge so that the energy could be radiated away, not that it would be conducting heat into some medium outside of it. Sorry if I wasn't clear enough.

Quote:

If you allow atmosphere inside then that changes things a bit

Why wouldn't you allow atmosphere in the sphere if it's vented from the astronauts suit?

Quote:

and by playing with the conditions inside and outside the sphere you can come up with pretty much any outcome you like.

Pretty much.

This is because we weren't given enough information in the OP, because the OP was about what the astronaut would see, not how hot he would get.

Cuddles · 3rd June 2009, 09:38 AM

Originally Posted by Unlike a Bull

I'm operating under the same assumption (well, maybe not a PERFECT vacuum). I meant that the sphere would be able to radiate heat away from itself. When I talked about its conductivity I meant it's ability to transfer heat from it's inside edge to it's outside edge so that the energy could be radiated away, not that it would be conducting heat into some medium outside of it. Sorry if I wasn't clear enough.

But if there's a vacuum inside the sphere then it can never absorb any heat. It's a perfect reflector, remember, so it can't absorb any radiation. An atmosphere would allow conduction, but if you get rid of that there's nothing.

Quote:

Why wouldn't you allow atmosphere in the sphere if it's vented from the astronauts suit?

Because, assuming the question was about what would happen in a vacuum, it would be changing the question. It's like starting with the question asking about a perfect reflector and then saying that the astronaut could throw something at it to break it. That sort of thinking is great for silly lateral thinking questions, but is utterly pointless when applied to thought experiments trying to answer a specific question.

For my part, I wouldn't allow atmosphere in the sphere if it's vented from the suit because I was thinking about what would happen in a vacuum. As I said, if you allow an atmosphere then you can come up with pretty much any result depending on what assumptions you make, but in that case it makes no difference where the atmosphere comes from, so it's completely pointless to wonder about different cooling systems the astronaut might have.

Unlike a Bull · 3rd June 2009, 10:33 AM

Originally Posted by Cuddles

But if there's a vacuum inside the sphere then it can never absorb any heat. It's a perfect reflector, remember, so it can't absorb any radiation. An atmosphere would allow conduction, but if you get rid of that there's nothing.

Oh! For some reason I was thinking perfectly reflective only in regards to visible light

. I see my error now. Thanks.

Dan O. · 4th June 2009, 06:52 AM

Originally Posted by Tricky

Don't look at the first reflection directly though, although if my scenario is correct, the only way that could focus directly on the eyes is if he was holding the flashlight between his eyes.

The first reflection will create a somewhat distorted and blurred image at a point that is an equal distance on the opposite side of the center of the sphere. The closer that the source is to the center, the sharper the image will be. If the astronaut is at the location of the first image, light would be seen coming from all directions except where the astronaut's own shadow blocked the light.

The intensity of the light at the image will follow the inverse square law with the distance measured from the image not the original source. The maximum intensity at the image cannot exceed the intensity of the source. However, since the image is not protected by a bulb, it is possible to get much closer to it.

If the astronaut is closer to the center than the source and on the line through the source and the sphere's center then the astronaut will not see the first image of the source except for some extra light coming from directly behind the source. The astronaut's own shadow will be blocking the light that would have created the image.

Anything inside the sphere that is illuminated (such as the astronaut) will be a secondary light source and will also produce an image opposite the center. The astronaut will see an image of himself but without the reversal that you see in a mirror. Also unlike an image produced by a flat mirror, it is possible to pass through this image by passing through the spheres center.

Dorfl · 4th June 2009, 11:36 AM

Originally Posted by Dan O.

The first reflection will create a somewhat distorted and blurred image at a point that is an equal distance on the opposite side of the center of the sphere. The closer that the source is to the center, the sharper the image will be. If the astronaut is at the location of the first image, light would be seen coming from all directions except where the astronaut's own shadow blocked the light.

The intensity of the light at the image will follow the inverse square law with the distance measured from the image not the original source. The maximum intensity at the image cannot exceed the intensity of the source. However, since the image is not protected by a bulb, it is possible to get much closer to it.

If the astronaut is closer to the center than the source and on the line through the source and the sphere's center then the astronaut will not see the first image of the source except for some extra light coming from directly behind the source. The astronaut's own shadow will be blocking the light that would have created the image.

Anything inside the sphere that is illuminated (such as the astronaut) will be a secondary light source and will also produce an image opposite the center. The astronaut will see an image of himself but without the reversal that you see in a mirror.

I have difficulty visualizing that, but it does sound cool.

Thank you very much, I had been wondering about it for a few years now.

Quote:

Also unlike an image produced by a flat mirror, it is possible to pass through this image by passing through the spheres center.

[Prince of Persia] Sheathe your sword and pass through your mirror image... It took me weeks to figure that out! [/Prince of Persia]

Timothy · 4th June 2009, 12:25 PM

Originally Posted by technoextreme

Isn't this just an integrating sphere?

No, an integrating sphere relies on diffuse reflection at each bounce to eventually produce uniform illumination. This is specular reflection.

2nd June 2009, 06:23 AM	#1
Dorfl Muse Join Date: Jun 2005 Location: Sweden Posts: 523	Inside a Spherical Mirror If an astronaut, equipped with a flashlight, was floating inside a sphere with a perfectly reflective surface, what would he see? Is there any software which could render his view approximately, or can it be figured out just with pen and paper?

2nd June 2009, 06:24 AM	#2
Horatius NWO Kitty Wrangler Join Date: May 2006 Location: Ottawa, ON, Canada Posts: 21,890	Reading Spider Robinson?
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2nd June 2009, 07:14 AM	#4
Just thinking Philosopher Join Date: Jul 2004 Location: New Jersey Posts: 5,169	Sounds like everything would be reflected everywhere ... including the light from the flashlight.
	__________________ Our greatest challenge is not just to ask the important questions, but to recognize the meaningless ones.

2nd June 2009, 07:46 AM	#5
Beerina Sarcastic Conqueror of Notions Join Date: Mar 2004 Location: A floating island above the clouds Posts: 23,835	As his body (and the flashlight) were the only things that absorbed the light, he would slowly heat up until he died. Assuming he didn't run out of oxygen first. Visually, he would see the room get brighter almost instantly, and probably too bright to keep his eyes open. Whether it would be so bright he'd have to close his blast shield because his eyelids and, say, sun goggles weren't enough, who knows.
	__________________ "Great innovations should not be forced [by way of] slender majorities." - Thomas Jefferson The government should nationalize it! Socialized, single-payer video game development and sales *now!* More, cheaper, better games, right? Right?

2nd June 2009, 07:49 AM	#6
Beerina Sarcastic Conqueror of Notions Join Date: Mar 2004 Location: A floating island above the clouds Posts: 23,835	His best bet would be to move away from the exact center. In this way, some of the light would miss him and keep bouncing back and forth indefinitely.
	__________________ "Great innovations should not be forced [by way of] slender majorities." - Thomas Jefferson The government should nationalize it! Socialized, single-payer video game development and sales *now!* More, cheaper, better games, right? Right?

2nd June 2009, 06:29 AM	#3
Dorfl Muse Join Date: Jun 2005 Location: Sweden Posts: 523	Originally Posted by Horatius Reading Spider Robinson? Yup. I became curious about what the answer actually was, and this seems like the likeliest place to find someone who knows.

2nd June 2009, 07:52 AM	#7
Just thinking Philosopher Join Date: Jul 2004 Location: New Jersey Posts: 5,169	Originally Posted by Beerina As his body (and the flashlight) were the only things that absorbed the light, he would slowly heat up until he died. Assuming he didn't run out of oxygen first. Visually, he would see the room get brighter almost instantly, and probably too bright to keep his eyes open. Whether it would be so bright he'd have to close his blast shield because his eyelids and, say, sun goggles weren't enough, who knows. You don't think his body could absorb the light from his flashlight quickly enough to reach some sort of equilibrium? It's likely only a single bulb of light measured in a few watts. Of course, he could always turn it off at any time. I suspect things would go completely dark very quickly should he do that. Also, we don't know how big the sphere is ... could have a radius the size of the orbit of Mercury.
	__________________ Our greatest challenge is not just to ask the important questions, but to recognize the meaningless ones. Last edited by Just thinking; 2nd June 2009 at 07:54 AM.

2nd June 2009, 07:58 AM	#8
JoeTheJuggler Penultimate Amazing Join Date: Jun 2006 Location: St. Louis Posts: 26,749	Originally Posted by Beerina His best bet would be to move away from the exact center. In this way, some of the light would miss him and keep bouncing back and forth indefinitely. Depending on the size of the sphere relative to the size of the guy, he could also lie against the surface of the sphere and block some portion of it from reflecting the light.
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2nd June 2009, 09:09 AM	#9
Unlike a Bull Thinker Join Date: Sep 2008 Posts: 188	I think there are a lot of variables that would effect what he saw. If the sphere is huge, the light would probably be so diffused that he might see a faint glow in some directions and probably blackness in others. If the sphere was pretty small (and we assume a regular flashlight, not a giant spotlight or anything) I think he would see kind of a blurry reflection of himself in some directions and a reflection of bright light (not any brighter than the bulb) in others. I think he would absorb enough of the light so that it wouldn't really be blinding, unless he lined up the flashlight so that it reflected right into his eye after only a couple reflections without being blocked by his body at all. Mirrors aren't perfectly reflective, so with each reflection some of the light would be lost (actually converted to heat). Now if we consider a "point astronaut" then (I think) more of the energy coming from the flashlight would preserved as light instead of converting to heat in which case it might get to a blinding level ... if point astronauts have eyes . I don't think the thing would heat up enough to kill the astronaut. Eventually the sphere is going to reach an equilibrium where it's emitting the same amount of energy as is coming out of the flashlight, it's just a matter of how hot it get's before that equilibrium is reached. This is dependent on how much energy is coming out of the flashlight and how well the sphere can release heat. Fortunately for the astronaut, I don't think the flashlight would really be strong enough to kill him. However, if we make the sphere sufficiently insulated ... well, it would be curtains for the astronaut. Of course the astronaut would be creating his own heat as well. Hmm, there must be some point of insulation at which if the astronaut doesn't turn on his flashlight, he won't reach a temperature to kill him, but if he does use his flashlight, he'll overheat though I'm sure it's a very fine line. Going back to the "point astronaut", when the inside of the sphere reached a point where there was enough light hitting the mirrored surface so that it's reflective inefficiency caused the sphere to lose enough heat to it's surroundings to reach equilibrium, it would no longer get any brighter inside. Adding an astronaut with physical size just gives the system another way to convert light to heat. And (I think), since there would be heat energy inside the sphere that could heat up the sphere shell, helping it to release heat, less light would have to strike it to be converted to heat to reach equilibrium. So, the smaller the astronaut the brighter the inside of the thing would be. Also, there are many people on this forum that have much better understanding of physics than I do. So please, if anything I have said isn't accurate, don't have any reservations about letting me know. edit: Missed the part about it being perfectly reflective. In which case, the mirror would not convert the light to heat. The point astronaut would result in the inside of the sphere becoming increasingly more bright until the flashlight stopped emitting light. The astronaut with physical size would be the sole converter of light to heat (assuming the inside of the sphere is a vacuum, which I think we're supposed to assume because it's in space) and his best bet would be to get as much of himself as possible pressed against the surface of the sphere so that conduction can occur. And turning off the flashlight might not be such a bad idea.
Unlike a Bull Thinker Join Date: Sep 2008 Posts: 188	Last edited by Unlike a Bull; 2nd June 2009 at 09:22 AM.

2nd June 2009, 10:22 AM	#10
Dorfl Muse Join Date: Jun 2005 Location: Sweden Posts: 523	Originally Posted by Unlike a Bull Now if we consider a "point astronaut" then (I think) more of the energy coming from the flashlight would preserved as light instead of converting to heat in which case it might get to a blinding level ... if point astronauts have eyes . Now that I think about it, it isn't necessarily the case that both of the astronaut's eyes would have at all the same view, so maybe we should assume that he is point-shaped. But then again, if he lacked extension in space there would not be anything for him to see reflected inside the sphere. Maybe we should assume that he is one-eyed.

2nd June 2009, 10:48 AM	#11
rwguinn Philosopher Join Date: Apr 2003 Location: 16 miles from 7 lakes Posts: 8,439	I'm sorry--What? There is limited energy available in the flashlight. There is no way that the mirrored sphere itself can increase that. So the max temperature increase (from the flashlight) is that which would occur if the batteries discharged instantaneously. Light brightness is proportional to the inverse of the distance traveled. Depending on the size of the sphere, the n^th reflection is going to be too dim to see, and none of them are going to blind him any worse than the flashlight itself will if he looked directly into it (and the light that hits him is blocked/ diffused, and no longer as energetic. He's in a hell of a lot more danger of overheating from his own metabolism
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2nd June 2009, 12:38 PM	#12
jasonpatterson Philanthropic Misanthrope Join Date: Apr 2009 Location: Space, The Final Frontier Posts: 2,180	Originally Posted by rwguinn I'm sorry--What? There is limited energy available in the flashlight. There is no way that the mirrored sphere itself can increase that. So the max temperature increase (from the flashlight) is that which would occur if the batteries discharged instantaneously. Light brightness is proportional to the inverse of the distance traveled. Depending on the size of the sphere, the n^th reflection is going to be too dim to see, and none of them are going to blind him any worse than the flashlight itself will if he looked directly into it (and the light that hits him is blocked/ diffused, and no longer as energetic. I agree entirely with the first part, the second part makes a false assumption. The danger to the person inside the mirror is non-existent, no more so than if you took a flashlight and shined it on a spot on your arm until the batteries died. You wouldn't overheat, you wouldn't catch fire, nothing would happen of particular importance. The brightness of light falls as the square of the distance traveled for a spherical emitter, however, in this case, assuming a perfect mirror, it would disperse, but the light would not escape, instead it would be continuously reflected back until it was absorbed. In short, it is not a spherical emitter. If the person inside the sphere was coated with perfect mirror except for the eyes, then it would brighten until the eyes were absorbing the full strength of the flashlight, close to what you would experience by putting a flashlight right in front of your eyes and turning it on. At that point the flashlight would be releasing light into the room at the same rate that the eyes were absorbing it and you'd have an equilibrium of sorts. If the person's eyes were perfect mirrors themselves (or point objects with zero surface area, or perfectly transparent, for that matter) then the person would be completely blind since it takes some absorption of light for vision to occur. That was what always bothered me about the invisible man...
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2nd June 2009, 01:35 PM	#13
Dorfl Muse Join Date: Jun 2005 Location: Sweden Posts: 523	If we assume that heating is not a problem, does anyone know what the astronaut's view would look like? Intuitively, it feels to me like he would be seeing himself, smeared over the inside of the sphere. After all, a line drawn from his eye in any direction, reflecting off the walls, would intersect his body (or the flashlight) eventually. I might be wrong though, and it is not a very detailed picture anyway. Does anyone have a better idea?

2nd June 2009, 03:02 PM	#14
rwguinn Philosopher Join Date: Apr 2003 Location: 16 miles from 7 lakes Posts: 8,439	Originally Posted by jasonpatterson I agree entirely with the first part, the second part makes a false assumption. The danger to the person inside the mirror is non-existent, no more so than if you took a flashlight and shined it on a spot on your arm until the batteries died. You wouldn't overheat, you wouldn't catch fire, nothing would happen of particular importance. The brightness of light falls as the square of the distance traveled for a spherical emitter, however, in this case, assuming a perfect mirror, it would disperse, but the light would not escape, instead it would be continuously reflected back until it was absorbed. In short, it is not a spherical emitter. If the person inside the sphere was coated with perfect mirror except for the eyes, then it would brighten until the eyes were absorbing the full strength of the flashlight, close to what you would experience by putting a flashlight right in front of your eyes and turning it on. At that point the flashlight would be releasing light into the room at the same rate that the eyes were absorbing it and you'd have an equilibrium of sorts. If the person's eyes were perfect mirrors themselves (or point objects with zero surface area, or perfectly transparent, for that matter) then the person would be completely blind since it takes some absorption of light for vision to occur. That was what always bothered me about the invisible man... I think we said the same thing.
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2nd June 2009, 03:39 PM	#15
mhaze Penultimate Amazing Join Date: Jan 2007 Location: Woo*(+-1.10)^20=AGWwoo Posts: 15,387	Originally Posted by Beerina As his body (and the flashlight) were the only things that absorbed the light, he would slowly heat up until he died. Assuming he didn't run out of oxygen first. Visually, he would see the room get brighter almost instantly, and probably too bright to keep his eyes open. Whether it would be so bright he'd have to close his blast shield because his eyelids and, say, sun goggles weren't enough, who knows. NO! The flashlight has an "ON" and an "OFF" switch. Everyone knows that "OFF" switches DARK ON. Thus the flashlight operates both as a light emitter, and a lightsucker. "OFF" mode is very efficient, allowing the flashlight to be used as a propulsion device by the astronaut in the sphere by simply pointing where he wants to go, clicking the switch, and vacuuming up photons, which creates the powerful pull forces required for intersteller travel inside a spherical mirrored device. What is done with the vacuumed up photons? They are resold on the black market - regions of the universe high in dark matter.
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2nd June 2009, 03:45 PM	#16
Piscivore Smelling fishy Join Date: May 2004 Location: Home is wherever I'm with you Posts: 26,460	I want to see Mythbusters build this.
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2nd June 2009, 04:59 PM	#17
Unlike a Bull Thinker Join Date: Sep 2008 Posts: 188	Originally Posted by mhaze What is done with the vacuumed up photons? They are resold on the black market - regions of the universe high in dark matter. I bought some of those photons once. They're not nearly as good as fresh photons. You should always buy your photons from a reputable source. By the way, I've squandered some of my precious day off doing some math on this. If we assume the flashlight uses two size D batteries and they each contain 75,000 joules of energy ( http://www.allaboutbatteries.com/Energy-tables.html we'll assume alkaline batteries although I'm sure NASA uses some crazy alien-technology, area 51 type battery. Probably Lithium-ion.) that would be some 150,000 joules together. http://www.engineeringtoolbox.com/hu...eat-d_393.html says the average human body has a specific heat of 3470 J/kgC. So if we ignore his gear and flashlight, and assume he is 70 kilograms ... his temperature will go up by about .6 degrees C. Not enough to kill him. We need bigger batteries.
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2nd June 2009, 06:38 PM	#18
Floyt Chordate Join Date: Apr 2003 Location: Cape Town! Not mugged yet. Looking for chameleons. Posts: 1,425	Originally Posted by Dorfl If we assume that heating is not a problem, does anyone know what the astronaut's view would look like? Intuitively, it feels to me like he would be seeing himself, smeared over the inside of the sphere. After all, a line drawn from his eye in any direction, reflecting off the walls, would intersect his body (or the flashlight) eventually. I might be wrong though, and it is not a very detailed picture anyway. Does anyone have a better idea? As I understand it, he wouldn't be seeing anything but a glare from any direction - the flashlight is the only emitter of light, whereas his body etc. only reflect - this would be swamped by the continuous emission from the flashlight. (Just tried to model that in a Bryce scene, with a light source and a stone texture cube inside a perfectly reflective sphere. Sure enough, once you enable total internal reflection to a high degree (obviously infinite is not available, but a couple hundred iterations can be done in acceptable time), it's all shapeless glare. I wouldn't treat that as any great evidence obviously, although Bryce's laws of optics are pretty good.)
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2nd June 2009, 06:50 PM	#19
technoextreme Illuminator Join Date: Jun 2007 Posts: 3,786	Isn't this just an integrating sphere?
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2nd June 2009, 06:50 PM	#20
Tricky Briefly immortal Moderator Join Date: Nov 2001 Location: The Group W bench Posts: 42,359	He would receive no more energy than he would if he shone the light directly on himself. The sphere only reflects energy, it does not amplify it. Seeing as the mirror is convex though, it would reflect back as a tiny point of light (which he would see in any direction he looked). Depending on the focal length of the sphere's convex side, though, he might be focusing the flashlight to a tiny point that could give him small local burns. Note also that we only need to be concerned with the first reflection of the light. After it is reflected and the distance between the source and the observation point becomes so great that the light is greatly diffused and will just provide a dim glow. Don't look at the first reflection directly though, although if my scenario is correct, the only way that could focus directly on the eyes is if he was holding the flashlight between his eyes. Anyway, that's my take.

2nd June 2009, 08:18 PM	#22
Stellafane Village Idiot. Join Date: Apr 2006 Location: Green Mountains Posts: 6,272	Originally Posted by Tricky He would receive no more energy than he would if he shone the light directly on himself. The sphere only reflects energy, it does not amplify it... This is of course correct. I think some may be confusing the situation described in the OP with that of an astronomical telescope, which as is well-known can take a pinpoint of light in the sky (often so dim it's invisible to the naked eye) and make it dazzlingly bright. But the reason a telescope can do this is because there's a lot of starlight falling on every square inch of Earth, and the telescope grabs a sizable patch of it and concentrates it into a tiny point. The total amount of theoretically available starlight is quite high because the original source of the light is extremely large and bright, and even at stellar distances produces a considerable amount of illumination falling on the Earth. The flashlight, on the other hand, produces a very limited amount of light. So even if you get every photon of light bounced back to you, it can never be brighter than the original flashlight bulb -- visible, but certainly not a blinding sheet of illumination.
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3rd June 2009, 03:37 AM	#23
Dorfl Muse Join Date: Jun 2005 Location: Sweden Posts: 523	Originally Posted by Floyt As I understand it, he wouldn't be seeing anything but a glare from any direction - the flashlight is the only emitter of light, whereas his body etc. only reflect - this would be swamped by the continuous emission from the flashlight. (Just tried to model that in a Bryce scene, with a light source and a stone texture cube inside a perfectly reflective sphere. Sure enough, once you enable total internal reflection to a high degree (obviously infinite is not available, but a couple hundred iterations can be done in acceptable time), it's all shapeless glare. I wouldn't treat that as any great evidence obviously, although Bryce's laws of optics are pretty good.) Hm, I didn't think of that. Intuitively I assumed that looking in any direction, he would see either a light beam coming from his own body, or one from the flashlight. So at worst his view would be divided into bright fields from the flashlight, and dim ones from himself. But if you say Bruce gives a uniform glare, I suppose my picture must be wrong. What if the astronaut himself were the light emitter? (Maybe Doctor Manhattan created himself a mirrory sphere, just to see what would happen.)

3rd June 2009, 06:19 AM	#24
Cuddles Decoy Moderator Join Date: Jul 2006 Location: A magical land full of pink fluffy sheeps and bunnies Posts: 16,580	Originally Posted by Unlike a Bull If we assume the flashlight uses two size D batteries and they each contain 75,000 joules of energy ( http://www.allaboutbatteries.com/Energy-tables.html we'll assume alkaline batteries although I'm sure NASA uses some crazy alien-technology, area 51 type battery. Probably Lithium-ion.) that would be some 150,000 joules together. http://www.engineeringtoolbox.com/hu...eat-d_393.html says the average human body has a specific heat of 3470 J/kgC. So if we ignore his gear and flashlight, and assume he is 70 kilograms ... his temperature will go up by about .6 degrees C. Not enough to kill him. We need bigger batteries. I don't think that's correct. You're assuming that his body simply absorbs all the energy. However, at the same time it will be acting as a black body emitter. In fact, the astronaut is likely to be by far the biggest radiation source present. Assuming he has enough food, he'll eventually die once the inside of the sphere has heated up past 37^o and he can no longer regulate his body temperature.
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3rd June 2009, 07:26 AM	#25
dogjones Graduate Poster Join Date: Oct 2005 Location: Bermuda Posts: 1,281	Originally Posted by Unlike a Bull I bought some of those photons once. They're not nearly as good as fresh photons. You should always buy your photons from a reputable source. Maudsley does a good line.
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3rd June 2009, 07:51 AM	#26
Unlike a Bull Thinker Join Date: Sep 2008 Posts: 188	Originally Posted by Cuddles I don't think that's correct. You're assuming that his body simply absorbs all the energy. However, at the same time it will be acting as a black body emitter. In fact, the astronaut is likely to be by far the biggest radiation source present. Assuming he has enough food, he'll eventually die once the inside of the sphere has heated up past 37^o and he can no longer regulate his body temperature. You are correct that I am incorrect. I was just thinking about worst case (hypothetical) scenario where all the energy from the flashlight is converted to heat and all is transferred to his body. If this worst case scenario won't kill him then the lesser, realistic ones won't either. I'm not sure if his metabolism would be enough to kill him either though. It is specified that the sphere reflects light perfectly, but nothing is said about it's heat conductivity. Therefore we're free to speculate! If the sphere is a perfect insulator, then yes his metabolism will eventually kill him. If, however, the sphere allows heat to be released to the surroundings then it's just a matter of how hot the thing will get before equilibrium is reached. also, I don't think he would lose his ability to regulate temperature when the sphere reaches 37 C. I know he would lose his ability to radiate heat to his environment, but he could get creative. Once he started getting warm he would start sweating. He would be able to regulate temp through sweat for a while, but the air in his suit would become warm and humid pretty quickly. But, by venting this humid air into the sphere, he would be removing heat from himself and putting it into his environment. This air would then be replaced by whatever kind of breathing system he had. He would be able to do this for a while, since all he would need is a pressure difference to vent the air. please note, I'm not saying that a 37 C astronaut could make his surroundings greater than 37 C, but by moving mass from himself to his surroundings, he can remove heat from himself.
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3rd June 2009, 07:57 AM	#27
Cuddles Decoy Moderator Join Date: Jul 2006 Location: A magical land full of pink fluffy sheeps and bunnies Posts: 16,580	Originally Posted by Unlike a Bull If, however, the sphere allows heat to be released to the surroundings then it's just a matter of how hot the thing will get before equilibrium is reached. please note, I'm not saying that a 37 C astronaut could make his surroundings greater than 37 C, but by moving mass from himself to his surroundings, he can remove heat from himself. Well, I assumed that since we were dealing with an astronaut that he'd be floating in a perfect vacuum. If you allow atmosphere inside then that changes things a bit, and by playing with the conditions inside and outside the sphere you can come up with pretty much any outcome you like.
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3rd June 2009, 09:19 AM	#28
Unlike a Bull Thinker Join Date: Sep 2008 Posts: 188	Originally Posted by Cuddles Well, I assumed that since we were dealing with an astronaut that he'd be floating in a perfect vacuum. I'm operating under the same assumption (well, maybe not a PERFECT vacuum). I meant that the sphere would be able to radiate heat away from itself. When I talked about its conductivity I meant it's ability to transfer heat from it's inside edge to it's outside edge so that the energy could be radiated away, not that it would be conducting heat into some medium outside of it. Sorry if I wasn't clear enough. Quote: If you allow atmosphere inside then that changes things a bit Why wouldn't you allow atmosphere in the sphere if it's vented from the astronauts suit? Quote: and by playing with the conditions inside and outside the sphere you can come up with pretty much any outcome you like. Pretty much. This is because we weren't given enough information in the OP, because the OP was about what the astronaut would see, not how hot he would get.
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3rd June 2009, 09:38 AM	#29
Cuddles Decoy Moderator Join Date: Jul 2006 Location: A magical land full of pink fluffy sheeps and bunnies Posts: 16,580	Originally Posted by Unlike a Bull I'm operating under the same assumption (well, maybe not a PERFECT vacuum). I meant that the sphere would be able to radiate heat away from itself. When I talked about its conductivity I meant it's ability to transfer heat from it's inside edge to it's outside edge so that the energy could be radiated away, not that it would be conducting heat into some medium outside of it. Sorry if I wasn't clear enough. But if there's a vacuum inside the sphere then it can never absorb any heat. It's a perfect reflector, remember, so it can't absorb any radiation. An atmosphere would allow conduction, but if you get rid of that there's nothing. Quote: Why wouldn't you allow atmosphere in the sphere if it's vented from the astronauts suit? Because, assuming the question was about what would happen in a vacuum, it would be changing the question. It's like starting with the question asking about a perfect reflector and then saying that the astronaut could throw something at it to break it. That sort of thinking is great for silly lateral thinking questions, but is utterly pointless when applied to thought experiments trying to answer a specific question. For my part, I wouldn't allow atmosphere in the sphere if it's vented from the suit because I was thinking about what would happen in a vacuum. As I said, if you allow an atmosphere then you can come up with pretty much any result depending on what assumptions you make, but in that case it makes no difference where the atmosphere comes from, so it's completely pointless to wonder about different cooling systems the astronaut might have.
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3rd June 2009, 10:33 AM	#30
Unlike a Bull Thinker Join Date: Sep 2008 Posts: 188	Originally Posted by Cuddles But if there's a vacuum inside the sphere then it can never absorb any heat. It's a perfect reflector, remember, so it can't absorb any radiation. An atmosphere would allow conduction, but if you get rid of that there's nothing. Oh! For some reason I was thinking perfectly reflective only in regards to visible light. I see my error now. Thanks.
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4th June 2009, 06:52 AM	#31
Dan O. Philosopher Join Date: Feb 2007 Posts: 8,744	Originally Posted by Tricky Don't look at the first reflection directly though, although if my scenario is correct, the only way that could focus directly on the eyes is if he was holding the flashlight between his eyes. The first reflection will create a somewhat distorted and blurred image at a point that is an equal distance on the opposite side of the center of the sphere. The closer that the source is to the center, the sharper the image will be. If the astronaut is at the location of the first image, light would be seen coming from all directions except where the astronaut's own shadow blocked the light. The intensity of the light at the image will follow the inverse square law with the distance measured from the image not the original source. The maximum intensity at the image cannot exceed the intensity of the source. However, since the image is not protected by a bulb, it is possible to get much closer to it. If the astronaut is closer to the center than the source and on the line through the source and the sphere's center then the astronaut will not see the first image of the source except for some extra light coming from directly behind the source. The astronaut's own shadow will be blocking the light that would have created the image. Anything inside the sphere that is illuminated (such as the astronaut) will be a secondary light source and will also produce an image opposite the center. The astronaut will see an image of himself but without the reversal that you see in a mirror. Also unlike an image produced by a flat mirror, it is possible to pass through this image by passing through the spheres center.
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4th June 2009, 11:36 AM	#32
Dorfl Muse Join Date: Jun 2005 Location: Sweden Posts: 523	Originally Posted by Dan O. The first reflection will create a somewhat distorted and blurred image at a point that is an equal distance on the opposite side of the center of the sphere. The closer that the source is to the center, the sharper the image will be. If the astronaut is at the location of the first image, light would be seen coming from all directions except where the astronaut's own shadow blocked the light. The intensity of the light at the image will follow the inverse square law with the distance measured from the image not the original source. The maximum intensity at the image cannot exceed the intensity of the source. However, since the image is not protected by a bulb, it is possible to get much closer to it. If the astronaut is closer to the center than the source and on the line through the source and the sphere's center then the astronaut will not see the first image of the source except for some extra light coming from directly behind the source. The astronaut's own shadow will be blocking the light that would have created the image. Anything inside the sphere that is illuminated (such as the astronaut) will be a secondary light source and will also produce an image opposite the center. The astronaut will see an image of himself but without the reversal that you see in a mirror. I have difficulty visualizing that, but it does sound cool. Thank you very much, I had been wondering about it for a few years now. Quote: Also unlike an image produced by a flat mirror, it is possible to pass through this image by passing through the spheres center. [Prince of Persia] Sheathe your sword and pass through your mirror image... It took me weeks to figure that out! [/Prince of Persia]

4th June 2009, 12:25 PM	#33
Timothy Muse Join Date: Feb 2005 Posts: 544	Originally Posted by technoextreme Isn't this just an integrating sphere? No, an integrating sphere relies on diffuse reflection at each bounce to eventually produce uniform illumination. This is specular reflection.
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