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If the universe is shaped just right, can the same source of light appears as two different stars in the sky?
My understanding is that we don't know the shape of the universe. It is possible that it is shaped such that one could travel in the same direction for a long period of time and eventually return to the same location.
If this is the case, it seems reasonable that we might be able to see the same star in two locations in the sky at the same time. However, given the distance from the star to Earth is likely different for the two paths, the stars will appear to have different ages, so we probably would not be able to determine the duplication. This argument seems specious to me. What is wrong with my way of looking at it?
If this is the case, it seems reasonable that we might be able to see the same star in two locations in the sky at the same time. However, given the distance from the star to Earth is likely different for the two paths, the stars will appear to have different ages, so we probably would not be able to determine the duplication. This argument seems specious to me. What is wrong with my way of looking at it?
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Ok, so I wrote up a HUGE answer to this explaining the circumstances with which your theories could be true including light bending due to black holes and the black hole at the center of the universe... However, Mahalo failed when I submitted it and it's all lost.
Summation of my message: given the shape of the universe, it would be possible to see multiple visions of the same source. The universe would have to be loop shaped (cylindrical), your theory would indeed be true as far as seeing multiple "stars" from the same source. I have a theory that an infinite loop would likely cause this as well. Of course, the cylindrical loop would have to be rather "close" perspectively.
After all of my theorizing and explanation, I did a search for "universe shape infinite loop" resulted in the source link that supported my answer (and your question, in some manner).
Take care.
Summation of my message: given the shape of the universe, it would be possible to see multiple visions of the same source. The universe would have to be loop shaped (cylindrical), your theory would indeed be true as far as seeing multiple "stars" from the same source. I have a theory that an infinite loop would likely cause this as well. Of course, the cylindrical loop would have to be rather "close" perspectively.
After all of my theorizing and explanation, I did a search for "universe shape infinite loop" resulted in the source link that supported my answer (and your question, in some manner).
Take care.
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I would love to have seen your "huge" answer, but this answer best addresses my question because it is applicable to the details of the light coming from the same source in two different directions while not being distracted with the phenomenon of lensing. Additionally, example of cylinder is helpf
No, you are having problems of scale. Also, the questions about interpreting the shape of the universe are not really like that. Light can be turned/bent by gravity such as by passing near a black hole. One can imagine a remote likelihood that some arrangement of stars and black holes could send light from a star to earth from two directions. However, if the black holes were near the star, the angle would be too narrow and it would appear as one on earth. If the black holes were far enough away from the star to provide enough angle to detect, then the amount of light would be too small and would not appear as a star. At least, I think that's what you are asking. I am talking about stars that can be seen and distinguished by the naked eye, not imaging effects that can be detected only by instruments or giant radio telescopes.
Yes! It happens all the time...
You must have seen the Star Wars Episode 4 (A New Hope) scene where Luke is looking towards the twin suns of Tatooine, right? That was NOT (I repeat NOT) a special effect!
That actually happens when our sun is low in the horizon in Tanzania (I believe that's where they filmed). The Earth's atmosphere will make that twin sun effect.
So, to answer your question, yes, a star (our sun) CAN look as if it is in two different places in the sky.
You must have seen the Star Wars Episode 4 (A New Hope) scene where Luke is looking towards the twin suns of Tatooine, right? That was NOT (I repeat NOT) a special effect!
That actually happens when our sun is low in the horizon in Tanzania (I believe that's where they filmed). The Earth's atmosphere will make that twin sun effect.
So, to answer your question, yes, a star (our sun) CAN look as if it is in two different places in the sky.
source(s):
I can't find the source. But I really, really remember this being true. (really!)
I can't find the source. But I really, really remember this being true. (really!)
An illustration of this phenomenon:
http://bovitz.com/photo/traditional/jpgphotos/2006/TwinSuns2.jpg
(Rowland Heights, California)
and actually, most scenes taking place on Tatooine were shot in Tunisia, in particular at a location called Tataouine (hence the name in Star Wars)
http://bovitz.com/photo/traditional/jpgphotos/2006/TwinSuns2.jpg
and actually, most scenes taking place on Tatooine were shot in Tunisia, in particular at a location called Tataouine (hence the name in Star Wars)
Anything is possible, almost.
Yes. Gravtiational lensing can cause this.
A light source on the far side of a massive object can have its light bent around the massive object.
This could cause a star (alignment is critical for this) to appear as two (or more) seperate points of light.
NASA wrote a nice explanation, with drawings to illustrate the concept after the Hubble space telescope took a picture of very distant galaxies using this phenemon.
A light source on the far side of a massive object can have its light bent around the massive object.
This could cause a star (alignment is critical for this) to appear as two (or more) seperate points of light.
NASA wrote a nice explanation, with drawings to illustrate the concept after the Hubble space telescope took a picture of very distant galaxies using this phenemon.
Light being bent around a black hole is not the same as seeing the same source twice. When this happens two *different* light rays come out of the star and converge on an observer after being lensed by the gravitationally massive object. This isn't really the same photon twice.
MIBCHRONICLES has "refuted" my statement, erroneously.
fact: The post did not ask "can ONE PHOTON be viewed twice".
I fail to see where you got that stipulation.
Let's check the conditions. The O.P. Asked "If the universe is shaped just right, can the same source of light appears as two different stars in the sky?"
Now a star, as a source of light, emite billions of photos per second. No where do I see anyone asking can a single photon be viewed as coming from different points. I think he is asking "Do we live in a closed universe, and can space fold back upon itself?" which mirrors the torus conundrum that a multi-domensional universe suggests.
But, to focus on the original question, a single star _CAN_ be seen in two vectors (different points in the sky) if a gravitation lense lies between the observer and that distant star (or galaxy!)
fact: The post did not ask "can ONE PHOTON be viewed twice".
I fail to see where you got that stipulation.
Let's check the conditions. The O.P. Asked "If the universe is shaped just right, can the same source of light appears as two different stars in the sky?"
Now a star, as a source of light, emite billions of photos per second. No where do I see anyone asking can a single photon be viewed as coming from different points. I think he is asking "Do we live in a closed universe, and can space fold back upon itself?" which mirrors the torus conundrum that a multi-domensional universe suggests.
But, to focus on the original question, a single star _CAN_ be seen in two vectors (different points in the sky) if a gravitation lense lies between the observer and that distant star (or galaxy!)
If the universe is shaped like a three dimensional torus, then the star's light can appear to come from two different places.
But we've pretty much proved the universe is flat (see very short summary in the link), which eliminates the three dimensional torus and a bunch of other shapes that would make that happen as the shape of the universe.
So in real life, no, we can't see the same star on the left and right.
But we've pretty much proved the universe is flat (see very short summary in the link), which eliminates the three dimensional torus and a bunch of other shapes that would make that happen as the shape of the universe.
So in real life, no, we can't see the same star on the left and right.
It is possible to travel in the same direction for a long time and end up in the same spot. However this depends on what you mean by in the same direction. Time and space are not absolute, and therefore there is no absolute direction. If one travels around the world it would appear to him as if he is constantly traveling in the same direction, but he ends up in the same place as he started. When light bounces off a mirror, it is unaware of any change in direction, and it can return to the same place it started. The light only changes direction relative to an observer. Same thing with gravitational lensing. The light does not notice any change in direction, but the light changes direction relative to the observer, and the image is duplicated.
http://chandra.harvard.edu/photo/2006/1e0657/1e0657_lens_ill.jpg
http://chandra.harvard.edu/photo/2006/1e0657/1e0657_lens_ill.jpg
john rosenbergs answer is correct, we use this effect to figure out where black holes are
I'm gonna have to disagree with everyone so far on this page. You cannot observe the same photon from two different directions.
When you talk about gravitational lensing you are talking about continuously deforming the picture of a star until it becomes two stars instead of one. But remember here that a star is *not* a point object, there are many many many photons flying off it's finite surface.
As far as observing the same photon twice on a curved space-time background? Yes you could observe the same photon twice, but never at the same time. If you talk about a source of photons then you could see both beams, but they would have different phases.
Now to answer the question: kpolich you are absolutely right. The stars would necessarily have to have different ages. Sure they could be very close but we wouldn't see the *exact* same picture twice. Realistically though, we are living inside our own "Hubble sphere". This is a distance from Earth dictated by the expansion of the universe beyond which we simply cannot see. The universe expands in such a way that object which are farther from us move away from us faster than objects that are close. At some point objects are so far that they move faster than the speed of light and we cannot see them. This is because any photon they emit will never reach us. Since our Hubble sphere is smaller than the known universe, we will not be able to see duplicate stars in the sky. Simply, the universe expands faster than it is possible for a single photon to do a round trip.
PS: If you're curious about the objects moving away from us faster than the speed of light, this is perfectly permissible. The Hubble sphere creates an "outer" event horizon which does not permit communication faster than the speed of light and so nothing is violate. Interestingly, this even horizon is also subject to the black hole information loss paradox.
When you talk about gravitational lensing you are talking about continuously deforming the picture of a star until it becomes two stars instead of one. But remember here that a star is *not* a point object, there are many many many photons flying off it's finite surface.
As far as observing the same photon twice on a curved space-time background? Yes you could observe the same photon twice, but never at the same time. If you talk about a source of photons then you could see both beams, but they would have different phases.
Now to answer the question: kpolich you are absolutely right. The stars would necessarily have to have different ages. Sure they could be very close but we wouldn't see the *exact* same picture twice. Realistically though, we are living inside our own "Hubble sphere". This is a distance from Earth dictated by the expansion of the universe beyond which we simply cannot see. The universe expands in such a way that object which are farther from us move away from us faster than objects that are close. At some point objects are so far that they move faster than the speed of light and we cannot see them. This is because any photon they emit will never reach us. Since our Hubble sphere is smaller than the known universe, we will not be able to see duplicate stars in the sky. Simply, the universe expands faster than it is possible for a single photon to do a round trip.
PS: If you're curious about the objects moving away from us faster than the speed of light, this is perfectly permissible. The Hubble sphere creates an "outer" event horizon which does not permit communication faster than the speed of light and so nothing is violate. Interestingly, this even horizon is also subject to the black hole information loss paradox.
source(s):
degree in math and physics
The Black Hole War - Leonard Susskind
A Brief History of Time - Stephen Hawking
degree in math and physics
The Black Hole War - Leonard Susskind
A Brief History of Time - Stephen Hawking
I have a big problem with this statement: "As far as observing the same photon twice on a curved space-time background? Yes you could observe the same photon twice, but never at the same time. If you talk about a source of photons then you could see both beams, but they would have different phases."
First, lets check the definition of a "Photon".
"About" has a nice description at http://physics.about.com/od/lightoptics/f/photon.htm
Note that a photon is destroyed when it is "detected" by the eye, camera or absorbing surface it falls upon.
You seem to be talking more about a ray, such as a laser, which of course is a stream of millions of photons moving is a synchronized wave along a non-diverging path. But even then, a ray is a one directional vector! You could never see the same ray (or photon!) more than once, ever.
Think of it this way: The first time you "see" it it is destroyed. So there can not ever be a second time.
Anyway, not to split hairs, but one photon has one existence and is destroyed by the process of being observed, so no photon may ever be viewed twice.
First, lets check the definition of a "Photon".
"About" has a nice description at http://physics.about.com/od/lightoptics/f/photon.htm
Note that a photon is destroyed when it is "detected" by the eye, camera or absorbing surface it falls upon.
You seem to be talking more about a ray, such as a laser, which of course is a stream of millions of photons moving is a synchronized wave along a non-diverging path. But even then, a ray is a one directional vector! You could never see the same ray (or photon!) more than once, ever.
Think of it this way: The first time you "see" it it is destroyed. So there can not ever be a second time.
Anyway, not to split hairs, but one photon has one existence and is destroyed by the process of being observed, so no photon may ever be viewed twice.
I agree. All experiments I'm aware of necessarily destroy the photon they observe. However, the key to answering this question is not to permit the photon to *interact* with one point in space at the same time from two different direction. There just needs to be two photons for that to happen.
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Seemed to be a bit odd, since I'd never had the answer submission page do that upon submission before; however, the other sites I was browsing were working fine. Perhaps it was a timeout of some sort.