Star triangle paradox

Magical Realist

Magical Realist

Valued Senior Member
Picture three stars forming a perfect triangle in space. One is our own sun. Let's say the three stars are all at the same distance from each other--100 light years. Now from our point of view the two stars are both 100 light years away. So to us they'd be existing at the same time to each other-- both exactly 100 years ago. BUT..from the perspective of either of those two stars, the other star would NOT be existing at the same time but 100 years in the past. So which is it? Are the stars existing at the same time? Or at different times? Or both?
 
Magical Realist said:
Picture three stars forming a perfect triangle in space. One is our own sun. Let's say the three stars are all at the same distance from each other--100 light years. Now from our point of view the two stars are both 100 light years away. So to us they'd be existing at the same time to each other-- both exactly 100 years ago. BUT..from the perspective of either of those two stars, the other star would NOT be existing at the same time but 100 years in the past. So which is it? Are the stars existing at the same time? Or at different times? Or both?
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Ask again in a hundred years :D

Assuming they didn't blow up in the last hundred years, they both exist right now. We just see them as they were a hundred years ago.
They aren't in the past just because their light takes a hundred years to reach us, which is what you seem to suggest.
 
They all exist at the same time. We just seem them later.

(Similar question - if a live concert is broadcast Sunday, and your friend watches a re-run of it Monday, and you watch a re-run of it Tuesday - when did the concert really occur? Is it all really existing at the same time, or in three different times?)
 
Magical Realist said:
BUT..from the perspective of either of those two stars, the other star would NOT be existing at the same time but 100 years in the past. So which is it?
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Neither of the stars would have a perspective consisting of visual image and thoughts about the other star's existence status. Reception alone of energies from distant sources is not perception and judgement. While it's unlikely that cosmic disaster would befall any stable star or it would cross paths with a black hole within a century, there would still be a degree of speculation involved even if human observers could be available around the other two to provide either a belief or a conclusion.

But any triangular-like appearance of the three stars would exist currently, derived from light converging at a location on Earth, affecting retinal tissue whose stimulations brain processes eventually infer to be such a POV-dependent sky configuration. In the distant past, however, understandings like "light-years" and the tiny lights being huge fusion furnaces would not be part of the conceptual add-ons to the phenomenal manifestation. Indeed, a later geometrical classification like triangle might not even have an analogous substitute invented yet, though cognising it as "spear-point" would surely suffice.
 
Magical Realist said:
Not so fast:

The Relativity of Simultaneity
http://www.fourmilab.ch/documents/RelativityOfSimultaneity/
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Your example has nothing to do with the Relativity of Simultaniety.

Your three Sun's are not moving relative to each other. So let's say that it is 2011 on the Earth his looks at both the other Sun's (with a real powerfull telescope) to see their calendars read 1911. However he also nows that each sun is 1 hundred lightyears away and that one hundred years passed on both the Earth and each of the other sun's, meaning that at the moment he looks at the other Sun's it is 2011 at each of those suns also. Thsi wold be the same thing that either of the two suns would see looking at the Earth or each other.

The Relativity of Simultaneity deals with relative motion.

Let's add an observer traveling in a spaceship towards one of the suns at some fraction of c. He passes the Earth at the instant you look at this Sun and see its calendar reading of 1911. He is looking at the Sun too, and since you both see the same light, he also sees that the sun's calendar reads 1911 ( and being right next to the Earth will note that its calendar reads 2011.

But because he has a realtive velocity with respect to the Sun, he will not conclude that 100 years passed for the Sun in the time it took the light to reach him, he will conclude that it took more than 100 years and that it is actually later than 2011 at the Sun during the instant he passes the Earth.

This is the Relativity of Simultaneity. An observer on the Earth will conclude that it the same time/date at Earth and the Sun and the obseerver in the rocket will conclude that it is not.
 
Janus58 said:
Your example has nothing to do with the Relativity of Simultaniety.

Your three Sun's are not moving relative to each other. So let's say that it is 2011 on the Earth his looks at both the other Sun's (with a real powerfull telescope) to see their calendars read 1911. However he also nows that each sun is 1 hundred lightyears away and that one hundred years passed on both the Earth and each of the other sun's, meaning that at the moment he looks at the other Sun's it is 2011 at each of those suns also. Thsi wold be the same thing that either of the two suns would see looking at the Earth or each other.

The Relativity of Simultaneity deals with relative motion.

Let's add an observer traveling in a spaceship towards one of the suns at some fraction of c. He passes the Earth at the instant you look at this Sun and see its calendar reading of 1911. He is looking at the Sun too, and since you both see the same light, he also sees that the sun's calendar reads 1911 ( and being right next to the Earth will note that its calendar reads 2011.

But because he has a realtive velocity with respect to the Sun, he will not conclude that 100 years passed for the Sun in the time it took the light to reach him, he will conclude that it took more than 100 years and that it is actually later than 2011 at the Sun during the instant he passes the Earth.

This is the Relativity of Simultaneity. An observer on the Earth will conclude that it the same time/date at Earth and the Sun and the obseerver in the rocket will conclude that it is not.
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No..motion is not necessary. Any change in space is a change in time. As in "spacetime"? And since you obviously didn't read the article, I'll quote from it:

"Some physicists prefer to reserve the term "relativity of simultaneity" for cases where observers are in motion relative to one another and the effects of special relativity obtain. In a case like the example above, where all the observers and sources are at rest with respect to one another, it is possible, using Einstein's definition of simultaneity, for spatially separated observers to synchronise their clocks and define simultaneity in terms of the spacetime interval between events. When observers are in relative motion, however, it is impossible, even in principle, to synchronise their clocks, so no definition of simultaneity is possible. But to me, the phrase "relativity of simultaneity" means precisely what it says, notwithstanding relativistic effects or their absence. In this case, three observers of the same two events see three different orders in which they appeared to occur from their particular vantage points; hence their perception of simultaneity is relative even though it is entirely due to light travel time instead of motion."
 
Nevermind. I looked this up and couldn't find anything supporting the author's thesis. Guess we have to look out for crackpots with their own personal theories. So you're right--it only pertains between objects that are stationary and objects that are moving. This comes as a great relief to me actually--to know that the universe exists all in one time frame and that all things exist at the same time regardless of what light shows us. I mistakenly assumed the spacetime continuum itself kept things apart at different times just as it keeps things apart at different places. Sometimes it's good to be wrong! ;)
 
I don't fucking get it. Stars are all moving(really fast actually). We are seeing the light from 100 years ago. I suspect it's not to hard to guess where they would REALLY be sitting right NOW relative to us after a few months observation.
 
Magical Realist:

You seem to be confusing when stars exist with when we see light from them. The two things are not the same.

It doesn't have to be stars, either. Look around the room you're in. Can you see a door? You're actually seeing that door as it was a few nanoseconds ago. But I don't think you'll argue that it doesn't exist right now.
 
James R said:
Magical Realist:

You seem to be confusing when stars exist with when we see light from them. The two things are not the same.

It doesn't have to be stars, either. Look around the room you're in. Can you see a door? You're actually seeing that door as it was a few nanoseconds ago. But I don't think you'll argue that it doesn't exist right now.
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But it seems you're saying there's actually two stars, or doors. One that I see and another one that I'll never see. Actually I find that proposition attractive but only in a Kantian sense. For him things exist, but we never experience them as they are in-themselves, only as appearances. What I'M saying is that the light is revealing to us exactly what's there, a star or a door existing in the past. Can we prove or disprove our positions either way?
 
Magical Realist,

What proposition are you trying to prove or disprove, exactly?
 
James R said:
Magical Realist,

What proposition are you trying to prove or disprove, exactly?
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I'm simply saying that light shows us what is really there--a star or a door existing in the past. It isn't showing us the illusion of a star or door existing in the past.
 
Magical Realist said:
But it seems you're saying there's actually two stars, or doors. One that I see and another one that I'll never see. Actually I find that proposition attractive but only in a Kantian sense. For him things exist, but we never experience them as they are in-themselves, only as appearances. What I'M saying is that the light is revealing to us exactly what's there, a star or a door existing in the past. Can we prove or disprove our positions either way?
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It seems that you are saying that if you can't see it it isn't there.
 
billvon said:
No, light shows us what was there when the light left the object.
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Can you prove light shows us what WAS there instead of what IS there? It seems to assume a perceptual state of the star as existing without it's light reaching us. IOW, a star abstracted from it's starlight--at an instant in time and so "in the dark" so to speak. Do such dark and totally imperceivable stars exist? How would we prove it?


In point of fact, we CAN imagine flying towards the star at the speed of light (but no faster as then we'd be going back into time.). But at no point do we encounter a dark simultaneous star separate from it's light. All we see is a star becoming less and less in our past until we reach it's point in spacetime where it is simulataneous with us. Where was dark star that was supposed to be existing separately from it's light? It was never there.
 
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