bending light

Discussion of theories involving time as a dimension, time travel, relativity, branes, and so on, usually applying to the "real" universe which we live in.

bending light

Postby papernuke » Fri Apr 06, 2007 3:26 pm

why does light bend around an object that is massive? is it because the gravity distorts the space-time near it??
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Postby houserichichi » Fri Apr 06, 2007 6:29 pm

Light only appears to bend. Gravity warps spacetime which makes it appear to an observer that light bends around an object when, in fact, all it's doing is following a straight line (what we call a geodesic) through curved space.
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Postby papernuke » Sat Apr 07, 2007 3:17 am

Then why is the space curved around massive objects in space?
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Postby wendy » Sat Apr 07, 2007 7:21 am

light does not bend in space. It goes straight ahead. Moreover, space does not 'bend'.

However, the curvature of space near a massive object is graded to produce smaller (ie more to -inf) curvature near the massive object. The effect of this is that the circumference of the circle, divided into two parts, gives a smaller angle towards the massive object, and a straight line tends to deflect towards the massive object, relative to the angles.

Therefore, light appears to bend, relative to the overlying euclidean metric.
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Postby Nick » Sun Apr 08, 2007 11:28 am

wendy wrote:light does not bend in space. It goes straight ahead. Moreover, space does not 'bend'.

However, the curvature of space near a massive object is graded to produce smaller (ie more to -inf) curvature near the massive object. The effect of this is that the circumference of the circle, divided into two parts, gives a smaller angle towards the massive object, and a straight line tends to deflect towards the massive object, relative to the angles.

Therefore, light appears to bend, relative to the overlying euclidean metric.


Wow. :o
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Postby Asymptote » Sat Apr 21, 2007 1:44 pm

PaperNuke wrote:Then why is the space curved around massive objects in space?


That was Einstein's great discovery: that the presence of mass causes curvature in space. Actually, I haven't heard any really good explanations for why this should happen, but I think it's just a property of the structure of space and time.
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Postby pat » Mon Apr 23, 2007 1:18 am

Nick wrote:Wow. :o


I was also going to say "Wow", but maybe not for the same reason. That's the most concise and most accurate description that I've seen of the phenomena... and all in words that I understand. Thank you, wendy.

Asymptote wrote:
PaperNuke wrote:Then why is the space curved around massive objects in space?

hat was Einstein's great discovery: that the presence of mass causes curvature in space. Actually, I haven't heard any really good explanations for why this should happen, but I think it's just a property of the structure of space and time.


Agreed, there is no explanation of *why* this should happen. Newton's laws of motion and law of gravity provide no explanation either. Quantum theory provides no reason why (though string theorists are trying). Science generally doesn't answer "why". It generally answers either "how" or "how much". In this case, it's "how much".

Einstein's great insight was that being in a gravitational field feels like accelerating. He then said, "How could that be true?" Then, he followed it to the only conclusion.... curved space-time.
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Postby Asymptote » Mon Apr 23, 2007 12:49 pm

Personally, I think a real holy grail of science would be a justification for a physical laws, the answer to the question "Why should it be so?" But I digress.
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Postby bo198214 » Mon Apr 23, 2007 4:22 pm

From a philosophical standpoint I would rather say its not true.
It shouldnt be so, it is merely so.
I can think of many worlds with completely different laws, that would work as worlds too. So to say by accident/incident you have to deal with *this* world.
So there is nothing to answer a "why" because the statement is false.
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