# Gravitational lensing

1. Sep 12, 2015

### Varun Lall

Is the phenomenon of gravitational lensing caused due to the particle nature of light or due to its wave nature? If not so, what is the correct explanation?

2. Sep 12, 2015

### Staff: Mentor

That is not a well-defined question. There is no "either/or". There are experiments where a description of light via particles can be useful, there are experiments where a description as wave can be useful, there are experiments where neither is useful and where you have to consider it as quantum-mechanical thing.

General relativity describes gravity as curved spacetime. In this spacetime, light travels in a straight line. It's not the path of the light that is curved, it is spacetime.
Note: this is just a description. A very good one, however.

3. Sep 12, 2015

### Varun Lall

I couldn't understand what you meant by that-"It's not the path of the light that is curved, it is spacetime."

4. Sep 12, 2015

### Varun Lall

This effect will only be visible when the path of light rays has been altered, and that cannot happen until light rays themselves have been bent(as their is no refractory substance present)

5. Sep 12, 2015

### Chalnoth

The wave/particle nature of light just doesn't come into it. Gravitational lensing is a gravitational phenomenon, and the relevant property of light that makes gravitational lensing work the way it does is the fact that light moves at speed c.

6. Sep 13, 2015

### Staff: Mentor

It's analogous to the surface of the Earth. If you and I start off at the equator and head due north, we will find that, although both of us have continued in a straight line, we are somehow getting closer together. This is because the surface of the Earth is curved and straight paths that started out as parallel may end up curving towards or away from each other.

7. Sep 13, 2015

### Varun Lall

Thank you. I've understood it now. It doesn't matter how light is interacting(with particle/wave nature), because it is the curvature of spacetime itself that is responsible for the phenomenon of gravitational lensing, isn't it?

8. Sep 13, 2015

### Staff: Mentor

That's right.

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