Gravity's Pull on Photons: Explained

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    Gravity Photons
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Discussion Overview

The discussion revolves around the interaction of gravity with photons, particularly how gravity affects the path of light and the implications of Planck length in this context. Participants explore concepts from general relativity and the nature of spacetime, as well as the potential energy of photons at the Planck scale.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that while gravity pulls objects down, photons also experience this pull, but their travel distance is much greater before being affected by gravity.
  • Another participant discusses the bending of light in the context of general relativity, noting that both photons and massive objects travel in "straight" lines in curved spacetime, questioning the relevance of Planck units to this phenomenon.
  • A participant proposes an analogy between Planck lengths and pixels on a monitor, suggesting that if space is quantized at the Planck scale, photons might "skip" between these lengths rather than moving smoothly.
  • Another participant agrees with the previous point, elaborating on the implications of curved spacetime and expressing appreciation for the clarification provided.
  • One participant mentions that photons with wavelengths around the Planck length would possess enormous energy, potentially enough to initiate a big bang, contrasting this with the much larger wavelengths of typical photons, including gamma rays.
  • A participant notes that a gravitating body must be very dense to prevent photons from escaping, indicating that on Earth, photons can escape easily but appear to stretch in the gravitational field.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the relationship between gravity and photons, with some agreeing on the implications of curved spacetime while others question the relevance of Planck length. The discussion remains unresolved with multiple competing views present.

Contextual Notes

Some assumptions about the nature of spacetime and the behavior of photons under gravity are not fully explored, and the discussion includes speculative analogies that may not have consensus among participants.

bassplayer142
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If you throw a ball gravity pulls it down. The harder you throw it the farther it will go but it is still constantly being pulled down by gravity. If you look at a photon even it will get pulled down by gravity but the photon will go a lot farther before it would hit the ground. Now if you were to view this photon on a very short interval wouldn't the photon be going in a straight line and then kind of step down towards the ground due to Planck length. Just think of the floor and ceiling functions in math. I don't understand how the Planck length could even make sense with this because the photon can't be moving slightly down on anything smaller then the Planck length. As usual, I probably just don't know everything about the subject and have a lack of understanding. Thanks in advanced.
 
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the fact that, in our Euclidian coordinate system, we observe the bending of a ray of light toward a massive object (due to gravity, but in GR they would say that both the photon and ball are traveling in a "straight" line and it is the space-time around it that is curved, due to the massive object). but i don't think that Planck units have anything to do with this. what's the connection?
 
rbj said:
the fact that, in our Euclidian coordinate system, we observe the bending of a ray of light toward a massive object (due to gravity, but in GR they would say that both the photon and ball are traveling in a "straight" line and it is the space-time around it that is curved, due to the massive object). but i don't think that Planck units have anything to do with this. what's the connection?
I think what he's asking is, supposing that in the same way that pixels make up a monitor, Planck lengths of space make up our world, wouldn't a photon seem to suddenly skip down into the next Planck length instead of moving in a smooth curve a la macroscopic physics?

Similar to aliasing:

http://www.schorsch.com/de/kbase/glossary/images/aliasing.gif
 
Last edited by a moderator:
dst said:
I think what he's asking is, supposing that in the same way that pixels make up a monitor, Planck lengths of space make up our world, wouldn't a photon seem to suddenly skip down into the next Planck length instead of moving in a smooth curve a la macroscopic physics?

Similar to aliasing:

http://www.schorsch.com/de/kbase/glossary/images/aliasing.gif
[/URL]

That is exactly what I mean. Basically you explained it better then i could. But I guess the curved spacetime does make sense of it anyway. Thanks for the answer, I've been thinking about this all day.
 
Last edited by a moderator:
bassplayer142 said:
That is exactly what I mean. Basically you explained it better then i could. But I guess the curved spacetime does make sense of it anyway. Thanks for the answer, I've been thinking about this all day.

A photon whose wavelength was about the Planck length would have enormous energy - probably enough to start another big bang. The kinds of photons we deal with ( even gamma rays) have wavelengths which are gazillions* of times bigger that the Planck length.

* I don't know the actual number but about 10^20 should cover it ( with tip ).

A gravitating body needs to be very dense before photons are stopped from leaving by the field. On earth, photons escape easily but instead of slowing down they appear to stretch while escaping.
 
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