How Does a Black Hole Attract Light?

  • Context: Undergrad 
  • Thread starter Thread starter Manu Vincent
  • Start date Start date
  • Tags Tags
    Black hole Hole Light
Click For Summary

Discussion Overview

The discussion revolves around the nature of black holes and their ability to attract light, focusing on the gravitational effects of black holes and the curvature of spacetime. Participants explore theoretical implications, analogies, and the distinction between mass and gravitational effects on light.

Discussion Character

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

Main Points Raised

  • Some participants assert that black holes attract light due to their high gravitational force, despite light being massless.
  • One participant explains that a gravitational source curves the spacetime through which light travels, suggesting that light follows a straight path in this curved spacetime.
  • Another participant questions whether black holes only curve spacetime and what other properties they might possess.
  • A participant introduces the concept of path curvature versus sectional curvature, discussing the implications for light's behavior in a gravitational field.
  • There is mention of analogs of black holes, including acoustic metrics, and references to external resources for further exploration of these ideas.
  • A participant suggests using a Newtonian approximation to consider relativistic mass in the context of light and gravity.
  • One participant humorously addresses the complexity of the explanations provided, indicating a struggle to fully grasp the technical details.

Areas of Agreement / Disagreement

Participants express varying viewpoints on the nature of black holes and their interaction with light, with no clear consensus reached. The discussion includes both agreement on certain principles and ongoing questions about the implications of those principles.

Contextual Notes

Participants reference complex concepts such as spacetime curvature, null geodesics, and the distinction between different types of curvature, indicating a nuanced discussion with unresolved mathematical and conceptual elements.

Who May Find This Useful

This discussion may be of interest to those exploring gravitational physics, the nature of light in strong gravitational fields, and the theoretical implications of black holes.

Manu Vincent
Messages
2
Reaction score
0
Hi all,
We know that the black hole is able to pull every thing that get near to it, even light because of its high gravitational force. But, we know that light is mass less. Then how will black hole attract light?
 
Physics news on Phys.org
A gravitational source doesn't directly act upon the light. Rather, it curves the space-time that the light is traveling through. The light 'thinks' that it's still going in a straight line.
 
I agree with Danger, but does it only curves space-time?
 
little physicis said:
I agree with Danger, but does it only curves space-time?
Gravitation = Spacetime curvature.
 
little physicis said:
I agree with Danger, but does it only curves space-time?

Well, what else do you think a massive object should "curve", in addition to spacetime?

Don't confuse path curvature with sectional curvature. Path curvature is the magnitude of the acceleration vector of a curve, and has relativistic units of reciprocal length. The Riemann curvature tensor, which measures the curvature of spacetime, has components which are sectional curvatures, and they have relativistic units of reciprocal area (so do mass and energy density).

As Danger said, in gtr, in the geometric optics approximation, a laser pulse has a world line which is a null geodesic of the spacetime (a Lorentzian manifold), so its acceleration vector and thus its path curvature vanishes identically. This does not contradict the notion of "light bending", just implies that "light bending" means something a little different from what you might think at first, er, sight :wink:
 
Last edited:
let's (curve) this subject a bit, does the black hole only could do the curve thing? and is it posibel to get ((some thing)) that would have the same properities that the blak hole has??
 
:biggrin: just thinking loud:biggrin:
 
Acoustic and other analogs of black holes

little physicis said:
let's (curve) this subject a bit, does the black hole only could do the curve thing? and is it posibel to get ((some thing)) that would have the same properities that the blak hole has??

A not terribly successful attempt to explain in nontechnical terms a currently popular idea in gravitation physics:
http://en.wikipedia.org/w/index.php?title=Acoustic_metric&oldid=26629648
An excellent and authoritative technical survey:
http://relativity.livingreviews.org/Articles/lrr-2005-12/index.html
 
Last edited by a moderator:
If you were going to take a Newtonian approximation (treating gravity as a force), I think it's fair to say you'd use relativistic mass (which is non-zero for light) rather than rest mass.
 
  • #10
LOOK AT ENCARTA'S BRILLIANT GR ANALOGY! It can easily explain this problem...
 
  • #11
Chris Hillman said:
As Danger said, in gtr, in the geometric optics approximation, a laser pulse has a world line which is a null geodesic of the spacetime (a Lorentzian manifold), so its acceleration vector and thus its path curvature vanishes identically. This does not contradict the notion of "light bending", just implies that "light bending" means something a little different from what you might think at first, er, sight :wink:

So you're the one who's been screwing with my reputation. :-p
You start with 'As Danger said', and proceed with an explanation that I can't begin to understand after reading it a dozen times. Now I know why I keep getting PM's from people who think that I know what I'm talking about. Stop that! :biggrin:
 

Similar threads

  • · Replies 22 ·
Replies
22
Views
2K
  • · Replies 31 ·
2
Replies
31
Views
2K
  • · Replies 40 ·
2
Replies
40
Views
4K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 51 ·
2
Replies
51
Views
2K
  • · Replies 20 ·
Replies
20
Views
3K
  • · Replies 22 ·
Replies
22
Views
2K
  • · Replies 62 ·
3
Replies
62
Views
9K
  • · Replies 4 ·
Replies
4
Views
2K