Can Gravity and Acceleration Ever Equal the Speed of Light?

  • Context: Undergrad 
  • Thread starter Thread starter JonMcD
  • Start date Start date
Click For Summary

Discussion Overview

The discussion centers around the relationship between gravity, acceleration, and the speed of light, particularly in the context of Einstein's theories of relativity. Participants explore concepts related to gravitational effects on light, the nature of acceleration, and the implications of these ideas for understanding black holes.

Discussion Character

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

Main Points Raised

  • One participant questions whether gravity can reach the speed of light, suggesting that if acceleration cannot, gravity should also be limited in this way.
  • Another participant clarifies that Einstein did not state that gravity equals acceleration, emphasizing the distinction between acceleration and velocity, and suggesting that the original question reflects a misunderstanding of these concepts.
  • A third participant agrees with the clarification and explains that Einstein's equivalence principle means that a freely falling system cannot be distinguished from an inertial system, but notes that this holds locally.
  • A later reply points out that the equivalence principle only applies locally and that it is possible to distinguish between acceleration and gravity in non-point systems.

Areas of Agreement / Disagreement

Participants express differing interpretations of Einstein's principles and the relationship between gravity and acceleration. There is no consensus on the original question regarding gravity's ability to reach the speed of light, and the discussion remains unresolved.

Contextual Notes

Some limitations in understanding are noted, particularly regarding the definitions of acceleration and gravity, and the local versus global implications of the equivalence principle.

JonMcD
Messages
2
Reaction score
0
Hi, I'm very new to physics and I was just wondering if any of you might be able to awnser a question for me. Its probably a question only someone who doesn't know pretty much any physics would ask, so if you all could humor me I would appreciate it :) Oh and sorry if I posted this in the wrong section.

Ok here goes. I believe it was Einstein who said that gravity and accerleration are equal. Acceleration can not reach the speed of light (your mass would approach infinity?) so shouldn't it also be true that gravity can not reach the point where it's gravity (measured in acceleration) would equal the speed of light? And for light to be stopped or trapped by any kind of gravity, wouldn't the gravity have to be equal, in acceleration terms, to the speed of light? And yet isn't that exactly what a black hole does, or do black holes just affect light in a different way?

Sorry if the above seems a bit disjointed, I'm having an attack of insomnia and lack of sleep tends to make me a little less coherent then normal. Anyway thanks for bearing with me.
 
Physics news on Phys.org
OK...

first of all, Einstein did not ever say that gravity and acceleration are equal. While it is true that (in absence of air resistance) the gravitational field strength of a planet is equal to the acceleration of an object near that planet's surface, this is not the same as saying "gravity equals acceleration."

Second of all,Special Relaativity suggests that the velocity of an object can not reach the speed of light. Acceleration is not the same as velocity; acceleration is the rate of change in velocity (how quickly you change how fast you go, such as "zero to 60 mph in 10 seconds" means an acceleration of 6 mph/sec.

You are thinking some interesting thoughts, but what you suggest is unfortunately nonsensical because you don't have the definitions of these concepts entirely straightened out. Keep thinking new thoughts, but study Newtonian physics some more before taking on Einstein's relativity
 
Agree with the Chi Meson.

What you heard or read about "gravity equals acceleration" is Einstein's fundamental post of general relativity. I don't know much more about this subject yet, but here's what it actually means: a system free of gravitational forces which moves with constant acc. can't be distinguished of a inertial system in a grav. field of the same amount. In other words, you can't tell whether you sit in a rocket far from Earth that travels with acc. g or you sit in the same rocket standing still on earth.
 
Got it, thanks for clearing that up for me.
 
Originally posted by kuengb
a system free of gravitational forces which moves with constant acc. can't be distinguished of a inertial system in a grav. field of the same amount. In other words, you can't tell whether you sit in a rocket far from Earth that travels with acc. g or you sit in the same rocket standing still on earth.

This only holds localy.
As long as the rocket is not just a point it's possible to distinguish between acceleration and gravity.
 
Last edited:

Similar threads

High School Speed of light and this Accelerating Rocket scenario
  • · Replies 45 ·
2
Replies
45
Views
5K
Undergrad Can Gravity Escape a Black Hole?
  • · Replies 21 ·
Replies
21
Views
3K
Undergrad Is Erik's Paradox Challenging Our Understanding of Gravity and Light Speed?
  • · Replies 18 ·
Replies
18
Views
2K
Undergrad Gravity at Schwarzschild Radius of a Black Hole
  • · Replies 17 ·
Replies
17
Views
4K
Undergrad Can light be reflected in a black hole?
  • · Replies 22 ·
Replies
22
Views
2K
Undergrad A question about the speed of light and electromagnetism
  • · Replies 51 ·
2
Replies
51
Views
5K
Undergrad Is Measuring the One-Way Speed of Light Possible Near a Black Hole?
  • · Replies 10 ·
Replies
10
Views
2K
Undergrad Light speed independent of source
  • · Replies 22 ·
Replies
22
Views
2K
Undergrad Euclidean geometry and gravity
  • · Replies 169 ·
6
Replies
169
Views
11K
Undergrad Looking closely at the descent into a black hole
  • · Replies 51 ·
2
Replies
51
Views
3K