Understanding Time Dilation and Light Sources in Relation to Mass

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Discussion Overview

The discussion revolves around the concept of time dilation in relation to mass and light, exploring how mass affects the perception of time and the speed of light from different reference frames. Participants examine the implications of relativity, the behavior of light near massive objects, and the fundamental nature of light's velocity.

Discussion Character

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

Main Points Raised

  • Some participants propose that massive objects slow down time relative to an outside observer, questioning why light is not similarly affected.
  • Others argue that while light appears to travel slower to a distant observer due to time dilation, a local observer measures light at the speed of c.
  • A participant highlights the core idea of relativity that the speed of light remains constant in a vacuum, prompting questions about the implications of this constancy in different gravitational contexts.
  • There is a discussion about the relationship between speed, frequency, and wavelength, with some suggesting that if time slows and frequency decreases, wavelength must increase to maintain the speed of light.
  • Concerns are raised about the clarity of explanations regarding light speed observations, emphasizing the importance of context in understanding measurements from different reference frames.
  • Participants express curiosity about the fundamental nature of light's constant velocity and the reasons behind gravitational effects on space and time.

Areas of Agreement / Disagreement

Participants generally express differing views on the implications of time dilation and the behavior of light near massive objects. There is no consensus on the interpretations of these phenomena, and the discussion remains unresolved.

Contextual Notes

Some claims rely on specific assumptions about reference frames and the nature of light, which may not be universally accepted. The discussion includes unresolved questions about the fundamental principles governing light and gravity.

Denton
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Sources of great mass slow time down relative to an outside observer, so why is it that light itself is not slowed down, not in velocity but simply due to the fact that time has slowed down near the mass?
 
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good question, no good answer.
One of the many great mysteries of physics! Why should mass curve space??
You could say that atomic structure requires stable EM fields...but then why did they evolve that way? either "somebody" planned it just right or there are an infinite number of combinations...and only those universes which "work" are able to evolve...and perhaps give birth to others...
 
Denton said:
Sources of great mass slow time down relative to an outside observer, so why is it that light itself is not slowed down,
It is!
Denton said:
not in velocity but simply due to the fact that time has slowed down near the mass?
Exactly like this. The distant observer will measure the light near the mass to travel at less than c, using his own fast clock. It will appear "slowed down" to him. But the local observer near the mass with a slow clock will measure the light passing him at c.
 
A.T. said:
It is!

Exactly like this. The distant observer will measure the light near the mass to travel at less than c, using his own fast clock. It will appear "slowed down" to him. But the local observer near the mass with a slow clock will measure the light passing him at c.
Is that right? I thought one of the core ideas behind relativity was the constancy of the speed of light, meaning that no matter where you are at in the universe, you would always measure the speed of light (in a vacuum) to be 3x10^8 meters/second. Is there something I've misunderstood?
 
Anything wrong with this handwaving?

c=f.l (speed = frequency.wavelength)

Time is related to frequency. If time slows, frequency decreases, but if wavelength also increases, speed can stay the same.
 
LucasJ said:
Is that right? I thought one of the core ideas behind relativity was the constancy of the speed of light, meaning that no matter where you are at in the universe, you would always measure the speed of light (in a vacuum) to be 3x10^8 meters/second
That's correct for light near you. But the OP is asking about an outside observer measuring the speed of light in a gravity well.

atyy said:
Anything wrong with this handwaving?

c=f.l (speed = frequency.wavelength)

Time is related to frequency. If time slows, frequency decreases, but if wavelength also increases, speed can stay the same.
Not only frequency is affected. If you send a light signal from outer space to a mirror stationary to you in a gravity well, it will return with the same frequency. But it still will need longer then if there was no gravity. So it will appear to you, that it was slowed down.
 
Last edited:
I disagree witht he first part of post #3...it's potentially rather confusing...but it's dependent on context...part two properly explains the way to think about lightspeed observations: local observers see light at "c"; distant observers see things differently depending on their reference frame.
 
Anything wrong with this handwaving?

c=f.l (speed = frequency.wavelength)

Time is related to frequency. If time slows, frequency decreases, but if wavelength also increases, speed can stay the same.

Ah yes, speed remains constant and its constituents change to stabilise it. Thus we see red shifting occurring at high gravitational potentials.

Then comes to the other question. What is so special about the velocity of light that it must remain constant, and that its frequencies and wavelengths are but insignificant.
 
Then comes to the other question. What is so special about the velocity of light that it must remain constant, and that its frequencies and wavelengths are but insignificant.

Exactly! and also enigmatic: why should gravitational potential (a) curve space and (b) change time?? We have descriptions to explain what happens, but not WHY!...did it have to be this way?? Might other universes have different relationships??
 

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