Why does time stop in the event horizon of a blackhole?

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Discussion Overview

The discussion centers on the nature of time at the event horizon of a black hole, particularly whether time stops or slows down, and how this phenomenon is perceived from different reference frames. The conversation touches on theoretical implications from General Relativity, as well as interpretations of time dilation and gravitational redshift.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why time appears to stop or slow down at the event horizon of a black hole.
  • Another participant notes that the perception of time depends on the observer's reference frame, stating that an object falling into a black hole experiences no effect on time, while a distant observer sees it as slowing down.
  • A participant references Leonard Susskind's lectures as a resource for understanding the mathematical aspects of the topic.
  • One participant suggests that time does not actually decrease but appears slowed down due to redshift or blueshift, seeking clarification on this point.
  • Another participant asserts that time dilation is a real effect and not merely a result of redshift, emphasizing the reality of gravitational time dilation and its connection to gravitational redshift.
  • A participant elaborates on the relationship between gravitational time dilation and gravitational redshift, arguing that both phenomena are real and interconnected.
  • There is a discussion about the experimental testing of gravitational effects through the exchange of light signals between different reference points.

Areas of Agreement / Disagreement

Participants express differing views on the nature of time at the event horizon, particularly regarding the distinction between appearance and reality in the context of time dilation and redshift. No consensus is reached on these interpretations.

Contextual Notes

Participants reference concepts from General Relativity and the implications of gravitational effects, but there are unresolved assumptions regarding the definitions and interpretations of time dilation and redshift.

Manraj singh
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Why does time stop in the event horizon of a black hole? Or at least slow down, from what i know.
 
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It depends on the reference frame. Something falling in experiences no effect on time. However a distant observer would see the object as slowing down and never quite falling in.

The explnation is in the equations of General Relativity. (I am no expert).
 
leonard susskind describes it pretty good on youtube classic mechanics lectures from stanford university really learned a lot from his lecture heavy into math if you ask me but he says it elementary math
 
Mr Marcus, the link given by you helped a lot. Please correct me if I am wrong: time does not actually decrease, but it appears to be slowed down due to red shift or blue shift.Sent from my iPad using Physics Forums
 
Manraj singh said:
Mr Marcus, the link given by you helped a lot. Please correct me if I am wrong: time does not actually decrease, but it appears to be slowed down due to red shift or blue shift.Sent from my iPad using Physics Forums

Time dilation really does occur, it's not just a result of red shift.
 
Manraj singh said:
Mr Marcus, the link given by you helped a lot. Please correct me if I am wrong: time does not actually decrease, but it appears to be slowed down due to red shift or blue shift.
...

I think people can have different perspectives on appearance vs. reality, Manraj.

Personally I consider gravitational time dilation to be absolutely real! And I consider it to be the same phenomenon as gravitational redshift.

Deeper down clocks run slower, the evolution of physical states is slower, the atoms in the downstairs laser vibrate slower, so the light it makes is redder---all from the standpoint of the guy upstairs.

The gravitational time dilation is what CAUSES the gravitational redshift. So both are actually real. That is just how I see it. Other people may have different ways to understand it.

I can see no other explanation for the gravitational redshift. Can you?

I think the way they experimentally TEST these gravitational effects is by sending light (or other electromagnetic signals) back and forth between "upstairs" and "downstairs" atomic clocks and other devices.
 

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