Which Watch Will Have Slower Time: Object 1 or Object 2?

Click For Summary

Discussion Overview

The discussion revolves around the question of which watch will show slower time between two objects, one moving (Object 1) and one static (Object 2), particularly in the context of special relativity and time dilation. Participants explore various scenarios, assumptions, and implications of relative motion and reference frames.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that without a reference object, it is impossible to determine which object is moving, leading to multiple scenarios based on the position of a hypothetical reference object.
  • Others argue that if Object 1 is moving at the speed of light, the question becomes meaningless since nothing can move at that speed according to relativity.
  • A participant suggests that if Object 1 is moving close to the speed of light, time dilation effects can be discussed, and they provide equations for time experienced by both objects.
  • Some participants emphasize that different observers will measure the clocks of the other as ticking slower, depending on their relative motion.
  • There is a discussion about the relativity of simultaneity, where participants note that observers in different reference frames will disagree on what "at the same time" means.
  • A later reply questions the assumptions made about the speeds of the objects and the need for more information about the reference frame to determine time dilation effects accurately.
  • One participant proposes that both scenarios of time dilation cannot be true simultaneously, suggesting a need for deeper consideration of the implications of special relativity.

Areas of Agreement / Disagreement

Participants generally disagree on the implications of the scenarios presented, particularly regarding the validity of the original question and the assumptions made about the speeds of the objects. The discussion remains unresolved, with multiple competing views on how to approach the problem.

Contextual Notes

Limitations include the lack of clarity on the speeds of the objects in the reference frame and the assumptions about simultaneity, which are critical to understanding time dilation in special relativity.

  • #31
Sandip Patel said:
Edwin Hubble said universe is expanding at the speed faster than light. Galaxy at 14 billion light years are going far away from Earth at speed of light. Some galaxies farther than 14 billion light years cannot be seen by human as light will not reach to earth.

Why it will happen if you all say its only "C" my above question?

View attachment 234648

References:
https://www.space.com/33306-how-does-the-universe-expand-faster-than-light.html

https://www.loc.gov/rr/scitech/mysteries/universe.html

https://phys.org/news/2015-02-fast-universe.html

Is this thread about time dilation or the expanding universe?

One thing at a time, please!
 
  • Like
Likes   Reactions: Sandip Patel and DaveC426913
Physics news on Phys.org
  • #32
Sandip Patel said:
Why it will happen if you all say its only "C" my above question?
The second postulate states that the speed of light in vacuum is c in any inertial frame. There is no inertial frame that contains both the Earth and a galaxy 14 billion ly away.

The equivalent statement in GR is that light always travels on null geodesics. In inertial frames this statement reduces to the usual second postulate, but in non inertial frames it remains valid.

I strongly recommend that you stick with SR for now
 
  • Like
Likes   Reactions: Sandip Patel and Ibix
  • #33
Sandip Patel said:
Why it will happen if you all say its only "C" my above question?
Because the concept of velocity of a distant object is a rather ambiguous one in curved spacetime. Invariably, you will find that the velocity of light as measured by a local observer is c. Distant observers can measure more or less any value, but it has no physical significance.

You are currently struggling with special relativity. You need to get that understood before you try seriously grappling with general relativity.
 
  • Like
Likes   Reactions: Sandip Patel and Dale
  • #34
Sandip Patel said:
Edwin Hubble said universe is expanding at the speed faster than light.
To add to what others have already pointed out, you are confusing recession velocity, which is unlimited because nothing is "moving" in the sense you think it is, with actual proper motion which is where the limit of c applies. I agree w/ Dale. Let's drop consideration of the expanding universe (GR) since you apparently haven't studied it yet, and stick with special relativity.

EDIT: I see ibix beat me to it.
 
  • Like
Likes   Reactions: David Lewis, Sandip Patel, nitsuj and 2 others
  • #35
Sandip Patel said:
time dilatation happen, which watch will have slowed down time. Please help me understand the practical result if we have such case.

The practical result is called differential aging. To be specific, it's not really correct to say "slowed down", it's accurate to say one clock measured more time than the other. Some conceptualize this as a path; a distance measured.
 
  • Like
Likes   Reactions: Sandip Patel
  • #36
Sandip Patel said:
Edwin Hubble said universe is expanding at the speed faster than light. Galaxy at 14 billion light years are going far away from Earth at speed of light. Some galaxies farther than 14 billion light years cannot be seen by human as light will not reach to earth.

Why it will happen if you all say its only "C" my above question?

The universe is allowed too! That is spacetime "itself" that, cumulatively over vast distances sum to recession velocities greater than c.

The stuff "within" obeys c.

imo it's a fair point the op raised regarding recession velocity, and seems a common consideration when learning about c. The distinction is vast & easily understood and "important".
 
Last edited:
  • Like
Likes   Reactions: Sandip Patel
  • #37
nitsuj said:
The practical result is called differential aging.
No - differential aging is what you get in a frame-invariant experiment like the twin paradox, where two clocks meet up, part, and meet up again. Time dilation is an effect between two inertial frames where clocks can only meet at most once.

While you can view it in terms of the same "interval" based analysis as is often used for the twin paradox, you need more than just distance. The two worldlines are at an angle to each other and their own planes of "now" are orthogonal to the lines. Thus they differ over what counts as "the same time" except when they meet and the distance from the meeting point "now" differs.
 
  • Like
Likes   Reactions: Sandip Patel
  • #38
Ibix said:
No - differential aging is what you get in a frame-invariant experiment like the twin paradox, where two clocks meet up, part, and meet up again. Time dilation is an effect between two inertial frames where clocks can only meet at most once.

Was presuming the OP was meaning the clocks are compared (at rest to each other) after time dilation, worded as "practical result".

Why must the clocks meet up at the start? I appreciate they need to be synchronized, but don't follow why they must "meet up" at the start for it to be called differential aging.

Err..never mind, I see it now. You said it in the first sentence, frame invariant scenario.
 
  • Like
Likes   Reactions: Sandip Patel

Similar threads

Undergrad Time Dilation: Gravitational & Velocity Effects Explained
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad Non-Inertial Relativistic Dynamics
  • · Replies 18 ·
Replies
18
Views
2K
Undergrad Question about geometrical engineering (placeholder name)
  • · Replies 32 ·
2
Replies
32
Views
2K
High School Does Relativity Impact Gravity's Influence on Fast-Moving Objects?
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Teaching Minkowski diagrams effectively
  • · Replies 15 ·
Replies
15
Views
3K
Undergrad What Happens When an Object Accelerating Away from a Black Hole Stops?
  • · Replies 35 ·
2
Replies
35
Views
4K
Undergrad Special Relativity: 3 Objects, Momentum & Time Dilation
  • · Replies 4 ·
Replies
4
Views
1K
High School Mechanics behind curved time causing gravitation/geodesics
  • · Replies 27 ·
Replies
27
Views
7K
High School Prove the velocity of a moving object is absolute in one IRF?
  • · Replies 22 ·
Replies
22
Views
2K
High School Why does length contraction occur and how does it relate to time dilation?
  • · Replies 63 ·
3
Replies
63
Views
6K