Mapping Space with Clocks: Deduce Distances/Observers w/ Constant Light Speed

  • Context: Graduate 
  • Thread starter Thread starter I_ponder
  • Start date Start date
  • Tags Tags
    Clocks Mapping Space
Click For Summary

Discussion Overview

The discussion revolves around the problem of deducing distances and the positions of observers using only clocks and the assumption of constant light speed. Participants explore the implications of having multiple observers and the necessary conditions for measuring distances based on time delays of light signals from distant events.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes that with only clocks, a single observer cannot measure distance, as they can only time events without additional information.
  • Another participant argues that if light signals are available, a single observer can measure distance using their clock, referencing RADAR as an example.
  • There is a discussion about the minimum number of observers needed to deduce distances, with one participant questioning how two observers can determine their separation or the distance to an event without additional information.
  • A later reply suggests that with four known events that are null separated, it is possible to formulate equations to solve for the position of an unknown event, emphasizing the need for synchronized clocks and known positions in a reference frame.
  • Participants highlight the importance of light signals in conjunction with clocks for determining distances and positions, referencing how GPS systems operate as an example.

Areas of Agreement / Disagreement

Participants express differing views on whether clocks alone can measure distance and the necessary conditions for doing so. There is no consensus on the minimum number of observers required or the specific methodology for deducing distances based solely on time delays.

Contextual Notes

Participants note the necessity of synchronizing clocks and knowing their positions in a reference frame, as well as the implications of acceleration on measurements, which remain unresolved in the discussion.

I_ponder
Messages
2
Reaction score
0
Suppose that we do not have any way to measure distance, but do have clocks. There are N observers, who can all see the distant events, say spaceships taking off and landing on far away planets. The question is: assuming the speed of light is constant, can we deduce the distance to the events and other observers based on differing delays? What is the minimum number of observers/observations required?

I know this is a general question, but I would be interested in a general solution, and any necessary preconditions.
 
Physics news on Phys.org
If you have clocks and light signals then you can measure distance.
 
I think you missed the point.

If I have 1 observer, he cannot measure distance just using a clock. All he can do is time events. That's not measuring distance.

If the there are 2 observers, and they both see the same events, then they can time events, and one observer can tell the other one what they saw as the delay in between them. But using that information how do they know how far apart they are? Or how far the event was? Perhaps one is accelerating? Perhaps they are both are? Perhaps they are tracking a single object that is accelerating?

How many observations do we need? How many observers?

Can anyone produce an algorithm?
 
DaleSpam said:
... light signals ...
I_ponder said:
...what they saw as the delay...
Seems like you are saying the same thing as DaleSpam.
 
I_ponder said:
If I have 1 observer, he cannot measure distance just using a clock
If he can use light signals in conjunction with his clock then he certainly can use his clock to measure distance. This is called RADAR
 
If you have one unknown event and four known events which are null separated (meaning that a light signal can go between the known events and the unknown event) then you can write four equations in four unknowns and solve for the time and position of the unknown event. The four events have to be known, otherwise you have more unknowns than equations.

So you would need more than just the clocks, they would need to be synchronized and you would need to know their positions in some reference frame. This is how GPS works. One of the very important parts of the GPS system is the radars which are used to make sure that we accurately know the positions of the GPS satellites. It is all just clocks and light signals. You cannot do it without the light signals, but with them it is possible to determine the time and location of an unknown event using four "observer clocks".
 

Similar threads

  • · Replies 34 ·
2
Replies
34
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 42 ·
2
Replies
42
Views
3K
  • · Replies 23 ·
Replies
23
Views
2K
  • · Replies 25 ·
Replies
25
Views
5K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 20 ·
Replies
20
Views
3K
  • · Replies 51 ·
2
Replies
51
Views
5K