14 minutes ago, swansont said:

clocks measure time, they are not time itself

Clocks are made from materials constantly effected by gravity and other fundamental interactions.. in other words, clocks aren't immortals.

4 hours ago, tylers100 said:

I don't know for fact, but I imagine some clocks would be surely heavier in some zones affected by different heights (e.g. gravity) and materials made.

A clock, like anything else, has lower mass when lower in a gravitational potential well than when above. The work done lifting the clock (or whatever) increases the mass of the clock. An atom in an excited state will have a greater mass than the same atom in the ground state. This difference in mass will have the same proportion to the mass of the atom regardless of where the atom is in the gravitational potential. Therefore, the energy of the photon emitted will be lower for the atom that is lower in the gravitational potential well and thus will be gravitationally redshifted. But it is gravitational redshift as the primary phenomenon that determines that mass is lower when lower in a gravitational potential well.

However, it is important to note that these differences in mass are measured from the same location. Measurements performed local to the clock (or whatever) will not indicate any differences, as required by the principle of relativity.

Edited December 17Dec 17 by KJW

13 hours ago, KJW said:

A clock, like anything else, has lower mass when lower in a gravitational potential well than when above. The work done lifting the clock (or whatever) increases the mass of the clock

Is that correct? The system earth-clock will have bigger mass, provided the energy for lifting the clock will come from a source outside the earth-clock sytem. No?

Other than the fact that I mentioned 'heavier' clocks in jest as a response to a post about time 'density', it see,s to me that a clock at a higher gravitational potential would have a higher potential energy than the same clock at a lower level in the well.
Its intrinsic/invariant/rest mass would be the same to all observers, but, energy being frame dependent, an external observer would measure a different total energy than an observer holding the clock.

Now, the interesting part that references back to the OP, is that a lot of our measuring equipment is also frame dependent, so whatever we measure by comparison in one frame, tends to be different from the measurement made by comparison to the instruments in another frame.
Yet invariant measurements are the same across all frames, so can they be said to be made by comparison ?

15 hours ago, tylers100 said:

Clocks are made from materials constantly effected by gravity and other fundamental interactions.. in other words, clocks aren't immortals.

You’re not making a compelling (i.e. physics-based) connection between these ideas, that the density of a clock somehow matters to the passage of time. That would mean the clock somehow affects time. How does time “know” that an item is a clock?

36 minutes ago, MigL said:

whatever we measure by comparison in one frame, tends to be different from the measurement made by comparison to the instruments in another frame.

Yet invariant measurements are the same across all frames, so can they be said to be made by comparison ?

Yes, since no matter the frames you are still, as you acknowledge, doing a comparison.

Suppose we have a mechanical clock with an observer at its centre.

The clock has symettrically spread moving components of mass comprising the mechanism.

Suppose those components are all moving away from the centre(a gravity well) at the same speed and that the clock as a whole continues to " tell the time".

As they move further out from the centre does the time as "told by the clock" seem to move more or less quickly to the observer at its centre-or the same?

1 hour ago, geordief said:

As they move further out from the centre does the time as "told by the clock" seem to move more or less quickly to the observer at its centre-or the same?

Exactly the same to the observer as he is at the same depth in the gravitational well.
It is termed 'proper time'.
Observers at other depths in the gravity well will see differing time.
( this is easier visualized with a light clock or signal )

On 12/12/2025 at 12:47 PM, swansont said:

  On 12/12/2025 at 12:00 PM, studiot said:

An 'absolute measurement' that MigL did not mention is 'count' : There is a count of two atoms of hydrogen in a water molecule and one atom of oxygen.

On 12/12/2025 at 12:47 PM, swansont said:

Yes. That’s a special category, and while you can have counting errors, you’re not really comparing it to anything.

I realize I'm a bit late on this conversation but isn't "count" being compared to nothing (i.e. zero)?

7 hours ago, npts2020 said:

I realize I'm a bit late on this conversation but isn't "count" being compared to nothing (i.e. zero)?

Intriguing comment. +1

It is not conventional, but I suppose since one way to generate the natural number system is from 'nothing' , that is the empty set, a case could be made for this.

However the empty set is not the number zero and any placement of zero in a number system causes controversy as it fits some applications of that number system but not others.

37 minutes ago, studiot said:

Intriguing comment. +1

It is not conventional, but I suppose since one way to generate the natural number system is from 'nothing' , that is the empty set, a case could be made for this.

However the empty set is not the number zero and any placement of zero in a number system causes controversy as it fits some applications of that number system but not others.

Sure, but in reality zero isn't quite the same as nothing in maths, just the best way we have of describing and using a null quantity for comparison, according to my understanding of it.

2 hours ago, npts2020 said:

Sure, but in reality zero isn't quite the same as nothing in maths, just the best way we have of describing and using a null quantity for comparison, according to my understanding of it.

I don't think you quite mean this so perhaps youd like to elaborate a bit about what you really mean.