Unit of Measurement: Arbitrary or Dependent on Physical Laws?

[MiltMeyers]

Great posts! Yes I am in error and thanks for nailing my foot to the floor. Mass will we find the higgs boson? I always liked the idea that the universe and the object are connected and when you have inertia you move the universe. Maybe the universe and the object trade higgs particles?

Back to gravity being due to warped space time(ST). Space time is warped or curved by an exspansion of ST and that would mix with mass warped ST and show up at low levels. So in an exspanding universe the curve would lower gravity but with an collapsing universe it would add to gravity, or do I have that turned around.

Junglist I agree there are some really smart people reading this forum.

 

[NYSportsguy]

Hi MiltMeyers and NYSportsguy, here's an easy way to think about why the pull of gravity corresponds to the mass of the object:

By this elementary reasoning it would defy common sense to expect a more massive object to accelerate faster than a less massive object. Linking individual hadrons together (chemically) does not cause any (significant) change in their individual inertias. It would be bizarre indeed if linking hadrons together caused them to each become more (or less) susceptible to gravitational force than the same number of hadrons that are unlinked.

Jon

JonMTKisco - That exactly what I said in my explanation above. It's the force that varies with variation in the masses being "pulled" on...the acceleration stays constant. I already know that but thanks for the more "Quantum" explanation.

 

[NYSportsguy]

The original statement to start this post was: "What if the universe does not expand, but matter condenses. This does not indicate whether space is expanding/fixed or anything, but just that matter is condensing. This could explain the observation that points in space are moving away from one another, as the distance between galaxies etc. would increase as the size of the galaxies decreases."

To Answer that my Reply Would Be: If matter were condensing it would still be the same amount of matter however volume would shrink. Since density = mass/volume all we would need to do it measure our own galaxy's density at a certain point in time and then say 500-1000 years later measure the density again. If we see it is increasing, we can say that it is because the volume has been decreasing due to the "condensing process" of matter and as a result the contraction theory would be correct.

However I don't believe scientists have found the density of individual galaxies to be increasing as time passes so there goes that theory.

 

[MiltMeyers]

NYsportsguy----Thats a good point about the fact the galaxys would decrease. I think the spin of the galaxy would hold the stars out in an orbit about the center but as you say the push would be to collapse the galaxy. That is why I said that the push would help gravity and the stars would spin as if there was dark matter out there holding the galaxy together. No I'll stick to what I understand and that is an exspanding universe.

 

[robheus]

I think this "dilemma" is just the ordinary issue of how to define a ruler. And that is just basic sanity, applicable anywhere, that your choice of ruler does not change anything. All physics stays the same (only the numbers/outcomes of your formula's change).
And if I'm not wrong, even a time dependent unit would not make a difference.

It is analogous to the choice of frame of reference.

So the whole issue is one which is solely based on choice of ruler, and there is no physics that change, so not testable by definition.

And same as that we choose for our frame of reference not the galactic center or andromeda but (for practical reasons) the solar system or earth, likewise we do not choose our length unit to be the distance between too far away galaxies, but some more practical unit.

 

[NYSportsguy]

But if we know that the density is not increasing for each individual galaxy (thus volume is not getting smaller as it should if matter were condensing) and yet the distance between galaxies continues to increase as measured by the redshift Doppler Effect on light wavelengths, then we can conclude that it is the universe that is expanding and not the galaxies themselves condensing with the universe staying static.

 

[robheus]

But if we know that the density is not increasing for each individual galaxy (thus volume is not getting smaller as it should if matter were condensing) and yet the distance between galaxies continues to increase as measured by the redshift Doppler Effect on light wavelengths, then we can conclude that it is the universe that is expanding and not the galaxies themselves condensing with the universe staying static.

The unit of measurement is arbitrary and does not depend on phsyical laws as I see it.
In general this is true. If we were to abandon the unit of length and replace it with a unit twice as large, nothing physical would change.
Now the case here is somewhat more complex, since we would replace the unit of measurement that is not a linear variant of the old unit but time dependent variant of the previous unit, but still I can not think of anything that would make a physical difference.
Just that some choices for your units are "better" in the sense that physical laws are easier to describe in them.

In the case you mention, about measuring the density, please note that changing your units of measurements does not have any impact on that, since you don't measure an ABSOLUTE density, but a RELATIVE one (since you compare this for example with the density of a Standard Kilogram), and both change in the exact same proportion due to the change of unit, so your measurements would result in the EXACT same result.
Simple logic.