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Author Topic: Is gravity getting weaker?  (Read 3717 times)

Offline MikeS

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Is gravity getting weaker?
« on: 28/11/2011 10:17:21 »
The Universe contains a finite amount of matter (and energy) by definition.
Matter (and energy) create space-time curvature that we call gravity.
The Universe is expanding.
The gravitational 'field' (for lack of a better term) has a certain density per unit volume.
If the Universe is expanding then this density must be decreasing.
Gravity dilates time. (The greater the gravity, the more time dilates).
Therefore as gravity weakens per unit volume of space then time contracts. 
In other words clocks run faster now than they did in the past.
What is wrong with this argument?


 

Offline imatfaal

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Is gravity getting weaker?
« Reply #1 on: 28/11/2011 11:59:49 »
The Universe contains a finite amount of matter (and energy) by definition.
  which definition. we do not know if the universe is infinite or finite let alone the energy content.

Quote
Matter (and energy) create space-time curvature that we call gravity.
The Universe is expanding
The gravitational 'field' (for lack of a better term) has a certain density per unit volume..
If the Universe is expanding then this density must be decreasing.
Not necessarily - the energy density of empty space remains constant   
Quote
Gravity dilates time. (The greater the gravity, the more time dilates).
  Again - not quite.  Differences in gravitational potential dilate time
Quote
Therefore as gravity weakens per unit volume of space then time contracts. 
Locally there is never any time dilation - it is only when viewed from another frame with a different gravitational potential.
Quote
In other words clocks run faster now than they did in the past.
What is wrong with this argument?
Clocks in the local frame run the same speed they did in the past and will in the future - when viewed from an alternate ifor they will be affected as they were in the past and future
 

Offline Gordian Knot

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Is gravity getting weaker?
« Reply #2 on: 28/11/2011 18:19:27 »
From my extremely uninformed opinion, what I understand is that gravity IS getting weaker. The force pulling everything apart is now the dominant force in the Universe. If that force, the supposed Dark Energy, is gaining strength, then gravity is losing pull (pun intended).

At least this is the conclusion I have come to understand from the limited knowledge I have.
 

Offline MikeS

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Is gravity getting weaker?
« Reply #3 on: 28/11/2011 19:43:24 »
The Universe contains a finite amount of matter (and energy) by definition.
  which definition. we do not know if the universe is infinite or finite let alone the energy content.

Quote
Matter (and energy) create space-time curvature that we call gravity.
The Universe is expanding
The gravitational 'field' (for lack of a better term) has a certain density per unit volume..
If the Universe is expanding then this density must be decreasing.
Not necessarily - the energy density of empty space remains constant  
Quote
Gravity dilates time. (The greater the gravity, the more time dilates).
  Again - not quite.  Differences in gravitational potential dilate time
Quote
Therefore as gravity weakens per unit volume of space then time contracts. 
Locally there is never any time dilation - it is only when viewed from another frame with a different gravitational potential.
Quote
In other words clocks run faster now than they did in the past.
What is wrong with this argument?
Clocks in the local frame run the same speed they did in the past and will in the future - when viewed from an alternate ifor they will be affected as they were in the past and future

Ok lets assume the Universe to be finite.  In which case its energy/mass content is finite.
I assume you are talking about the energy to create virtual particles?  But this does not alter anything, forget energy just think of mass.  The mass per unit volume is decreasing.
Ok perhaps I could have phrased it better but the same thing.
True but I am not talking about local time but the average of all local time(s) in the Universe.
Again as previously mentioned, I am not talking about clocks in the local time frame but an average of all clocks in the Universe.  Universal time if you like, not local time.
 

Offline imatfaal

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Is gravity getting weaker?
« Reply #4 on: 01/12/2011 13:46:35 »
You cannot forget energy. 
It is not the same thing.
There is no universal time - you either measure within your LIF (in which case time is undilated) or you measure in a different LIF in which case time is dilated.  There is no correct, absolute, universal, godlike time or LIF from which to observe it
 

Offline Nizzle

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Is gravity getting weaker?
« Reply #5 on: 01/12/2011 13:55:37 »
If everything in the universe with mass is moving further apart, then the gravitational force is indeed getting weaker no?

F=G×((m1.m2)÷r2) with r increasing, therefore F decreasing
 

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Is gravity getting weaker?
« Reply #5 on: 01/12/2011 13:55:37 »

 

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