The Naked Scientists

The Naked Scientists Forum

Author Topic: Is gravity very weak because its been stretched out?  (Read 1161 times)

Offline acecharly

  • Sr. Member
  • ****
  • Posts: 171
    • View Profile
If such as matter there was so much to start with was gravity the same?

How accurately can gravity be measured? Is it to many decimal places?

If we could measure it accurately enough would we see it getting weaker as the universe expands and also be able to measure the speed that it is expanding?


 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 249 times
    • View Profile
Re: Is gravity very weak because its been stretched out?
« Reply #1 on: 30/03/2014 04:04:17 »
"Gravity" can mean many different things in different contexts:
  • Gravity waves are the propagation of disturbances in the gravitational field. The announcement this month about the discovery of gravitational waves from the big bang showed that gravitational waves were very strong in the early universe. These "primordial" gravity waves would now be very stretched out by the expansion of the universe. Although they were very strong in the past, they are so weak today that astronomers do not expect to ever observe them directly.
  • In the next decade, astronomers are hoping to detect gravity waves from colliding black holes in today's universe. Because gravity waves propagate at the speed of light, any relative motion will result in a red shift or blue shift. However, this effect will be very slight if the originating black holes are in our galaxy.
  • I think the astronomers will be very happy about detecting any current-day black holes without initially worrying about measuring their Doppler shift (or detecting black holes in other galaxies, where the Doppler shift will be greater).
  • Massive objects like stars & galaxies create a "gravitational well". As the universe expands, the average depth of the gravitational well will reduce (but it will stay roughly the same for individual stars and galaxies, as it is the space between the galaxies that is stretching out).
  • Gravity is the acceleration of a mass near a star or a planet. If the mass is sitting on the surface of the Earth, we say that this force is its weight. If the mass of the Earth remains the same, the weight of an object should remain the same, despite the expansion of the universe.
 

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
Re: Is gravity very weak because its been stretched out?
« Reply #2 on: 30/03/2014 05:30:15 »
Quote from: acecharly
If such as matter there was so much to start with was gravity the same?
Please restate that sentence. I can't make head or tails out of it.

Quote from: acecharly
How accurately can gravity be measured? Is it to many decimal places?
It'd be best if you simply did a search on the internet for the precision of various gravimeters and gradiometers. E.g. see http://www.scintrexltd.com/brochure/MgL_FG5.pdf

Quote from: acecharly
If we could measure it accurately enough would we see it getting weaker as the universe expands and also be able to measure the speed that it is expanding?
No.
 

Offline zunimtn

  • First timers
  • *
  • Posts: 9
    • View Profile
Re: Is gravity very weak because its been stretched out?
« Reply #3 on: 07/04/2014 00:02:26 »
My (for what it's worth) sense of the gravity wave aqnouncement thing was that they  thought (and nothing is definite yet) they were maybe seeing gravity wave effects from the inflation event.  That would be because at inflation, it's thought the universe expanded its size enormously in a very very very brief moment of time, which could produce some big energy in the gravitational field (that is, waves).  Like an earthquake causing a tsunami.

So I wouldn't say gravity has been "stretched out".  The strength of gravity depends only on mass.  All masses contribute to the variations of gravity gradients throughout the universe.  And while I can't say the strength of the gravitational force is lower than the other forces BECAUSE it would mess with their effectiveness in forming the complexities in the universe (like us) if it were stronger,  I'd say it would do just that.

 

The Naked Scientists Forum

Re: Is gravity very weak because its been stretched out?
« Reply #3 on: 07/04/2014 00:02:26 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums