Register to reply 
Isn't space expansion expectable? 
Share this thread: 
#1
Aug2605, 03:42 PM

P: n/a

Since Einstein showed that space and time are in fact entwined as a single entity spacetime, it makes me wonder if it's not just natural that we see space expanding with time.
As we examine spacetime forward in time (looking at regions where "the quantity of seconds" is increased regions where time has expanded), it may only be natural that we find also that "the quantity of meters" is also increased space has expanded as well ???? I know I'm wrong, because I know our physical theories allow scenarios where even when time continues to increase space shrinks, but I'd like someone to explain why the type of entanglement between space and time does not have anything to do with both increasing or decreasing together. And now that we talk about expansion, an even more silly question: Has anybody played with the hypotesis that from a relative perspective, it could be that instead of space expanding, matter and energy could be shrinking into a fixed size space? 


#2
Aug2705, 12:02 PM

Sci Advisor
PF Gold
P: 3,273

Garth 


#3
Aug2705, 12:13 PM

P: n/a




#4
Aug2705, 01:48 PM

Sci Advisor
PF Gold
P: 3,273

Isn't space expansion expectable?
[QUOTE=Gerinski]
In fact in the standard theory of cosmology spacetime is shaped by gravity, determined by the amount and distribution of the matter and energy within the universe, according to Einstein's GR field equation. I hope this helps, Garth 


#5
Aug2705, 09:18 PM

Sci Advisor
PF Gold
P: 9,384

Einstein made the case for a universe that must either expand, or contract. There is no stable, static solution to the field equations. Einstein was very surprised by this result and hand inserted the famous 'cosmological constant' [CC] to explain why the universe was not collapsing. Of course, being a pretty bright fellow, he was quick to realize this was like trying to balance a pencil on its point and expecting it to stay put. He recanted CC, calling it his 'greatest blunder', as soon as Hubble revealed the actual direction the universe is taking. Ironically, his retraction of CC now appears to be his 'greatest blunder'.



#6
Aug2705, 09:50 PM

P: 50

Perhaps the increasing expansion of the universe is simply the result of time speeding up.
As the mass of the universe becomes more spread out, wouldn't time speed up since the gravity of the universe is more spread out? 


#7
Aug2705, 11:17 PM

P: 193

If the expansion of space is accelerating wouldn't time be slowing down?



#8
Aug2805, 08:15 AM

P: 50

Maybe it isn't accelerating, Maybe it just appears to be because time is speeding up.



#9
Aug2805, 08:47 AM

Sci Advisor
PF Gold
P: 3,273

When statements like this are made you have to ask yourself: "How do you measure it?" The only way statements about time speeding up or slowing down make sense is when one clock is compared to another. The two famous examples are the time dilation observed by a stationary observer with a clock observing a fast moving (relative to her) clock; and the second is when an observer with a clock far away from a gravitating object observes a second clock deep down within the gravitational potential well. In both cases you have to think about how the observation itself, the exchange of photons, is made from one clock to the other. The third example that you can ponder over is the time dilation implicit in cosmological (Hubble) red shift. Events seen at the "far side of the universe", i.e. at high cosmological red shift, are observed to happen more slowly than those nearby. Garth 


#10
Aug2805, 11:41 AM

P: 786




#11
Aug2905, 12:09 AM

Sci Advisor
PF Gold
P: 9,384

Since 1998 [re: Perlmutter, et al], supernovae redshift data indicates the expansion of the universe slowed down for the first several billion years after the BB [as expected], and then decided to speed up [totally unexpected]. This led to the dark energy hypothesis [which is analogous to Einstein's cosmological constant].



Register to reply 
Related Discussions  
About space expansion  Cosmology  93  
Speed of Space Expansion  Astronomy & Astrophysics  16  
Is expansion of space relative?  Special & General Relativity  2  
The expansion of space  General Physics  1  
How you picture the expansion of space.  Astronomy & Astrophysics  19 