How Would We Know?

[emperor_of_localgroup]

It is about that expansion of the universe again. I raised a minor question before about the nature of this expansion. So far all cosmologists, I guess, think the expanded portion of the univ has the same property as the old portion. In other words, space-time does not change even though the universe is expanding.<br /><br />My question is how would we know whether the spatial dimensions and temporal dimension are also changing with the expansion fo the universe? If spatial dimension increases, so will our measuring instruments. If temporal dimension increases (slower time), so will our clocks? Whatever measuring systems we use, 1 sec before expansion is the same as 1 sec after the expansion. All changes are taking place in proportions. Am I missing something here? Can someone wake me up? <div class="Discussion_UserSignature"> <font size="2" color="#ff0000"><strong>Earth is Boring</strong></font> </div>

 

[a_lost_packet_]

<font color="yellow">emperor_of_localgroup -My question is how would we know whether the spatial dimensions and temporal dimension are also changing with the expansion fo the universe?</font><br /><br />If spatial dimensions changed I would think we would recognize it. None of our ideas based on one dimension of time and 3 dimenions of space would be applicable. Either we'd see very weird things happening in some local area or, in the case of universal change, we might even cease to exist. For instance, we may be able to detect an area in space that has "changed" in some way if we had viewed that area previously. By noting the changes and applying what we know, we could determine whether or not our 4 dimensional thinking applies. Radiation measured from star xxx when compared to previous measurements now shows unexpected results. Subsequent measurements reveal that nearby bodies are under a similar influence while far-flung objects do not seem to be effected. etc.. If spatial dimensions changed Universally, I don't think we'd be around to notice.<br /><br /><font color="yellow">So far all cosmologists, I guess, think the expanded portion of the univ has the same property as the old portion. In other words, space-time does not change even though the universe is expanding. </font><br /><br />I believe that most would say this is indeed the case. ie: The "rules" for our Universe are not changing due to expansion.<br /><br /><font color="yellow">If spatial dimension increases, so will our measuring instruments.</font><br /><br />Not necessarily. Of the classical, four, fundamental forces, Gravity is the weakest "force." (It's not really a force per se.) The fundamental forces that are maintaining the complex arrangements of atoms, radiation et al, are not being locally effected by the expansion of the Universe. The idea is that the expansion is being fueled by something acting causing "negative pressure" which appears to act the same as <div class="Discussion_UserSignature"> <font size="1">I put on my robe and wizard hat...</font> </div>

 

[kmarinas86]

<font color="yellow">Whatever measuring systems we use, 1 sec before expansion is the same as 1 sec after the expansion.</font><br />...<br /><font color="yellow">My question is how would we know whether the spatial dimensions and temporal dimension are also changing with the expansion fo the universe?</font><br /><br />The presence of gravity is a like a friction which slows down time. Therefore the "distortions" of space and time (i.e. rates of "gravitational acceleration" and "change") are a function of the various densities of distributed matter in the universe.<br /><br />Gravitational Time Dilation<br />http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/gratim.html#c4<br /><br />Expansion must be caused by repelling forces. These forces can be cancelled out by the presence of gravity at smaller scales. The density of energy over galactic scales is smaller than the density over smaller, stellar scales (because of the greater distances between objects). Therefore, the effect of gravity on expansion is weaker at the galactic scale, which means that expansion is greater at that level.

 

[kmarinas86]

<font color="yellow">So, to get back to the spirit of your questions, if other galaxies are accelerating in relationship to our referrence point, then aren't those galaxies clock's always running slower than ours.. from our point of view?</font><br /><br />If the galaxy is accelerating away from us, its clock is not just slower, but slowing down too.<br /><br /><font color="yellow">Couldn't an increase in "temporal dimension" equate to acceleration?</font><br /><br />Temporal Dimension: The increase in temporal dimension, or the lengthening of the second, is like how the second is "lengthed" in a black hole relative to our vantage point.<br />The answer to your question: An increase in velocity, which is equivalent to acceleration, increases the temporal dimension.<br /><br />Time Dilation: http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html#c2

 

[a_lost_packet_]

<font color="orange">a_lost_packet_- So, to get back to the spirit of your questions, if other galaxies are accelerating in relationship to our referrence point, then aren't those galaxies clock's always running slower than ours.. from our point of view? ... Couldn't an increase in "temporal dimension" equate to acceleration? </font><br /><br />kmar - They were really just illustrative, rhetorical questions placed for emphasis. But, thanks for the reply! <img src="/images/icons/smile.gif" /><br /><br /><font color="yellow">kmar - If the galaxy is accelerating away from us, its clock is not just slower, but slowing down too. </font><br /><br />Slowing down.. relative to what? <img src="/images/icons/wink.gif" /><br /><br /> <div class="Discussion_UserSignature"> <font size="1">I put on my robe and wizard hat...</font> </div>

 

[kmarinas86]

<font color="yellow">Slowing down.. relative to what?</font><br /><br />Anything, because it's clock is slowing down. Even thought its slowing down, that does not mean its clock is the slowest of all. It could still be faster than another clock and yet still slowing down, as long as the object is accelerating.