Is the Expanding Universe Slowing Down According to Age?

AI Thread Summary
The discussion revolves around the concept of the expanding universe and its relationship to the age of observed galaxies. It highlights that while farther galaxies appear to move away faster due to the expansion of space, they are also seen as they were in the past, not as they currently are. The Hubble constant indicates that objects at the same distance recede at the same rate, supporting a uniform expansion. The universe's expansion is currently accelerating, meaning ancient galaxies were observed when the expansion rate was slower, but this does not imply that the universe is slowing down overall. The conclusion drawn is that the perceived relationship between a galaxy's age and speed does not indicate a deceleration of the universe's expansion.
meatym
Messages
5
Reaction score
0
i've seen many documentaries. most recently nova had one on the expanding universe which prompted me to send them (nova@wgbh.org) the following:

based on the nova shows I've seen, they suggest the universe is expanding.
farther objects are observed as moving away faster than closer objects.
but the farther objects are also older, so according to age, wouldn't that mean that the universe is slowing down?
also, are all objects at a similar distance moving away at a similar speed?
===
they sent a response that said they forwarded to their producers, but in the meanwhile, i thought i'd look elsewhere...

thanks in advance for any responses.
 
Astronomy news on Phys.org
Farther objects are older to US because we can only observe them as they were in the past depending on how long light from that object took to get to us. But if you take a constant slice of time at any instant and analyze the observable universe (this is all mathematically) all objects, and I mean at the large where isotropy and homogeneity are preserved, are of course the same distance in time from t = 0. The rate at which objects recede from whatever you pick to be the origin (since you do have that freedom) is directly proportional to the distance between the object and your chosen origin. Objects all at the same distance from "the origin" will recede at the same rate.
 
The answer to your last question is yes. The Hubble constant which is used to measure the expansion of the universe is based on an expansion speed per distance from us.

So, picture the universe expanding uniformly in all directions. So, the further away a particular object (e.g., galaxy) is, the more expanding space there is between you and it. So it appears to be moving away faster than something which is closer.

And due to the finite speed of light, the older it appears to us (not actually older...it's just that we're seeing it's past because light from its present state has not reached us yet).

So, the ancient galaxies we're seeing at great distances are not causing the universe to slow down. But since the universe expansion is actually accelerating, I suppose we're seeing those ancient galaxies from a time when the universe was expanding at a slower rate.

Clear as mud?
 
Phobos said:
But since the universe expansion is actually accelerating, I suppose we're seeing those ancient galaxies from a time when the universe was expanding at a slower rate.
Clear as mud?

but since we are seeing the galaxies as they were a long time ago - the further away, the further back into the past - and the older the image, the faster it is moving...
that would imply to me that the galaxy's age is inversely proportionate to it's speed.
the newer the image, the slower it is moving. wouldn't that mean that things are slowing down as time goes on?
 
Last edited:
thanks for answering the other quetion, btw
 
Is a homemade radio telescope realistic? There seems to be a confluence of multiple technologies that makes the situation better than when I was a wee lad: software-defined radio (SDR), the easy availability of satellite dishes, surveillance drives, and fast CPUs. Let's take a step back - it is trivial to see the sun in radio. An old analog TV, a set of "rabbit ears" antenna, and you're good to go. Point the antenna at the sun (i.e. the ears are perpendicular to it) and there is...
This thread is dedicated to the beauty and awesomeness of our Universe. If you feel like it, please share video clips and photos (or nice animations) of space and objects in space in this thread. Your posts, clips and photos may by all means include scientific information; that does not make it less beautiful to me (n.b. the posts must of course comply with the PF guidelines, i.e. regarding science, only mainstream science is allowed, fringe/pseudoscience is not allowed). n.b. I start this...
Back
Top