I admit, this is going to sound like a horribly stupid question to the real physicists here, but i must confirm these basics before i may continue to understand further concepts regarding the universe and what i am reading about.


1) The universe is expanding at speeds greater than that of light, or at the speed of light?

2) How is "expanding" defined? I'm guessing the matter within the universe is not exceeding light, so is it just empty space that expands?
(please, if i am misunderstanding the concept of expansion please do let me know)

3) If it is expanding greater than or = speed of light, is there some sort of time dilation due to expansion (at or near the edges of expansion)?
I have only ever touched upon time dilation last year in physics 11, barely even touched upon the basics, so i do not know if the same concept or rules apply for this situation? Or how they may or may not be applied?


Sorry again for this silly question, but i have yet to be educated on the subject and would greatly appreciate any help. My physics teacher is practically next to useless for this kind of stuff because he has forgotten most of the stuff he has learned but does not teach in high school... Understandable to forget what you do not use on a daily basis, however unfortunate for me .

Michael

Wondered the same thing myself.

I also took a shot at the Big Bang Theory many years ago. Not to dispute it, albeit still suspicious, just to add the effect of gravitational lensing as a factor in the redshift expansion concept.

Dark Matter, the existence of which is largely accepted, but the element which makes it viable is still unknown. I suspect metallic hydrogen, but just guessing. Anyway, the increasing amount of redshift in light from increasingly distant stars is always given as evidence of an expanding universe, which is thought to have expanded from somewhere and thus the foundation for the Big Bang Theory.

I once attended meteorology classes for personal interest at the University of Colorado in the 1970s. There, George Gamow is revered and he was a proponent of hydrogen being a major factor in space. He died in Boulder, CO in 1968 after an illustrious career at U of Colo.

At one point in a class discussion on the possibility of there being some sort of weather in space, I proposed that hydrogen clouds between Earth and other Suns might function as gravitational lenses and deflect light from distant stars so it actually traveled further than it would have in open space with no hydrogen clouds present to act as gravitational lenses. I asked if this bending of light, which obviously increased the distance light would have to travel thru space, might also produce a redshift in the light from distant stars. If so, I suggested the redshift was more of a measure of distance than expansion and there might be NO expansion of space, only cumulative light bending, which produced the increased distance light had to travel as it progressed thru increased distance.

Needless to say, I was told the idea was silly and the redshift of light is factual evidence of an expanding universe. Or is it?

I'll sure be interested in the answers, Regards, Stewart1

Michael J

The expansion is not actual velocity in regards to time dilation. The space between gravity bound systems is growing larger, the gravity bound systems(galaxies, groups and clusters) have an intrinsic velocity(their velocity through their own local space) and an extrinsic or apparent velocity(the velocity that they APPEAR to be moving away from us) that is mostly due to the expansion of the space between us and them. While it may appear that they are moving away from us at near light speed(and, in fact they are), they are not actually moving at relativistic velocity in relation to their own space so no dilation effects occur(or, at least very small effects due solely to their movement relative to their own frame, not ours).

We seem to live in a privileged time, in that the farthest galaxies are not yet traveling above lightspeed in relation to us. This may not BE true, but some interpret our observations that way. The Universe seems to be about 48 billion light years across. This includes the 13.7 billion lys that light has traveled since the BB+the amount which the Universe has expanded in those 13.7 billion years(including the initial inflation period)X2, if I am not mistaken. Of course, the geometry of the Universe appears to us to be inside out(IE, no matter which direction we look we are looking at the "center"(the BB) where it all started).

Another thing to consider is that when we look into deep time we are seeing those galaxies as they were 13.7 billion years ago, not as they are today. The light that is leaving them today may well never reach us as in another 24 billion years they will have apparent velocities greater than light speed. Also, when they observe our galaxy, they see it when it was a violent, young quasar, not as the relatively calm spiral galaxy we know and love today.

Even in our own neighborhood this is true. Eta Carina is a huge star in the last stage of it's short life. We keep watching it, expecting it to blow up at any time. But, in all likelyhood, it has already done so, but being so far away, the light of that event has not yet reached us.

Hope I haven't just confused you further.

Grumpy

No confusion Grumpy, i think i am understanding what you're talking about.
I understand what you are saying that they are "moving from us", but not actually in relation to the space they are in. This makes sense to me anyways!

For the speed at which we observe these galaxies to be moving from us, this is actually deceiving for they are not presently as they appear? I think i understand this, i'll just keep re-reading this until it clicks. My mind is a bit occupied with final exams coming up in a few days !

I think your example of the star has made what you are saying much easier to comprehend for me. Although "everywhere" being the center will take some more studying for me to fully wrap my head around. I'm am still influenced by our earthly physics, these concepts are quite wild for me to digest!
Extremely interesting, thank you Grumpy for taking the time to explain it to me in "simple terms" !

Michael