[matt821 (OP)]

Hi all,

Can someone explain to me how we are where we are in the universe if light from the time of the big bang or close to that time hasn't reached us yet?  Is that a stupid question?  Didn't everything get thrown out at the speed of light from the beginning or are other factors at play?  Started thinking about it because the James Webb telescope is supposedly going to look for light from the earliest stars which hasn't reached us yet.

Thanks for the insight.

[Halc]

Can someone explain to me how we are where we are in the universe if light from the time of the big bang or close to that time hasn't reached us yet?

You seem to be thinking of it as an explosion from one point in space, rather than the big bang happening literally everywhere and just the space increasing between things.
The universe has never had a finite size, and the earliest light was emitted everywhere, not just from one point, so that light is still going from everywhere to everywhere else, and redshifting as space expands.
The earliest light that we see (from further than any star we can see) was emitted when the universe was about 380,000 years old, before which it wasn't transparent.

Didn't everything get thrown out at the speed of light from the beginning

No. Most stuff (like matter) was reasonably stationary all along, and just the space between stuff expanded without anything particularly moving anywhere. Sure, light and other things without proper mass moves (locally) at c, but not the gas, stars, etc, most of which move (called peculiar velocity) at under 3% of c relative to the cosmological frame in which all large scale distances are expressed.

Started thinking about it because the James Webb telescope is supposedly going to look for light from the earliest stars which hasn't reached us yet.

If the light hasn't reached us yet, no telescope is going to change that. Bigger telescopes don't detect light that isn't already right here, they're just more sensitive to low intensity light and have better resolution.

[chiralSPO]

The JWST is looking for evidence of (or against) the big bang. Rather than saying anything definitive about the big bang (since that is the theory to be tested), I will instead frame it around what we do observe, and how that can be interpretted.

As far as we can tell, there is no edge to the universe, and it's essentially the same everywhere (on a large enough scale). This means that for any distance you choose (greater than the distance to the sun), there are some stars closer than that distance, and some (infinitely many?) stars farther than that distance.

Because light travels at a fixed speed in vacuum (again, as far as we can tell, but this has been very well confirmed), that means that by selecting a distance (light years), you have also selected a time (years) for how long it will take the light from that star to reach you.

If the universe were infinitely big, infinitely old, and always had stars dispersed throughout at the same density, then the sky would be completely filled with light (because light would be reaching us from every direction), and we'd be baked to a crisp. This clearly ins't the case, so at least one of those stipulations must be wrong.

We cannot find any evidence that the universe isn't infinitely big (and we've been trying!)

But there is evidence that the universe was not always as it is now. As we look farther and farther away it appears that there is a boundary beyond which we cannot see. One explanation is that nothing in the universe is older than some limit of X years (something like 14 billion years, I think?), and that if we look more than X light years away, there won't be any starlight to see, because light from those stars can't have reached us yet.

There is another complication. It also appears that light from distant parts of the universe is redshifted. And the redshift appears to be more significant the farther away something is. One explanation for this is that everything is moving away from everything else (expanding distances between everything). Extrapolated back, and taken together with the previous paragraph, we expect to find that X years ago the universe was much more densely filled with stuff, and it has been moving apart since. This is the essence of the Big Bang Theory, as I understand it.

The problem is (and this is one of the things that the JWST will help with), is that there are inconsistencies in our observations and theories about how fast the universe is expanding, and whether the process is speeding up, slowing down, or constant (or something else?). There are also seem to be many problems with boundary conditions and getting agreement between models of "first" few attoseconds with the "first" few microseconds and the "first" few years. (this might be the "Didn't everything get thrown out at the speed of light from the beginning" bit you were talking about)


There are other theories that try to explain these observations, but none is complete, and many have significant shortcomings or seriously challenge our understanding of everything (the hallmark of either a terrible theory or an ingenious and paradigm-shifting revolution... and it's almost always the former)

My personal (non-expert) suspicion is that our understanding of time is flawed, and that many of the apparent problems with the Big Bang, and the interpretation of the Hubble Constant(s) arise because of this flawed understanding.

I previously proposed one alternate model here:  https://www.thenakedscientists.com/forum/index.php?topic=73163.0
(if you like math, you might find the equations interesting; either way the discussion should be entertaining)

But alternatives to the Big Bang Theory are not only limited to non-experts like myself. Here are a few ideas from better respected experts:

https://www.livescience.com/universe-had-no-beginning-time
https://www.space.com/38982-no-big-bang-bouncing-cosmology-theory.html
https://www.quantamagazine.org/cosmologists-close-in-on-logical-laws-for-the-big-bang-20211110/

[matt821 (OP)]

Hi all, thanks for the detailed replies. Yes I think I was assuming the universe started at a point so perhaps this is what I was thinking. Perhaps confusing as the article said the telescope was going to focus on one patch of sky as if it was aimed at the starting point in space if you like. I do remember the old expanding balloon analogy where everything expands away from everything else. Interested to see the pictures it produces anyway! Thanks again

[evan_au]

if light from the time of the big bang or close to that time hasn't reached us yet?

The Cosmic Microwave Background Radiation (CMBR) was emitted close to the Big Bang (estimated at around BB+400,000 years).
And that radiation has been reaching us for the entire life of the Solar System.
It was emitted when the temperature of the universe dropped below about 3,000C.
It has now been extremely red-shifted, so it now reaches us in microwave frequencies.
See: https://en.wikipedia.org/wiki/Cosmic_microwave_background

the James Webb telescope is supposedly going to look for light from the earliest stars

The specialty of the James Webb Telescope is that it can see infra-red light much better than the Hubble telescope, or ground based telescopes (which have to deal with the atmosphere).
That means it can see red-shifted light from early stars.
Note that these stars are so distant that it will not be able to detect individual stars, but it will be able to detect early galaxies.
Also important, it should be able to detect more distant supernovae, so we can improve our estimates of the impact of Dark Energy.
It will also be much more sensitive to red dwarfs and brown dwarf stars, and be able to see though dust clouds to the center of our galaxy, and into star-forming regions of our own galaxy.
https://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Features

Let's hope they manage to launch this time - and sucessfully commission it!

the telescope was going to focus on one patch of sky

I am sure that astronomers will be queueing up to use this new window on the universe, with objects of interest all over the sky.
It's just that if they are to get good images of these very faint early galaxies, it will need to spend a lot of time staring at one patch of the sky.
Our current best image of the early universe comes from the Hubble Deep Field experiment, which spent around 150 hours staring at one patch of sky. But 150 hours is a long way from "all the time"!
https://en.wikipedia.org/wiki/Hubble_Deep_Field

which hasn't reached us yet.

In 2023, the Vera Rubin telescope is expected to begin operations.
All light that it sees will be light that hasn't reached us yet.
If the light had reached us already, then it would have arrived before the telescope began operations.
That's why astronomers are always looking backwards in time - even when they are observing objects in our own Solar System.
https://en.wikipedia.org/wiki/Vera_C._Rubin_Observatory

[chiralSPO]

Oh, and here's another good pop-sci article about an alternative theory of the early history of the universe: https://bigthink.com/starts-with-a-bang/big-bang-beginning-universe/