Hubble Deep Field theory.

A while ago, folks who had time on Hubble pointed the telescope to a patch of black space for a couple of weeks or so, and it turned out that the picture was full of Galaxies, presumably only a few hundred thousand years old and possibly it reflected the early universe, with new galaxies seemingly everywhere. Is this part true?

This got me thinking… I don’t know much about photography, so my questions might seem very elementary. Forgive me.

But, as they looked at the developing picture each night, did astronomers begin to see the first glimpses of galaxies forming on the picture, while others remained invisible until later in the process? If it correct to assume that each one appeared when their light finally reached the HST? If the camera was permitted an entire year of being exposed to the same patch of darkness, how far back could we theoretically see?

And is that what actually happened? Light that finally appeared in the deep field had been traveling so long, that unless film had been exposed on that spot long enough to capture it, we would have missed it, and as a result never see the galaxies that were found?

Is the light created by the BB gone, never to be seen? Or if we were able to pick the right part of the sky to stare at, would it be possible to see seconds after the big bang? Or are those images gone forever?

Partly. The Hubble Deep Field shows galaxies 1 billion years after the big bang, and the Hubble Ultra Deep Field at least 400 million years after the big bang.

No, you’ve got that wrong. The long exposure time is necessary because the light is very faint. Regular cameras in regular conditions do the same thing, and will use a longer exposure time in lower light. (Assuming the same aperture.)

The universe was so dense, and the state of matter such that the universe was opaque for 380 000 years, so the light from that era is gone, never to be seen. There’s a theoretical possibility we could at some time in the future observe neutrinos from that period, but it’s way beyond current technology to do so in a way the gives us any information.

It seems very unlikely that the discovery process would be triggered by the actual light from an actual galaxy arriving just in time for the sensor to catch it. I think it’s more a question of looking at the same spot long enough (or repeatedly enough) that the signal-to-noise ratio improves and you can finally distinguish between what’s noise and what’s a galaxy.

Also, if the first light had only just arrived, it would imply that the galaxies sprang into existence fully-formed. At no point would there have been nothing, immediately followed by a whole galaxy.

To elaborate on what **naita **said, when the universe first sprang into existence it was filled everywhere with hot plasma. It was so “foggy” that light couldn’t travel any significant distance. As we look at more distant objects we’re looking back in time. The most distant (and therefore oldest) thing we can see is the hot “fog” that filled the universe for the first several hundred thousand years. The light from that “fog” is called the cosmic microwave background radiation.

OK. I think I understand this. It makes sense to me anyway.

So here’s my question… we have something that can pick up the light from the early universe, right after the big bang (relatively speaking). So, if we have the time and can pinpoint the right spot in the universe, can we theoretically see the “fog” clear?

What I am having trouble understanding is this… if images move at the speed of light (since they are made up of light) across the universe, the image must have a finite viewing life, correct?

so if this is the case, how do they date the “fog” photo to several thousand years? are they saying that the first several thousand years of light the universe has given off are no longer visible? I guess I’m having trouble understanding how long a light image will be able to be captured before it’s gone forever.

Assuming for a moment there was no “fog” when the universe was young, just exactly how far could we see back, exactly? i understand that it wouldn’t be possible to see the exact moment of creation. But how soon after would we be able to see if the “fog” didn’t exist?

Im sorry if this didn’t make sense. I’m having trouble trying to formulate the question because I am having a tough time putting words down to what I’m trying to convey. I hope someone out there can interpret what I’m asking.

If we look at the Sun, we see it as it was “8 minutes ago”, but we still see it constantly age and will see it until it inflates and burns us to cinders. If we look at Alpha Centauri, we see it as it was “4 years ago”, but we still see it constantly age and will see it until we burn to cinders or it blows up, whichever comes first (I don’t know, it might not even blow up). If we look at the Andromeda galaxy we see it as it was “2.5 million years ago”, but we still se it constantly age. When we look into the deep field, we look further back in time, for one definition of back in time, but we’re still seeing the objects age and change “in real time”.

When we get that far out we run into the complications of the expansion of space and the finite distance to the edge of the observable universe. But I don’t think that’s where your question lies.

The fog is everywhere we look in the sky, behind all the stars and galaxies. And we’re always seeing the time when the fog clears, because the light from closer patches of fog has already passed us, and the light from further patches of fog is hidden by the fog that’s just clearing.

The duration of the fog has been calculated through complex simulations of the dynamics of the early universe. Basically scientists say “We see these percentages of elements, and the fog has these sorts of swirls in it … how long would it have taken for that state affairs to come about?”

For a few hundred thousand years after the big bang, the universe was so hot and dense light couldn’t travel any significant distance. Then it spread out and cooled off. The last light from the fog that existed where we are now is long gone. But it’s taken a long time for the light from very distant patches of fog to reach us. That’s what we’re seeing right now.

It depends on what you mean by “see”. There were high-energy photons bouncing around in the primordial plasma less than a second after the universe came into existence. If they could magically pass through the plasma we’d see a different version of the cosmic microwave background – a different dim glow filling the entire sky and lying behind all the stars and galaxies.

Alan Parsons Project Temporalia

When you look into a night sky
You see the stars far away
You’re seeing them because of the light
Which travels from them to you
Now it takes time for light to travel here

So what you’re doing is seeing the stars as they were in the past
The amount of time it has taken for the light to reach us
And the further and further away those stars are
The further back in time you are looking

Now you are seeing a star that is say six thousand years ago
Imagine somebody on that star looking at us
They would be seeing us as we were six thousand years ago
Which of those two is now?

So space and time are linked together
As we are looking across space, we are looking back in time

Let’s do an analogy with sound.

We know sound travels at about 3 second per km (5 seconds per mile). If we could build sensitive-enough equipment, we could listen to sound from 10 km away, and learn what was going on 30 seconds ago. With better equipment, 100 km would allow us to look 300 seconds or 5 minutes into the past. But there’s a limit to all this: even with perfect equipment we can’t listen beyond the farthest point on the planet, in this case on the other side of the Earth, and the corresponding time is about 17 hours in the past. It doesn’t mean that the Earth was created 17 hours ago, just that the audio information from beyond 17 hours is no longer available.

In a similar way, when we see very distant objects, we can determine how old the images are based on their distance (red shift, etc.). It so happens that these objects are so far away that their age is commensurate with the age of the universe. That doesn’t mean that there’s always something that’s farther away, or that the photons containing light from the Big Bang are still available.

Another question popped into my head about the light from the earliest parts of the big bang are long gone…

Does this prove that the universe does not double back on itself? I.e. If I was in a spaceship and headed in one direction at warp speed, eventually my ship would come back to the place it started. So the universe must not be a sphere, or we have not been able to reach the horizon yet.

What I find really interesting is that if the universe IS round and one can head in one direction forever and get back to the starting point, wouldn’t the image carrying photons continue on forever also?

To be honest I struggle with this stuff but I also enjoy thinking about it too. Strictly, the Universe is saddle shaped - at least Einstein thought so. Nevertheless you are correct in saying that a journey to the end of the Universe would bring you back to your starting point. Sorry though, I can’t think of the answer to your photon point. :smack:

Just to elaborate slightly, when the very early Universe cooled and expanded sufficiently, photon decoupling occurred. It was at that point light escaped.

We may one day be able to see earlier periods by looking at gravity waves.

And just because it boggles my mind - we only see the visible Universe for a distance of 13.4 billion lightyears. The actual Universe is larger - 16 billion lightyears - but the galaxies at that range are expanding away faster than light. We will never see them.

If the Earth was expanding all over at a uniform rate, it could mean that some parts of the map would be moving away from you at a speed greater than that of sound - and so you’d never be able to observe or communicate with those parts.

And I think that’s the same problem with light and the universe - some parts are moving away from us too fast - so any information (light, gravity, whatever) can’t get here.

Only for a quaint definition of “the actual Universe”.

It’s important to note that this only applies to “movement” due to the expansion of the space in between the observer and object. You can still hear a plane moving at mach >1 in a nonexpanding or non-moving atmosphere.