Birth of the Universe

[DMike]

It is frequently stated in discussions that when viewing very distant galaxies we are viewing events close to the birth of the universe (big bang 13.7 billion years ago). Surely this is impossible as it would imply that our location existed prior to the birth of the universe or somehow our location traveled faster than the speed of light to its current location enabling us to view events taking place at that time.

 

[bushwhacker]

Sorry DMike. it implies nothing of the sort. What we are looking at is the light that left the distant object at that time.We formed ~4.5 billion years ago and that light is just now reaching us.

 

[DMike]

Hi,

I am obviously being a bit naive here (a bit of a newbie to this). Can I ask this question - what it the oldest object that we can theoretically view? (given our current location, speed of light, big bang, etc)

DMike

 

[MeteorWayne]

In theory, we can observe objects from about 13.3 billion years ago, after the Universe became transparent. The current record is a bit short of that so far, but when James Webb Space Telescope (hopefully) launches in a few years, we should get there.

 

[DMike]

Hmm - still not clear. Assuming the big bang took place 13.7 billion years ago and we can maybe view light that left an object 13.4 billion years ago that would mean that (assuming our location, OK dust at the time, was created at the same time) in the 0.3 billion years differential we are now in a location where we can view events 13.4 billion years in the past. The maths doesn't seem to add up. Surely any light created 13.4 billion years ago would have long passed us as we were at that exact point in time very close (relatively) to the object emitting the light.

 

[MeteorWayne]

That's not how it works. We are now 13.3 billion light years from everywhere else in the Universe that existed at that time. Those parts that have moved in the same direction as we did are closer.

 

[DMike]

I am aware of theories like " isometric embedding" - light taking an asymmetric route to reach its destination and not an A -> B direct route. However even this theory would have difficulty in accounting for a 13.4 billion light year distance (observable now from one point in space to another) between objects given a start time of 13.7 billion years ago for everything. As indicated in the previous post if we went back to when the light left the distant object 13.4 billion light years ago our observation point at that time would have been considerably closer to the object than it is now and basic maths would indicate that light leaving the object then would have long overtaken us.

To re-iterate a previous question: what is the age of the oldest object we can theoretically observe? (given speed of light, expansion rate of the universe, date of big bang).

 

[MeteorWayne]

I already answered that once.

I'd strongly suggest you make some more effort to understand the current theories about the subjects you are speculating on.

 

[adrenalynn]

Start at a point. Expand in all directions away, and simultaneously, start the clock, then shine a light backward from that expansion toward a center. It's a fairly simple thought exercise to see that the light reaching us at any given moment is close to zero delta from the start of the clock and simultaneously, all points exist as zero points.

Because we didn't have simultaneity as far as light is concerned, we can also observe that we can't ever reach a true zero delta. So we can also make a pretty good hypothesis for when the whole thing ceased to be opaque

The "date of the big bang" made me giggle a little. What's the date that time began? Ummmm - Zero. Before time we didn't have time so by definition time is zero.

 

[SpeedFreek]

To re-iterate a previous question: what is the age of the oldest object we can theoretically observe? (given speed of light, expansion rate of the universe, date of big bang).

The universe first became transparent, with a flash of light everywhere, around 13.66 billion years ago (MW's figure was a little low, if that is what he was referring to). The event was called recombination and is thought to have occurred around 400,000 years after the Big-Bang, which occurred 13.7 billion years ago.

We see that flash of light today as the Cosmic Microwave Background Radiation (CMBR), coming in from all directions. This is the oldest light we have detected, and it is predicted to be the oldest possible light we would be able to detect, as photons were only able to move freely through the universe after recombination. As this light was emitted everywhere in the universe, it has always been hitting us, and always will (or at least until the expansion of the universe stretches it until it is pretty much invisible - so far it has been stretched from visible light into microwaves!). As time goes on, we are being hit by CMBR that was emitted at increasing distances.

The oldest actual objects (rather than the light from a universal event) we have seen are dim and distant galaxies, seen as they were around 13 billion years ago.

Have a read of the pdf file linked in my signature, it explains how the expansion of the universe can mean that light originally emitted quite close to here can take billions of years to reach us, due to the expansion of the distance between the original source and ourselves. Basically, early in the history of the universe, objects were receding due to the expansion of the universe faster than their light could make progress towards us (from our point of view!) and it took a while (and a decelerating universe) for the light to catch us up!

 

[adrenalynn]

>> (from our point of view!)

And from every other point of view except their own.

 

[DMike]

Speedfreak,

Interesting and thought provoking article (I hope some of the other respondents have found the time to read it!). Addresses, or offers a theoretical account for, some of the issues behind the points raised in my initial posting.