Can anyone explain ?

[BertiWooster]

// Cosmologists are able to measure light and background background radiation from the big bang that has taken 13.6 billion years to reach earth.//

Can someone please explain - when it is stated that light from the big bang has taken x years to reach the earth .

Afterall the big bang was not at a point x distsnce from where the earth is located .

I hope you can see what i am trying to understand

[ll_billym]

After not being able to find a link explicitly answering your question I am giving you my understanding of it - and I may not be entirely right!

The first thing is that the radiation that is measured was actually created about 400,000 years after the big bang, before that the universe was too dense for light and radiation to exist for any length of time. We cannot 'see' any universe activity from before this time although there are thoughts that measuring gravity waves from this time will allow us to do this in the (distant) future.

The radiation that is measured didn't actually travel from a single point TO the Earth, we are not special in that respect! Rather it comes to us (and everything else in the universe) from all directions.

Think of it as we are detecting 'light speed' signals that are hitting us now that were generated from an event that happened 13.7 billion years ago. The actual signals that we are measuring have indeed travelled 13.7 billion light years in distance to get to us but that is just because we are measuring NOW, if we were measuring 10 billion years ago, the signals would have only travelled 3.7 billion light years to get to us but this has nothing to do with the actual 'size' of the universe either back then or now.

Be interested to see what people think of my understanding of it all! Interesting question...

[BertiWooster]

What about this explanation

When the big bang occurred the universe expanded in all directions at a rate , far exceeding the speed of light i.e the light from the big bang

The earth was formed some time later in the expanding universe - so the light from the big bang / and subsequent periods in time is catching up with us / reaching the earth .

I'm not even sure i quite understand my explanation

[mibn2cweus]

The light that is the MBR is not attributed to a singularity but from a time thereafter when the universe first became transparent.

While the present day expansion we observe points to a singularity, all we can confirm at this point in time is that the universe was once in a very hot and highly compressed state allowing for the condensation of basic forms of matter out of energy as it expanded and cooled. As you say, this expansion did not take place at some point in the universe but throughout the universe, therefore, what we currently observe from our place in the universe as microwave background radiation is light from the distributed glow from that distant past as it arrives at our position in an expanding space from various distant points all around us.

If all of this light originated from a single distinct point and time in space it would all hit us at once or not at all.

[ll_billym]

Bertie:- Your explanation above is wrong. Don't think about it as detecting signals 'from' somewhere. Rather it is detecting signals from 'everywhere'.

The signals were generated everywhere in the universe at a particular point in TIME rather than a particular point in space.

Imagine a the earth is inside a large sphere that is 13.7 light years in radius, we are detecting signals that were generated at all points in space, at the same time, from every point on that sphere.

Now imagine another planet that again has the same sphere around it, but they are at a completely different point in space to Earth, they detect the same types of signal from all points on THEIR sphere.

It is to do with time and not distance.