Ok at the moment we call the Big Bang the universe was infinitely small, everything concentrated at a single point. Then it started expanding and this process still goes on. We know that the expansion of the universe is accelerating and so the expansion of the universe must be going on faster now than it did when the big bang started. The universe is making a transition from infinitely small to infinitely large, am I correct? If this is correct, does it not make sense to define the big bang as an ongoing process in which the universe goes from infinitely small to infinitely large, rather than a single event which occurred about 14 billion years ago?

From my layman's understanding, the BB was 'the event', what we are in is the expansion.

We are all getting bigger every second, including women's bum's.

John

z8000783 wrote:We are all getting bigger every second, including women's bum's.

John

Fortunately, locally bound subsystems aren't expanding along with the universe, so the example you quote isn't applicable. I can hear your refutation now though....."just walk round Swindon town centre on Saturday night...."

BlackBart wrote:From my layman's understanding, the 'Big Bang' was the start of the expansion of the universe from a singularity. As we can see that galaxies are moving away from each other to this day, the expansion is still occurring. Therefore the 'Big bang' is still going on.

We don't know if the universe started from a singularity. At Planck's time, our theories ( Relativity and quantum mechanics) break down. So what happened before 10-44 seconds is anyone's guess.

twistor59 wrote:

z8000783 wrote:We are all getting bigger every second, including women's bum's.

John

Fortunately, locally bound subsystems aren't expanding along with the universe, so the example you quote isn't applicable. I can hear your refutation now though....."just walk round Swindon town centre on Saturday night...."

Pfft.

I'm in Michigan...beginning of December...snow on the ground...The extra winter insulation is making itself seen.

But, if you keep that to yourself, the "Big Bang" could still happen.

zaybu wrote:

BlackBart wrote:From my layman's understanding, the 'Big Bang' was the start of the expansion of the universe from a singularity. As we can see that galaxies are moving away from each other to this day, the expansion is still occurring. Therefore the 'Big bang' is still going on.

We don't know if the universe started from a singularity. At Planck's time, our theories ( Relativity and quantum mechanics) break down. So what happened before 10-44 seconds is anyone's guess.

Exactly, although it isn't precisely that they break down, it's that they contradict each other, in that one of them (relativity) predicts a singularity while the other (QM) tells us that the singularity is an asymptote. Until such time as they can be unified and render a sensible result, we can't begin to predict what happens.

BlackBart wrote:From my layman's understanding, the 'Big Bang' was the start of the expansion of the universe from a singularity. As we can see that galaxies are moving away from each other to this day, the expansion is still occurring. Therefore the 'Big bang' is still going on.

I follow the same line of thought but come to a different answer.

The Big Bang is the name for the trigger that started expansion, so expansion is the result of that event rather than being the Big Bang itself, so the Big Bang is finished.

I would normally say that the bang is still going on, but this is less than uncontroversial, not least because we're in a period of accelerated inflation, so while it can be said to be still happening, there is slightly more to it than that because of the added impetus.

hackenslash wrote:I would normally say that the bang is still going on, but this is less than uncontroversial, not least because we're in a period of accelerated inflation, so while it can be said to be still happening, there is slightly more to it than that because of the added impetus.

Nah it finished long ago. Isn't 30s the average time for a bang ?.... oh....wait....

hackenslash wrote:I would normally say that the bang is still going on, but this is less than uncontroversial, not least because we're in a period of accelerated inflation, so while it can be said to be still happening, there is slightly more to it than that because of the added impetus.

Then isn't that saying that 'big bang' = 'inflation'?

I'm more than prepared to be shown wrong here, but my take on it is that the rather poorly named 'big bang' is the trigger rather than the inflation.

twistor59 wrote:Fortunately, locally bound subsystems aren't expanding along with the universe, so the example you quote isn't applicable.

Come on twistor, we all know that the earth is expanding!

One could say that the term 'Big Bang' refers to the start of the expansion of the universe, while the 'Big Bang theory' describes the entire history of the universe and its future fate.

Vosje wrote:We know that the expansion of the universe is accelerating and so the expansion of the universe must be going on faster now than it did when the big bang started.

A small correction here: the expansion of the universe depends on two competing factors: matter (both dark and baryonic) and dark energy. The matter content of the universe slows down the expansion, while the dark energy accelerates it. In the early universe, the density of matter was higher than that of dark energy. The consequence is that the expansion rate of the universe started very high, and gradually declined during the first few billion years, due to the matter content. However, the density of matter keeps decreasing, while the density of dark energy remains constant (according to the standard model). Therefore, dark energy has now become the dominant factor, and the expansion rate has changed from a deceleration into an acceleration.

The standard model is sketched in this figure, as the long-dashed curve:

hackenslash wrote:I would normally say that the bang is still going on, but this is less than uncontroversial, not least because we're in a period of accelerated inflation, so while it can be said to be still happening, there is slightly more to it than that because of the added impetus.

I wouldn't use the term 'inflation' for the current acceleration. Inflation refers to an hypothetical extreme expansion during the first fractions of a second, rather than the 'normal' expansion over billions of years.

Yeah, I suppose I'd use "Big Bang" for the event that started off our inflating patch, or for the first few gazillionths of a second's worth of the expansion. There's been a significant shift from particle physics towards cosmology in recent times hasn't there ?

Pulsar wrote:

hackenslash wrote:I would normally say that the bang is still going on, but this is less than uncontroversial, not least because we're in a period of accelerated inflation, so while it can be said to be still happening, there is slightly more to it than that because of the added impetus.

I wouldn't use the term 'inflation' for the current acceleration. Inflation refers to an hypothetical extreme expansion during the first fractions of a second, rather than the 'normal' expansion over billions of years.

Agreed. A linguistic slip on my part.

twistor59 wrote:

hackenslash wrote:I would normally say that the bang is still going on, but this is less than uncontroversial, not least because we're in a period of accelerated inflation, so while it can be said to be still happening, there is slightly more to it than that because of the added impetus.

Nah it finished long ago. Isn't 30s the average time for a bang ?.... oh....wait....

Okay, now I don't feel quite so bad about my post in this thread...I'm not the only one that couldn't resist it...

BlackBart wrote:Wasn't 'Big Bang' a disparaging description coined by Fred Hoyle? It was never meant to be descriptive of any of the mechanisms involved in the first place.

Yep.