The big bang theory

Anything to do with the big bang theory is welcome here!

but if you don't believe in big bang do you then have an explanaiton how it all start zug

good answer but i said believe coz i didn't know how to phrase this another way coz i don't read astronomy in english coz it's not mt first language there for my vocbulaty about astronomy in english is really weak

Zug wrote:

By the way, George, you might want to change the title of this thread.  Big Bands are for music!

 Actually, Mike, it was Calum who created this thread.  I guess he would have to be the one to change it.

sorry, how do I do that :S?

Zug wrote:

In my opinion there was no "bang".  The Universe has been here for an infinite time, and will be here for an infinite time. 

Okay, all, have fun with that one.

If the Big Bang happened (the evidence says something like that happened) then time itself had a start. We have only had a finite amount of time since then so the universe hasn't existed for infinite time yet.

I have a bit of problem with infinite in any case. Although mathematicians seem happy to muck about with various infinities they are only actually happy when the infinity is potential rather than actual. In physics we don't even have the potential infinities to play with. If anyone says they have something that is infinite I will ask them how they measured it.

Sharukin wrote:

Zug wrote:

In my opinion there was no "bang".  The Universe has been here for an infinite time, and will be here for an infinite time. 

Okay, all, have fun with that one.

If the Big Bang happened (the evidence says something like that happened) then time itself had a start. We have only had a finite amount of time since then so the universe hasn't existed for infinite time yet.

I have a bit of problem with infinite in any case. Although mathematicians seem happy to muck about with various infinities they are only actually happy when the infinity is potential rather than actual. In physics we don't even have the potential infinities to play with. If anyone says they have something that is infinite I will ask them how they measured it.

 I like the idea on asking them how they measured it. Am I right in saying the evidence for the big bang theory is that they found pulses reflecting back to machines they have and this tells them that the universe is expanding.

If they found that the universe is expanding then surely everything had to come from one centre point and scientists believe that that one centre point was the size of a pinhead, which was holding everything we see around us. Amazing isn't it!

One question though, if the universe is expanding then in 100 trillion years, will we not be able to see anything in the sky; no stars, planets. 

As far as I can remember from my relativity and cosmology classes many years ago the redshifts (and blue shifts) of local galaxies are Doppler shifts but the redshifts of galaxies further away are not thought to be Doppler in nature. As I recall it is linked to the expansion of space and is therefore relativistic rather than Doppler so most of the redshift is not Doppler in origin and could be described as intrinsic to the structure of spacetime.

Am I a proponent of the Big bang Theory? Not really. I will happily agree that the evidence from redshifts to CMBR supports the Big Bang Theory but will then point out the incredible contortions required to keep the thing alive. Inflation, cold dark matter, dark energy, what next, magic?

So what to replace BBT with? I don't like the string theory/brane theory ideas because so far they are just pure mathematics and not really science. So what do you think then Zug?

I am inclined to think that the question of an origin for the universe is meaningless. If some kind of big bang or ekpyrotic universe is envisaged then time is born with the rest of the universe (it is spacetime after all) and what happened before is simply meaningless. No time, no before.

If the universe is thought to be never ending and never beginning then the origin is also meaningless, no beginning implies no origin. I can't say I am overly fond of the various steady state theories that have been propounded over the years, I think I have an allergy to the infinities that those let loose.

So, no origin for the universe. To be honest, the origin (or lack of it) of the universe doesn't really concern me much. I am much more interested in describing the way the universe works rather than trying to divine how whatever exists beyond the universe works. The evidence, whether experimental or observational, currently only tells us about this four dimensional universe.

I'm still new but I am very interested in astronomy and the big bang theory

Steady state theory hasn't been followed for many years. Background radiation from the big bang is the starting point for its evidence.

Sharukin wrote:

If anyone says they have something that is infinite I will ask them how they measured it.

Sharukin, Infinity can be measured, and is measured frequently.  In mathematics the entire point of Integrals is to measure the infinite.  Mathematicians will also tell you that some infinities not only can be measured but that some infinities are much greater than others.

Halton Arp looks like a crank to me.

I don't think that inflation, dark matter, or dark energy are contortions required to keep the big bang theory alive. I would say they are predictions of the theory. There is a growing body of evidence for the existence of dark matter and dark energy, and I think this supports the big bang theory, rather than weakening it.

De-Lar wrote:

Sharukin wrote:

If anyone says they have something that is infinite I will ask them how they measured it.

Sharukin, Infinity can be measured, and is measured frequently.  In mathematics the entire point of Integrals is to measure the infinite.  Mathematicians will also tell you that some infinities not only can be measured but that some infinities are much greater than others.

Integrals use infinite quantities as limits but this does not mean that anything infinite is ever reached or actually measured. If you measured an infinite quantity it would no longer be infinite, you could add a very small quantity to it and get something slightly bigger but still finite.

As I recall the various sizes of infinity contributed to Cantor's mental illness. Actually, I am happy to play with the infinite when I have my mathematician's hat on. However, mathematics deals with abstract objects rather than the very real physical objects that I have to deal with when I am playing astronomer. There isn't a lot more real and physical than a whole universe.

what does QED mean? And maybe when I'm older you never know I might have something to do with astronomy talks! But when I'm older I always will and always have wanted to be an astronaut!

Kids always ask the best questions! One little girl asked me what the aurora sounds like, so I had to go find out for her. You learn as much as they do that's the beauty!

My problem withh infinity is quite simple, you can never reach it so you can never actually show that it exists. The example of counting only proves you can always find a bigger number it doesn't actually show us anything infinite. Now, I know infinity gets used as a limit in mathematics but that is just an invented infinity, one of many mathematical objects that has no real existence. One might as well use n, the smallest number that makes you boggle (anyone know where that comes from?) as a limit. For a view on infinity that does not accord with mainstream mathematics try "Ad Infinitum" by Brian Rotman. If someone tells me that something real and physical is infinite I ask for some evidence. It has never been forthcoming so far.

I sometimes get asked about the size of the universe and the usual discussion of infinity ensues. I generally find that people confuse "endless" with "infinite". Once the discussion has got the point where we agree that there may be no end to space I ask if that means it is infinite. I generally get told of course it does. I then ask what would happen if the Earth were smoothed off to a perfect sphere. Could you walk around it without ever hitting a barrier? Yes comes the reply. So, is the Earth infinite? Of course it isn't. Gets the concept of endless but not infinite across quite nicely. Getting people to imagine a four dimensional sphere is a bit harder.

I think it is unlikely that the standard theory of gravity breaks down at large scales. Of the attempts that have been made to modify the theory of gravity in such a way, none have been entirely satisfactory. Astronomers have considered the possibility that gravity might be variable on large scales, but observations do not support this theory. Dark matter on the other hand is gaining more and more support from observation.

Halton Arp's theory rests on observations of objects which are close together in the sky, but which have greatly different redshifts. If these objects were to actually be close together in space then this would be evidence against an expanding universe and big bang. He argues that redshift is related to age, not distance. The weight of observations simply do not support this theory, and it is far more likely that although close together in the sky the higher redshift objects is a lot further away. By sticking to his theory despite evidence to the contrary, Arp has placed himself outside of mainstream science. In his articles he makes disparaging remarks about the mainstream astronomers who have rejected his theories. I think that's a little cranky.

ck516, what do aurora sound like?  I was intrigued by this a little while back but the best I could find was this,

http://www.northern-lights.no/english/what/sounds.shtml

I'm moving north so with any luck I should get to experience an aurora myself fairly soon.

I am not going to wade too deeply to this one because things get argumentative. I will however through these ideas up for discussion.

If you want to be crass and you rightfully believe in the big bang then the diameter of the universe has a maximum length of 2 x c x time since big bang. This rather obviously isn’t infinite at all!

What does the universe expand in to? This could be infinite! (This is more rhetorical than a genuine question!)

If you don’t believe in the big bang then you will never be happy. Steady state theory was disproven a long time ago and to bring it up again shows peoples desperation to not accept what is staring them strait in the eyes!

I don’t think that you are looking at an example of infinity here!  

This will I am sure amuse you all as a concept: Imagine a circle and from its centre it can have an infinite amount of spokes going out to the circumference. Imagine a greater circle is drawn around the smaller. If you extend the spokes out from the smaller you have gaps between them when they reach the larger circle’s circumference! Thus the greater circle has a greater infinity. This was studied greatly in Europe in the 19 hundreds and was dropped as many of the mathematicians who studied it became mentally ill! The basic fact remains that infinity isn’t a constant.