h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"The most beautiful thing we can experience is the mysterious. It is the source of all true art and science."

"The important thing is not to stop questioning."

Two quotes I live my life by. They are by the greatest mind of the 20th century - Albert Einstein.

Now I've read a number of articles about the "Big Bang" theory. I am aware of the proposed doppler effect. However I am not sure why this is taken as the accepted norm.

Admittedly, I am not an expert - I simply haven't got that kind of time. But like to think my knowledge and interest covers a lot of fields.

Before you start I'm afraid I haven't got time to read long articles from other web-sites about the "big bang" theory. Sorry, I'm very busy at the moment.

But I am curious about the subject.

Can anyone tell me why they believe in the "Big Bang" Theory?

Because it is the current hypothesis accepted as the most likely explination in light of the eveidence 'we' have at the moment, by teh majority of 'experts' in teh field...

If there was proof then it would no longer be a theory

Doppler is real. Doppler radar will tell you the speed something is travelling at.

Considering that in space there is a vaccum, and at the point of the Big Bang there was nothing, surely there was no bang at all until a split second after the event.

Also, as there was no one there to hear it , there would have been no noise anyway.

When they discovered that the universe was expanding, they came up with two theories to explain it: one was that was continuous with new matter being created to fill the gaps, and one that there was a single 'explosion' from which the entire universe came. One of the predictions of the explosion theory was that things should have been going faster in the past and are slowing down. Looking back into the past, they found that this is the case, so it supports the Big Bang and the other theory was dropped. Until anybody comes up with an even better theory, the Big Bang is the best one around. It has been refined by the Cosmologists so that they know exactly how it happened right back as far as a split second after the bang.

I went to a lecture at UCD recently, where a guy was trying to say why creationism cosmology was wrong. So he also had something against the Big Bang. Although his arguments seemed no better than what has been said many times before by creationists. Like the cause and effect part.

When a theory is proposed it is not enough for it to explain all current phenomena for it to be accepted. It must propose at least two further "proofs" before the scientific community will take it seriously, Einstein actually proposed three for general relativity. In the case of the Big Bang one of the proofs was the idea of background radiation left over from its origin, this has been found and has increased its acceptance.

The doppler shift effect seen when observing all astral bodies pushes the light we recieve from them toward the red, this means that everything's moving away from us (and everything else) which points to there being, at some point in time, a singularity - a starting point, where everything is moving out from.


So the theory goes.


Don't forget, it's night on impossible to prove that something is, it's quite easy to show that something isn't - that's what people find most disturbing about science

Hi Vercingetorix,

I'll tell you what I know, which is not that much really.

First of all, the Doppler effect is not just a theory, it is a mathematically provable fact. When a generator of a wave (such as an ambulance) is approaching you at speed, it will have a higher pitch than it's "real" pitch, and when it is travelling away from you, it will have a lower pitch.

The same is true for stars, where the light they emit will be shifted to lower frequencies ("red shifted") if they are moving away from you. This is what has been observed by scientists (and many amateur observers, I imagine) for quite a long time - very distant objects tend to have very high red shifts. This means that all faraway objects are moving away from us at an enormous rate. The conclusion is therefore that the universe is expanding.

Also, objects very far away from us are moving away from us at a speed approaching the speed of light (This can be read directly from the red-shifts of these objects). The speed of light has been proven to be constant from many detailed experiments made over the past century.

This is interesting stuff because if a very bright event happened a long time ago, and you were moving away from it at a speed approaching the speed of light, it would look as if it were frozen in time. You can literally see back to the origins of the universe, by looking through a telescope that is strong enough.

Also, as far as people know, there appears to be a correlation between the distance an object is away from us, and its speed away from us. So, if it has a very high red shift, then it is a long long way away, and if you know how big the red shift is, then you can read off its distance away from us.

So, I guess there is a lot of data out there: snapshots of the early universe, distances and speeds of objects a long way away, the times light left the stars, plus some dimensions and particular events, such as supernovae, that help to provide some extra information about the movement of the object through space.

Pack all this into a computer, and you might just be able to get a picture as to how all these objects have moved over the aeons. And this is what astrophysicists have done I guess, leading them to conclude that a big bang origin is probable. (I have never seen anything definitive on this subject).

There is also the alternative theoretical approach that says "say there was a big bang, then, if so, what would happen?" Well, as I understand it, it so happens that a coherent model has been created that explains how atoms, matter, stars and galaxies would be formed. It also goes on to
say that an enormous amount of microwave radiation would be released, and that it would be possible to detect this radiation with suitable radio telescopes and microwave detectors. Scientists figured this out some time before suitable detectors were available, and when they went looking for evidence of background microwave radiation, they found it in abundance. Evidence to them that the big bang theory was essentially correct.

Woodpigeon

BTW - it's said the snow you see on your TV screen when there's no signal is the self same background radiation

That`s a different kind of background radiation. Though I suppose a small part of it might also be left overs from Big Bang. But other than that it is natural EM-sources.

One question about the big bang is where is all the anti-matter? As far as we know about particle physics, when creating matter from energy you should get equal amounts of matter and anti-matter. But if you look out in the universe there doesn`t seem to be any signs of anti-matter. Which is probably good, cos it could annihilate the entire universe.

Some also say that if the universe is 15-12 billions years old, the galaxies shouldn`t have had time to form. Perhaps the expansion is not an explosion, but more a kind of pulsating movement.

The COBE Map project used temperature anisotropies to help plot mass distribution in the dissent past and thus gain important evidence in favour of the "Big Bang" theory.

http://lambda.gsfc.nasa.gov/product/cobe/

Evidence for the big bang:

The galactic red shift: Distant galaxies show a redward shift in spectral lines. It is proposed that this is caused by the doppler effect - which means that the galaxies are moving away from us. The speed of resession is proprtional to their distance from us. Such a phenomenon is most easily explained by all galaxies moving away from each other. If that is the case they must, at some time in the past, have all been very, very close to each other.

Cosmic background radiation: When the universe was very, very small it would have been very, very hot. As it expanded this heat would have been spread out over a larger volume - which would have cooled the universe. Hot objects emit electromagnetic radiation - the hotter they are the shorter the wavelength. That's why a hot poker glows red - as it cooles it emits infra-red, then microwave radiation. It was calculated that the universe should have cooled enough to emit radiation indicative of a temperature of 2 to 5 degrees above absolute zero. When they went looking for this radiation they found it.

Abundances of light elements: Very old stars consist almost totally of hydrogen and helium with a bit of deuterium and lithium thrown in. So these elements must have been present when the oldest stars formed. To make the elements apart from hydrogen needs certain conditions. These conditions are those proposed by the hot big bang model.

I don`t get that last one. The heavier elements are supposed to have been made inside stars. And yes that probably means there was a lot of hydrogen to begin with. But that doesn`t mean the cause was necessarily Big Bang. For example the Steady State theory could probably explain that as well.

And the COBE experiment, I heard that the heat differences found were actually within the error-margins of the instruments, so not all that useful.

And since everything supposedly goes towards disorder, the universe must have been completely ordered to begin with. How would that look, I can`t quite imagine that.

If you don't have time to read the articles, it seems to me you don't have time to get useful knowledge about anything or do your homework. Consequently, you flunk astrophysics 101. Try again next semester.

Free advice is worth every penny.

All the really heavy elements are formed within the cores of stars. When these stars explode material from their cores is spread throughout sapce and is used as the starting material for the next generation of stars.

If the BB theory is correct there should be a first generation of stars that formed from the material created in the big bang. The BB theory predicts a range of proportions of elements that were formed in the early stages of the universe. It turns out that the early universe was mainly hydrogen, a fair chunk of helium and a smidgen of lithium - nothing else, no heavier elements. The theory also predicts the abundancies of the different isotopes of these elements.

When we look at the compositions of really old stars we find that it's a very good match to the predicted compositition of the early universe.

This is something that's not easy to explain in a steady-state universe. Why should old stars differ in composition from young stars? If the interstellar material, from which stars are born, has an unchanging composition (which would be a requirement of the SS theory) then stars of all ages should also have the same composition. And they don't.

The COBE data that you're thinking of was measuring diferences in the temperature of the background radiation. These differences were very close to the noise. But the background radiation itself is definitely there. It's very easy to measure it.

Yes, but wether there are any differences seem to be very important as well. If the universe was homogenous you would expect it to never get any structures such as galaxies and stars.