[krisp (OP)]

what is the big bang theory based on? and has anybody ever actually seen an atom?

[graham.d]

The big bang theory was based initially on the discovery by Edwin Hubble that distant galaxies and clusters of galaxies are moving away from us and that the further away they are, the faster they are receding. The relationship is such that it is possible to extrapolate back in time to suggest that it all started about 14 billion years ago. There are other possible reasons for this relationship because the way we measure the speed is by the amount of Doppler shift in the wavelengths of the light and radio waves we can detect and this could be due to other effects outside our knowledge. However there has been other corroborating eveidence and, in particular, the Microwave Background Radiation which is a very uniform temperature wherever one looks. This correlates very well with there being a very hot, dense phase in the universe. Many models have been built up that show how the universe may have developed based on the idea of a Big Bang concept, and these are consistent with observation.

You can see atoms with an electron microscope. I am sure you will find images on the web. You can see how atoms form into crystals, for example: you can't see any substructure so they look like loads of regularly packed spheres.

[Bored chemist]

Single atoms are tricky, but single molecules are now just about in the realms of analytical chemistry.
(of course, ther's the fact that a single crystal of a covalent compound is a single molecule- but that's not what I mean).

You can under certain conditions, observe fluorescence from a single molecule.
Not quite the same as "seeing" it- but close.
Scanning tunnelling microscopes and atomic force microscopes are more like reading Braille than seeing, but they will let you image single atoms and molecules.

[krisp (OP)]

thanks for that. bbk

[flr]

 But it is still possible that the "big-bang" is actually infinite in the past?

[krisp (OP)]

The big bang theory was based initially on the discovery by Edwin Hubble that distant galaxies and clusters of galaxies are moving away from us and that the further away they are, the faster they are receding. The relationship is such that it is possible to extrapolate back in time to suggest that it all started about 14 billion years ago.                                                                                                          ok i have been thinking about this and if the universe is expanding and we (earth) are part of the universe why can we observe other galaxies moving away? has anyone found where it is expanding from?and have we checked futher and other sides of space to see if the speed is increasing?   

[PhysBang]

The big bang theory was based initially on the discovery by Edwin Hubble that distant galaxies and clusters of galaxies are moving away from us and that the further away they are, the faster they are receding.

The basic ideas predate Hubble's discovery, which is why Hubble refers to them in his initial publication.

ok i have been thinking about this and if the universe is expanding and we (earth) are part of the universe why can we observe other galaxies moving away?

The universe is expanding only in the sense that the average distance between galaxies is getting larger. There is no increase within galaxies because the gravity between parts of galaxies keeps things together. There is no expansion from any place, nor is there any expansion to any place.

[krisp (OP)]

( The universe is expanding only in the sense that the average distance between galaxies is getting larger. There is no increase within galaxies because the gravity between parts of galaxies keeps things together. There is no expansion from any place, nor is there any expansion to any place.)                                                                                                                                                                                                have we measured space, so how can we say it is expanding. if the only evidence is relative to the earth therefore we are not observing all of space. if the galaxies futher away are expanding quicker why cant we find the location of the big bang and there seems to be no other evidence apart from these expanding galaxies to justify the big bang.   

[krisp (OP)]

i missed have* at the start of my statement

[PhysBang]

have we measured space, so how can we say it is expanding. if the only evidence is relative to the earth therefore we are not observing all of space.

While it is true that all that we look at is from our own vantage point, if our vantage point is special, then we must be the centre of some sort of explosion. There is no scientific hypothesis that can explain this. However, if we assume that all galaxies see the same expansion, then we have a means of explaining this.

if the galaxies futher away are expanding quicker why cant we find the location of the big bang

Because there was no Big Bang event. The name "Big Bang" was created by an opponent of the theory; actual cosmologists who believe in the theory do not necessarily believe that there was some first event, they believe that the universe is expanding and that in the past it was extremely dense. Whether or not there was a first event, the expansion has no centre because the expansion of space is uniform: every place is expanding, unless gravity at a specific area (or molecular bonds) keep the objects there from drifting apart.

and there seems to be no other evidence apart from these expanding galaxies to justify the big bang. 

Except that there is a ton of other evidence. One piece of evidence is that the relative amounts of light elements in the universe is evidence that there was a hot, dense early universe where certain nuclear processes took place. There is also the way that galaxies are distributed. There is also the background radiation that seems to have originated in the hot, dense past. There is also specific details about this background radiation that make it fit the Big Bang theory better than any other theory.

[Robro]

It seems, from our perspective, that what we can see of the universe puts us almost right in the center of the visual sphere. Beings in the farthest galaxy directly to our celestial North could not even see the farthest galaxy directly to our celestial South, they would see the universe in much the same way we do as if they were in the center, right? The density of matter is based on what we can detect from within this sphere. So it seems that the universe could possibly go on forever in all directions. If redshift is the result of expansion, and expansion is reaching the speed of light at the edge of what we can see, then somewhere in the universe there should be a big rip already happening, right? I mean, way out there where the relative accelerating expansion from us is trillions and trillions times the speed of light, and then does this multiplier reach infinity? I wonder what is really happening out there?

[graham.d]

The theoretically observable universe is reckoned to be about 46 billion light years away to its edge but the universe could be much bigger. Some theories have the universe 10^26 times bigger!! It could also be smaller with us potentially observing the same distant galaxies in a variety of directions and at different epochs.

Beyond the edge of the observable universe there can be no causal connection with us so whatever happens there is irrelevent (I think).

[Robro]

So, in this sense, would the observable universe behave as an inverted sphere, or a sort of mobious loop? Has there been any observations in the cosmos of two images of the same thing in opposite directions from our perspective?