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The bullet thing.


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what do you research steve? i am intrigued to know

best wishes

Paul

I can't tell you or I would have to kill you. I work for a Government sponsored organisation which carries out research into nanomaterials and then utilises these findings to assist UK industry in commercialising high technology products. These cover many fields from military to medical applications. My own personal research looks into surface interactions at the molecular level which has very diverse applications from stealth properties to stay-clean clothing.

Sorry I can't be more specific.

Steve..

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Would I be correct if I were to say that Physicists look upon the Universe the same way as we look upon the earth, where we live on the skin of the Earth and do not notice the curvature much the same way as we do not notice the curvature of the Universe on a much larger scale? So when we think we are moving in straight lines here on Earth we actually follow the curvature of the Earth. Is that the gist of things?

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Right, I see it a bit clearer now. If I fired my bullet straight up it can only ever follow the curvature of the Universe in any direction. So the Universe is slightly curved on a super massive scale. OK, if the Universe is so big and so massive why doesn't the mass of one side of the Universe effect the direction in which light travels at the other side like a super massive black hole effects light?

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The effect you are talking about would only come into effect if there was a 'bipolar' distribution of matter. Paul can probably answer this one better than me but I think that the matter distribution throughout what we know is sufficiently well distributed to stop this happening. You do see it on a smaller scale though with gravity lensing around groups of galaxies, it has even been recorded around our own sun during an eclipse, but I think the scenario you propose is probably a bit too extreme.

Steve..

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You hear all different points of view on the size etc of the universe, some quote the ever expanding universe, How can it be expanding if it's already there? otherwise there must be an end to it, and if this is so whats after its end.

Jeff.

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Absolutely. The bullet follwow the curvature of space. This path is technically called a geodesic. The shortest path through a curved space.

Cosmology is built on the principle of Isotropy and Homogeniety. This means that the universe is the same everywhere and in all directions.

On our view point this statements is a load of carp, the universe is not the same everywhere. And this is correct.

But on the largest scales, the universe appears to be the same in all directions. Implying that the matter distribution looks more even on large scales. Two points on opposites sides of the universe are separated by twice the age of the universe..around 28 billion years. So gravitational signals havent had long enough to traverse the diameter of the universe, so they cannot be influenced by each other...i think.

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The effect you are talking about would only come into effect if there was a 'bipolar' distribution of matter. Paul can probably answer this one better than me but I think that the matter distribution throughout what we know is sufficiently well distributed to stop this happening. You do see it on a smaller scale though with gravity lensing around groups of galaxies, it has even been recorded around our own sun during an eclipse, but I think the scenario you propose is probably a bit too extreme.

Steve..

Thanks for that. The distribition of matter throughout the Universe, is it even so that we can witness a enertia effect from the big bang?

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Indeed, hubble proved in the 1920's that the universe is expanding. Measurements made by hubble space telescope of distant type 1a supernovae have suggested that this expansion is accelerating..its running away. The explanation for this is dark energy. A magic repulsion force driving the expansion. This dark energy represents the lack of understanding in this field of cosmology.

In 1915 einsein published the General Theory of relativity...an extension to the special theory published in 1905 to include gravitational accelerations. When einstein looked at his equations he found that they predicted the universe was expanding. But einstein didnt believe in an expanding universe, and altered the theory slighly to make sure the universe was static. In doing so he had to add a Constant, labelled Lambda..the cosmological constant. Static universes are inherently unstable, as small pertubation will cause an eventual collapse. So einstein added a small repulsion term to halt any collapse. he had made a static stable universe.

Around 10 years later Hubble proved this wrong..the universe was expanding, just as einstein had predicted. Einstein called this 'the biggest blunder of his career.'

But it turns out that the universe may really have a cosmological constant...dark energy, driving the expansion

So the universe may indeed be ever expanding. Some hope that gravity will win and halt the expansion and cause a 'big crunch'

Unfortunately, there is far too little mass for this too happen. This is another problem in astronomy...dark matter. More is known about this.

The future of the universe looks bleak. It will accelerate forever perhaps, always cooling, and all the stars will die...a cold dark death for such a wonderful thing, seems almost cruel.

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But if the Universe is equal in every direction, how do we explain voids of 100 million light years without any visable matter then clusters of Galaxies in a compact region? That would surely suggest an unequal distribution of matter and the lack of enertia from a central point?

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The effect you are talking about would only come into effect if there was a 'bipolar' distribution of matter. Paul can probably answer this one better than me but I think that the matter distribution throughout what we know is sufficiently well distributed to stop this happening. You do see it on a smaller scale though with gravity lensing around groups of galaxies, it has even been recorded around our own sun during an eclipse, but I think the scenario you propose is probably a bit too extreme.

Steve..

Thanks for that. The distribition of matter throughout the Universe, is it even so that we can witness a enertia effect from the big bang?

I think I know where your coming from on this one. I guess the big bang would have sent 'matter' in all directions. This matter of course evolved through time as it moved away. You had the initial Planck Era, physicists still don't understand this era, then after 10^-35 seconds after the big bang, the inflation era started, and the 'known universe' expanded to 10m in size, we then had the quarck era (at 10^-32 seconds) where quarcks and other exotic particles such as gluons appeared (size 100km), then at 1 nanosecond after the big bang, we have the separation of the electroweak forces i.e the forces of nature started, this goes on through several stages until after 100 seconds after the big bang where we have the nucleosynthesis era where neutron gradually convert to protons as the universe cooled (now 10 light years across after 150 seconds), then finally after a few more stages after 300,000 years we have the start of the matter era where the universe was a 100 million light years across.

How do we know all this, computer simulation. After time though as stars then galaxies form, gravitational forces then started to 'pull' on close by galaxies causing them to move together, hence we get clusters of galaxies such as the virgo cluster and our own local group, which is why although the universe is expanding our own galaxy and the andromeda galaxy will collide in several billion years time, so gravity has pulled the random pattern you may have suspected following the big bang to give the distributed nature of the universe today.

Paul mentioned dark matter in a previous post, the simplified version of events above doesn't even take this into account.

Steve..

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there universe is anisotropic on 100Mlyr scales, but on scales of 1 Glyr things smooth out. But the principle is isotropy is counter intuitive. Its almost unbelievable

My question regarded the distribution of matter throughout the Universe. If the Universe is Isotropical the distrubition of matter would appear much, much more uniform that it appears at it's current form surely?

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I think you have been made the victim of when physicists don't fully understand something they tell you its counter intuitive or just because it does, I know, I do it to people myself I guess over these very large scales that Paul is talking about (i.e 1Glyr), the density of particles is pretty even and so isotropic, but on smaller scales i.e where I was trying to come from when explaining how the matter formed and evolved in the first place, it is certainly anisotropic, which Paul has already pointed out.

Another problem is estimating the distribution of matter in the universe, we can't map all of it directly and accurately as it takes so long for the light from these distant structures to reach us, they've had billions of years of evolution since that point but we can (and have) made estimations to there current wherabouts in the cosmos. There are too many uncertain variables to be able to give you a totally definitive textbook answer imo (another way scientists put people off).

Steve..

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If you wound the Universe backwards in time like a slow motion explosion on Earth similar to videotape reversed until you found the epicentre of the explosion there would be several fundamental differences between the two respective examples. On Earth when there is an explosion, the matter if all forces are equal in all directions, is distributed evenly in concentric circles around the explosion. If this happened in the big bang then matter would be distributed evenly throughout the Universe in similar concentric circles. This is not the case because I have been reading about it. Infact it is far from the case and the matter is distributed at an almost impossible pattern to be able to reverse the tape of creation and end up with all the matter in the same place or singularity. Is the big bang theory a load of rubbish then or what?

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And i would go futher to say that when I look through a telescope at Galaxies from my back garden, I get the strange feeling that I am seeing creation in my midst. My gut feeling is that the big bang stuff is somehow incorrect and that Galaxies are born into this Universe and absolutely don't know each other from Adam. I may be wrong but thats how it looks through a telescope to me.

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Kpax IMO you are trying to over simplify things with your analogies again, your explosions are subject to many forces which did not exist at the time of the big bang such as friction and gravity so you cannot compare the two like for like. I have already tried to explain, at great length, about matter formation and its subsequent distribution throughout the universe and how this has developed over 14 billion years. You may be right, the big bang may be completely wrong, but it is what we have that fits the evidence at the moment. One of my previous posts in this topic mentioned the Planck Era, the laws of Physics as we know today do not explain what happened at this point.

I think most of us share your feelings when we look through a telescope and it is very comendable that it ignites questions that you feel the urge to answer, this is human nature, and the day this stops will be a very sad day indeed. Cosmology is a tricky subject though, it is the realm of the mathmaticians and theorists who fit theories around the evidence, on the whole they are probably right and our knowledge grows day by day, but there is so much we still don't know and discovering these gaps in our knowledge will help us refine these theories and evolve as a race. Just take our own moon for example. A number of recent craft, observations and resampling of lunar rocks has revealed many things hitherto unknown about our companion. We live in exciting times.

Take a look at http://star-www.dur.ac.uk/~csf/homepage/Links.html, Prof Carlos Frenk's homepages for more detail on matter distribution and trying to understand the big bang.

Steve..

Steve..

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Kpax, the big bang is wrong!..at least partly.

The Big bang cannot actually explain the finer points of our current observations. The WMAP probe mentioned earliier, was launched to record the photons emitted from the promordial universe, some 380,000 years after the big bang. Before this age, the universe was too hot for electrons to orbit the positively charged nuclei. The free electron gas, if you like, is an excellent scaterrer of photons. No photons escaped, so the universe at this point is called opaque. After 380,000 years, the electrons could combine to form neutral atoms, which are fairly useless at scattering photons. The universe is now transparent to radiation. It is this 'burst of light' that WMAP ws sent to collect. This period is called recombination. After travelling through the expanding space, the photons are now at microwave wavelengths

What WMAP saw was quite incredible...an almost perfectly uniform distribution of photons. Patches of sky from one side of the universe looked exactly like patches of sky from the other, even though the areas of sky hadnt had time to interact to create this smoothness. The universe wasnt old enough.

So how do we explain the almost uniform distribution of matter that WMAP saw.. (looking back a distance of 13.6 billion years)

The big bang cant. At least not in its current formulation.

In the 1960/70's, a particle physicist (Alan guth) working at MIT thought he had found the answer. He said that actually, the seemingly disconnected parts of the sky, actualy were connected, touching, inteacting, when the universe was still only a fraction of a second old. For this to be true, the universe had to undergo a period of rapid expansion...this is called Inflation.

I dont know a whole lot about inflation, but it sorts out one or two other discrepancies in the original big bang theory.

By simply including a period of hyper expansion into the original big bang theory, we can explain most of what we see. It is now clear why WMAP sees an almost uniform universe...

I said almost uniform. WMAP is really a thermometer, recording the temperature of this background radiation (2.7K). There are fluctuations on small scales. These fluctuations are of the order 10^-5K. They represent areas where the universe was slightly denser than other parts. The density fluctuations accreted matter through its stronger gravity. From the tiny seeds, might galaxies grew. Indeed, the density fluctuations witnessed by WMAP correspond to the pattern of galaxies observed by the like of the HST.

So on the scale that WMAP observed, the universe really is isotropic..but probably only on those scales.

Alan Guth came before COBE (WMAP's predecessor) and WMAP, I wasnt stating this in chronological order. Its the way I understand it.

Hope this helps

paul

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In a big bang without this rapid inflation, what are now widely spaced regions of the universe could not have achieved the similar densities and temperatures. In fact, inflation theory proposes that our observable universe is derived from a tiny homogeneous patch of the original universe. To use a popular analogy for this one the effrect of inflation is like expanding a wrinkled sphere, after the expansion the sphere gets smoother and smoother, becomes very smooth and ultimately becomes extremely smooth and flat which is the situation we see today. There is strongf evidence for the big bang:

Background radiation - the spectrum of the CMBR

Expansion - if the universe is expanding and cooling, we can thus suppose that it was once smaller and hotter

Balance of elements - the theory exactly predicts the proportion of light elements (hydrogen, helium and lithium)

General relativity - at a basic level this theory states the universe must be expanding or contracting, it casnnot stay the same size

Dark night sky - Olbers paradox can be explained by the big bang by the supersition that the universe has not always existed.

I think these simplified points serve to strengthen what Paul and myself has said already in this post. The reason we use low energy photons of the cosmic microwave background radiation (CMBR), (measured as Paul said with the WMAP satellite) is that due to the expansion of the universe, the wavelength of the radiation emitted by the early universe has been stretched by a factor of about 1000, so the photons reach the satellite/earth not as photons of light but as low energy photons of CMBR.

Steve..

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Thanks for these explanations Steve and Paul. I'm certainly not a maths person and most stuff concerning maths is out of my understanding being honest.

I'm trying to understand the Universe by looking at it through my scope and I watched the series 'the Universe' on the History channel.

My problem is, I look through my scope and I see a shape where all the Stars and Gallaxies are sat amongst each other in a 3-d invironment. Which ever direction I look it seems to be the same sort of shape so I can't seem to envisage this flatness shape which has been mentioned. If someone could perhaps sketch the shape for me then I might understand more. I understand that all the Gallaxies are moving apart at a certain speed like in the Hubble constant and I can invisage this. It's the flat thing which confuses me. How flat are we talking? Is it flat as in a thin rubber sheet, but the thickness of the rubber sheet might be 1 billion light years thick. If it's thin with no 'z' axis at all, how do we fit the Earth in the thiness?

Thanks ..kpax

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i am sure...i think, that this surface of the balloon must be 3d. According to measurements made by WMAP, and other probes, the value of the curvature K is very close to zero. It appears flat over a very large scale, but may have a small curvature on the biggest of scale...

the problem of trying to envisage this, is that the human brain is trying to think in a 4d way...how can a surface have 3dimensions? unfortunately th human brain has been incorrectly engineered, and cannot even imagine a 4th dimension...

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