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

If there was a Big Bang, and the universe is expanding, am I being naive in thinking that astronomers should be able to trace the movement of everything in the universe back to that one point, and so discover the centre (and possibly even the age) of the universe? If they can, why haven't they? I mean, it seems pretty obvious to me that if everything is flying outwards from an explosion, you should be able to work back to the point of origin. And if they have, why haven't we been told? Will they find Zaphod Beeblebrox's ego there?

There is an awful lot of stuff out there, and it has had an awful lot of time to interact with everything else. We cannot even follow asteroids that have an Earth crossing orbit, so as for the rest of everything, it is not likely. Some also think that a big chunk of the universe is in dark matter, but no one knows how much, or where most of it is. If you could see far enough you might be able to see it, but our sensors are no good enough yet. Just a few possible reasons, some of which may not be true (I know a bit, but not a lot about the subject Until later....
BCNU - Crescent

According to what I have read in Carl Sagan's 'Cosmos', all observable galaxies are receding away from each other. What is more, the more distant galaxies are moving FASTER than the nearer ones!!
They have not yet managed to find a point where all galaxies are receding equally, so origin of Big Bang cannot be deduced yet.

'G'

The thing about dark matter is that, well it's dark. This means it's not easy to detect. Astronomers have been arguing about dark matter for ages, well since someone suggested that there's all this mass we can't account for. The main thing about the search for dark matter is that how much of it there is will determine what happens to the universe - continue expanding forever, expand to a certain size and then do something else or whatever.

But wait, there's more. I'll have to go and double-check this to be certain, however, I'm pretty certain that there was some general concensus amongst cosmologists about a new concept called "inflation" it has all to do with exactly how the universe went about expanding in the seconds and nano-seconds after the Big Bang. To neatly paraphrase: Nothing exploded and then grew bigger. But it did this everywhere at once and not just at one point (the universe, encompassing 'everything and everywhere was by this time shooting out from the size of a electron to a grapefruit). It's true that everything is moving AWAY, backing up the idea of a point of origin, but it's not as simple as all that: Imagine drawing two dots onto a balloon with a felt pen. As you blow the balloon up so the surface area of the balloon increases and the dots move further apart from each other. From the perspective of either of the dots (assume they are planets in an inflating universe) they see the Universe racing away from them as if flung from a central point but it's actually the fabric of space, for want of better word, 'growing' between them. Consequently finding the point of origin were the universe began becomes increasing impossible as everything drifts slowly (actually quickly, but just over a very long time) apart.

Umm... right... ok. I see. I understand the balloon analogy. I just wish that I could comprehend the mechanics that make it possible for the universe to be in 3-D, and on a single plane both at the same time. Thanks for the reply, it was, er, helpful

Jim

If you think 3 dimensional thinking is difficult, try imagining 4 dimensional, that some cosmologists are trying to think in!!!!!!

'G'

I can sort of do that, well, I can concieve of it anyway. I was watching an Open University programme many years ago (how odd that that activity and the fashions of the presenters never got mentioned in the '70's' Guide Entry), and they explained all about an object called a Klein Bottle, which is a three dimensional version of a Moebius Band - that thing you get when you take a strip of paper, put a twist in it, and join the ends together so that you get on continuous surface from the two sides of the paper - 3 dimensions from 2.

To make a Klein Bottle, you do the same thing with a cylinder, which has two surfaces - inside and outside, and this is where it becomes just about impossible to explain in words, because you have to put a 'twist' in the cylinder and join the ends together, just as with the Moebius Band. The upshot of the process is that it can only exist in 4 dimensions decause it has to pass through itself.

There's an explanation here http://www.math.rochester.edu/misc/klein-bottle.html, an animation here http://www.geom.umn.edu/zoo/toptype/klein/standard/, and these people actually "make" and sell them (even ones that you can drink out of!) http://www.kleinbottle.com/. Well I never!

Scientists have worked out the age of the universe. It is 15 billion years (15,000,000,000) give or take 5 billion years. This is done by running the expansion in reverse and seeing when it collides.

Unfortunately, you can't do the same for where it all happened, as it involves a lot of thinking in 4 dimensions. The entire universe is expanding, and no one point can be considered at the centre.

The expansion of the Universe (and thereby, the Big Bang therory) is predicated on the Hubble Redshift. Hubble saw that the spectra from other galaxies were shifted towards the red (lower frequencies), and the more distant a given galaxy is from us, the more it's spectrum is shifted. He assumed that this is a Doppler effect, and to fit Doppler equations, these super-massive galaxies must be moving very fast indeed - quite near the speed of light; the farther ones moving even faster than the near ones.

I'm not so sure however. What if photons loose energy over time? Given that the speed of light in vacuum is constant, an energy loss must result in a lowering of the frequency of the light. The longer (and farther) a photon travels, the greater it's frequency shift.

If this is the case, then the Universe is not necessarily expanding. Granted, the distance to the nearby galaxies can be measured by the parallax method, using opposite points of the Earth's orbit as the baseline. Over time this can give us an idea about the relative movements of our nearest neighbors, but can we say 'Andromeda is moving away from us, therefor all galaxies are moving away from each other'?

Remember, we have been observing the Grand Cosmos for only two or three generations. Compared to the time and distance scales of the Universe, isn't that kinda like looking at one high-speed flash photo?

As for the original question of where is The Center Of The Universe? It is within the heart.

If everything is moving away from everything else, and the things further away are moving ever faster, does this not men that eventually these things will be far enough away and accelerating fast enough that they would travel faster than the speed of light? As that is impossible, when do they stop getting faster?

Am i making any sense or just being a naive school studant? help me here before my brain tries to think through one of those bottle things and explodes.....

Well, the Big Bangers say that there are two possibilities:

1) There is enough mass in the Universe that the Total Gravitational Force will be enough to eventually reverse the expansion. The Universe will begin to contract, everything finally coming back together to a singularity. At some point beyond that, there may or may not be another Big Bang.

2) There is not enough mass for the Total Gravitational Force to overcome the expansion. Things will just keep drifting apart, until all stars have burned out, and we entropy toward absolute zero.

The universe is expanding, but it is not accelerating. Quite the opposite. As the galaxies spread further apart, the gravity between them slows them down, so they are not expanding as fast now as they where a billion years ago. Whether the gravity will be enough to stop them entirely or not is an unknown question. Either it will, in which case eventually the galaxies will all head back towards each other and end in a dramatic Big Crunch, or more likely, it won't, in which case the universe will keep on expanding for ever.

Because all the universe is expanding, galaxies that are further away appear to be going faster. But since nothing can travel faster than light, the further ones just appear to get closer and closer to the speed of light, so at some humungous distance, they might be doing 99% of the speed of light relative to us. Further out, they might reach 99.9% of the speed of light.

This question confused me a lot when I was younger but the answer is actually quite simple.

The Big Bang happened everywhere simultaneously.

This might seem odd to some but the problem comes of thinking of space-time as this infinite empty thing which is already in place before the Big Bang introduces matter. From this perspective it is logical that there must be a point where it occurred, but the basic assumption that space-time was already there is wrong.

The Big Bang was not just the creation of energy & matter but was also THE CREATION OF SPACE-TIME ITSELF, i.e. there were no places until the Big Bang made them. With space-time expanding these newly-created 'places' are now much farther apart and are still moving apart. Please note that it is not the various galaxies themselves that are flying apart from one another, it is the space-time in which they 'sit' which expands and takes them along with it.



NOTE: The above is my understanding of the situation and I know it's a bit simplistic (e.g. there has been recent superstring speculation on the pre-Big Bang universe) but I can't be bothered to check it all out right now. Tell me off if I'm wrong

Huw, this sort of thing is pretty much beyond my comprehension, so I wouldn't presume to tell you off one way or the other, but thanks for the input. It's kinda hard to grasp the idea that there were no places and no time before the big bang - what can possibly be there when there's nothing there? I guess I'll just have to take the word of people who know more about it than I do, just like when my physics teacher said that when you suck liquid up a straw, the liquid is forced up the straw by atmospheric pressure pushing down on its surface, rather than you pulling it into your mouth with the action of sucking.

Sucking's easy.

The water in the straw is experiencing 2 forces (ignoring the straw itself).
A-the force pushing it down. This is made up of (1) gravity and (2) the molecules of air in your mouth banging against the top of the water.
B-the force pushing it up. This is caused by the molecules of water banging against the bottom of the water - the opposite of A(2).

(those molecules just can't stop dancing!)

Normally A is much bigger than B. ie. A(1)+A(2)>B

By sucking the air out of your mouth into your lungs you can reduce the force of A(2) to such an extent that A(2) is very small.
Suddenly, A(1)+A(2) is a lot smaller and becomes less than B.

The water comes out of the top into the emptier space of the mouth.

Alternatively:-
Think of it as a long train carriage with doors only at each end. When passengers outside are trying to get in at both ends nothing moves. However, if those outside one of the ends go elsewhere (to catch a bus, perhaps) the force of the passengers at the other end pushes everyone through the train.
So what you're doing by sucking is just emptying your mouth of air, letting the water flow in by itself due to pressure.


It's easier than space-time!

I personally don´t see any problem in understanding sucking in a straw. And I find space-time science quite interesting also. But I don´t see how you can claim that it´s not you sucking the straw. If what you just described isn´t you sucking up the water, then what would it take to make it you? To me it seems what you said is basically the definition of sucking in a straw.

Yes, I gave a loose description of how sucking things up a straw works.

I was merely expanding on the physics teacher's attempt to outline the processes involved. I was not denying that physics can suck.

Hey, I once considered becoming a physicist so :-p Anyways, what I didn´t understand was "when my physics teacher said that when you suck liquid up a straw, the liquid is forced up the straw by atmospheric pressure pushing down on its surface, rather than you pulling it into your mouth with the action of sucking. "
To me it seems those two things are the same. It´s like saying that things don´t fall down to Earth, they´re simply attracted by the gravitational pull. One of the things sound more scientific, but it´s the same anyway.

Hmmm, what have I gotten myself into here Let me try to explain it a little more clearly. When I suck on a straw, it feels like I'm physically pulling the liquid up the straw and into my mouth, sort of like hauling an object up on the end of a piece of rope. Then the teacher comes along and tells me that atmospheric pressure on the surface of the liquid is actually doing all the work, which I found hard to grasp. I don't doubt that what the teacher said was true because I (still) don't know enough about the mechanics of it to be sure, and why would he make up something like that anyway, especially in a class which was preparing me for an exam at the end of two years?
I understand your analogy with the train carriage Huw, and if I'm the person who's reducing the pressure at one end of the straw, then I'm doing the sucking, whether it's me or atmospheric pressure doing all the work. But all the same, it still feels like I'm pulling the liquid into my mouth. Thanks to both of you for trying to enlighten me - an almost impossible task