expanding universe

[j_rankin]

I can't see what the big question is.

If you drew a circle, and then drew a line coming out of the centre of the circle at 1 degree at the same time as you drew a line coming out at 2 degrees, then both lines would keep getting further and further apart, quicker and quicker.

If the universe started with the big bang, and the re-ionisation period took place, then galaxies would have all head out at a particular angle (unique for every galaxy), meaning that they would have all kept getting further and further away from each other, quicker and quicker. Gravitic affects would have then come into play and kept galaxies in relative clusters as they moved out through space.

Please explain why this is wrong cos i can't figure it out.

[ramparts]

Unless I'm misunderstanding you, that sounds more or less right. As the universe gets larger, objects in different locations (corresponding to objects along different points on expanding circles, in your picture) get further apart. Perhaps I'm misunderstanding you. Is there something that made you think this was wrong?

The one thing I will note is that in your circle analogy, there's a center. As you've likely heard before, there really was no center to the big bang, so that might not be the best analogy for that reason. (A better analogy here would be the expanding balloon, where everything on the surface of a balloon moves further from each other as you blow it up, but there's no center to the balloon's surface.)

[j_rankin]

what im not understanding is why it's such a surprising thing that the universe seems to be expanding at an accelerated pace.

Correct me if im wrong (which i probably am), but as far as im aware the only evidence we have that the universe is accelerating is because the distance between galaxies is getting greater faster and faster.
But my analogy, which assumes that the universe expanded from a single point, explains why.

If you took 2 cars and set one off driving at 1 degree north and another car at 2 degrees north, both travelling at the same speed, then the distance between the 2 cars would keep getting greater and greater at a faster and faster rate.

If the big bang occurred, then how could it not have a point of origin?

[MeteorWayne]

First, you are confusing two different things. One is the expansion, the other is the acceleration of the expansion recently (over the last 5 billion years or so). It's confusing velocity with acceleration; they are two different things. For example if you are in your car going 60 miles an hour on a straight road, your veleocity is 60 mph, but your acceleration is zero. If you then speed up to 75 mph, your new velocity is 75 mph (watch out for the cops! ), and you accelerated from 60 to 75 mph in that time interval.

The expansion was driven by the big bang itself. There's no doubt about that.

The more subtle thing is an acceleration in the expansion recently; that cause (whatever it is) is what is called "dark energy". The case is not 100% firm that this is actually occurring, but as more and more data is collected the case becomes stronger.

And as far as why there is not a point of origin, it's because all of space is expanding, not from specific point, but from every point.

[SpeedFreek]

The more distant the galaxy we observe, the faster it recedes from us. But the evidence that the expansion of the universe is accelerating is not due to the fact that the further we look, the faster the objects are moving away, which would be the case with any kind of expansion (decelerating, constant or accelerating).

Imagine a rubber band, with equal distances marked off on it at intervals of 1cm. When we stretch the rubber band, all the distance markers separate from their neighbouring markers at the same rate. All distances across that rubber band increase by the same factor, all the markers separate equally as it stretches.

Hold an end in each hand and stretch the band until all the markers are twice as far apart as they were to begin with. Now look at the viewpoint from one of your hands. The marker right next to your hand is now twice the distance away that it was before you started stretching it. But if you look at the tenth marker along, you will find it is now twice the distance away it was to begin with too.

Let's say you took 1 second to stretch the band to twice its original size, making all the markers twice the distance apart that they were to begin with.

The 1cm mark is now 2cm away, and the 10cm mark is now 20cm away. The 10cm mark has travelled 10 times the distance from your hand that the 1cm mark did, in the same amount of time. The first mark moved at 1cm per second, whilst the 10th mark moved at 10cms per second.

The further away a marker was from your hand, the faster it moved away from that hand, and this is what we mean when we say the further away an object is, the faster it recedes.

At any given time across that rubber band, distances are increasing at the same rate as each other, so all markers separate equally.

It doesn't matter if you start stretching the band fast and then slow it down, or start stretching it slow and go faster and faster - the furthest point you measure will always be receding the fastest.

So, the observation that, the further away a galaxy is, the faster it is apparently receding, is not what tells us that the rate of expansion is accelerating. All it tells us is that the universe is expanding metrically, like the rubber band.

What tells us that the rate of expansion is accelerating are observations of a certain type of supernova (known as "standard candles" because of their predictable properties), across a range of distances. We know that the rate of expansion was decelerating for billions of years and had expected this to still be the case, but we found that the closer the supernovae we looked at, the dimmer they were than is to be expected in a decelerating universe. The closer we looked, the further away those supernovae were from the predicted distance. As we look at them at increasing distances, the closer they get to the predicted value for deceleration.

The conclusion is that, around 5 billion years ago, the rate of expansion ceased in its deceleration and started to accelerate.

The rubber band was stretching incredibly fast to begin with but immediately slowed and continued slowing for around 8 or 9 billion years. Then it gradually started to get faster again. So, when we look at the closest markers, they are further apart than they would have been if the stretching of the band had continued to slow.

[R1]

It's a little confusing sometimes, I just came from a different thread and I was posting about the
universe not having a single point origin (as in a center).
(There are also threads about gravity speed both here and downstairs in the unexlained.)
Anyway, I really like your explanation Speedfreek.

I remember two or three years ago hearing people explain to me that because the more distant
objects are receding faster than expected, that I was supposed to understand when they told me that
the universe expansion is accelerating.

I'm glad that got straightened out (I think it did), because I kept insisting that information about
the furthest objects is actually about how things were 'before', not 'after'.
----------------------------------

Would the deceleration have anything to do with the fact that the entire universe suddenly (but after inflation)
had all the mass of the universe ?


(I asked somewhere else also if there is any way possible that inflation and dark energy are related?)

[SpeedFreek]

I hope my explanation did not imply a centre to the universe, as it doesn't matter which mark you choose as your viewpoint on the rubber band, the further away one mark is from another, the faster that mark moves relative to the other (and of course, the further away an object is, the longer it takes information about it to reach you).

You might find these posts interesting.

Would the deceleration have anything to do with the fact that the entire universe suddenly (but after inflation) had all the mass of the universe ?

(I asked somewhere else also if there is any way possible that inflation and dark energy are related?)

The deceleration was due to gravity, so you could say it was the mass of the universe. Indeed, before we discovered that the rate of expansion was accelerating, a big question in cosmology was whether there was enough mass in the universe to bring the rate of expansion to a halt or not. With enough mass, the expansion of the universe would slow down to a halt and then the universe would start to contract again. With not enough mass, the universe would expand forever. What was not expected was that the expansion, rather than slowing down towards a halt but never reaching it, or slowing down to a halt and then contracting, had slowed down for a long time and then started to accelerate instead.

So, with the acceleration of the expansion there has to be more at work than simply the initial expansion from the Big Bang, and gravity having an effect on that expansion.

As to your other question, it is possible that inflation and dark energy are related. In one possible scenario, dark energy might be a remnant left over from inflation. If the "inflaton" field, which seemingly acted something like repulsive gravity, did not quite disappear at the end of inflation (i.e. it remained at a very low, but non-zero value), it would only manifest itself again once everything at the large scales was far enough from everything else for it to have a measurable effect.

[R1]

That is what I think.


-------------------------------------------------------------------------------------
Ok, here is the sequence of the following events as I understand them so far:



In the beginning, there was no mass at all, and no gravity. Nothing.

Then dark energy may have been responsible for inflating energy.

The universe was still massless. No thing of mass existed.
Then, after inflation, the energy (scattered by what could be dark energy), played
a major part in creating all the mass and potential mass of the universe.

Now, the young and small universe soon had all the mass and potential mass of the
universe, and its expansion began to slow as a result of 'all' this mass (which did not exist until now).

Later, however, in the past 5 billion years, the expansion has been accelerating and
possibly due to the dark energy.

[johnlesse]

If the universe expanding why we are not collide with other universe or other elements on space?

chiropractor marketing

[R1]

If the universe expanding why we are not collide with other universe or other elements on space?

I think another universe would only be part of this one.
I also don't think that the universe is discontiguous.


edit /add -- But I add a somewhat parellel question:
If the universe is closed like a balloon, and it expands extremely fast (FTL), could dark energy
expansion be due to an 'overlap' of undisturbed spacetime expansion?

In other words...some kind of expansion collision with itself?

[michaelmozina]

You might find these posts interesting.

FYI, Michal Chodorowski has another impressive paper out that you might find interesting.

http://arxiv.org/abs/0911.3536

[janewhite]

Our universe has been expanding gradually . The Big Bang theory does supports to this. The Big Bang is the cosmological model of the initial conditions and subsequent development of the Universe that is supported by the most comprehensive and accurate explanations from current scientific evidence and observation. As used by cosmologists, the term Big Bang generally refers to the idea that the Universe has expanded from a primordial hot and dense initial condition at some finite time in the past (currently estimated to have been approximately 13.7 billion years ago), and continues to expand to this day.

[ZenGalacticore]

Hello Jane. Welcome.

The "Universe has been expanding gradually."

"Gradually" relative to what?

[acsinnz]

and continues to expand to this day.[/quote]
Yes, Jane. It is still expanding because probably there is an electrical repulsive force not only between stars but also between the induced super negative black holes at the centre of each galaxy. This electrical force is just stronger than the mass attraction of matter to matter. Dark energy is almost certain to be electrical. Clive

[origin]

Yes, Jane. It is still expanding because probably there is an electrical repulsive force not only between stars but also between the induced super negative black holes at the centre of each galaxy. This electrical force is just stronger than the mass attraction of matter to matter. Dark energy is almost certain to be electrical. Clive

Probably? Almost certainly? And this is based on what your wishes or hopes. An electrical repusion between the stars that overcomes gravity would certainly be readily detectable. How does your theory explain multiple star systems? Why are the milky way and the andromeda galaxies heading towards each other if there is such a huge negative repulsion between them.

Your theory does not hold water, or a charge for that matter.