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the expansion theory


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i joined up to this site a while back after starting to find myself more interested in astronomy, the universe and physics

instead of rushing out and buying anything i thought i'd learn a little first, it's mind blowing at how many questions can be raised in a few short minutes.

here are some of them.

if the expansion theory is right and the univrse is expanding ever outwards to the point where billions upon billions of years from now the milky way will find its self alone with no light visible from distant galaxies and the more outwards you expand the faster it gets then how is it possible for galaxies to collide and merge.

now i'm new to the world of physics so to some it may seem a stupid question but:

1 the big bang set everything in motion so as an explosion has a start and an end there is only so much energy that can be set free at a single point in time, this would suggest that everything moving outwards would be moving at the same speed with the same amount of energy pushing it outwards.

2 in zero gee space unless a galaxy can produce its own thrust how is it possible for things to speed up the further out you get.

3 if everything is moving outwards from everything else no matter where you happen to be in the universe how is it possible for galaxies to collide

4 the fact that galaxies do collide and merge would suggest that motion and direction are random which would defunk the expansion theory.

you may all now laugh and leave sarcastic comments :):icon_scratch:

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The big bang was not an explosion of matter into space, rather it was an explosion of space itself, and since space and time are interconnected, we really have to say it was an explosion of space and time, or space-time.

So, the big bang wasn’t an explosion of stuff like atoms or molecules, it was an explosion of a place and instance, it was the creation of when and where.

Alot of people think of the Big bang as an explosion. It was not, I like to think of it as the big Expansion...

Almost instantly the universe gets very large, driven on by the vacuum of space it expands, and space and time are created.

So as there is no centre and the expansion is from all direction we have blue and red shifts hence why galaxies do collide from time to time.

Think of the ant on the balloon theory as this describes it very well.

Edited by Doc
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the big bang was indeed the explosion of space and time as well as matter.

the big bang theory states that all the matter in the universe was compressed to a single point no bigger than a sub atomic particle then bang everything we know came into existance.

and as all matter is energy and all energy is matter the big bang was an explosion.

an explosion being a sudden release of energy.

am i wrong ?

i was hunting for info on the red and blue shifts can you point me in the right direction

cheers

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Forget explosions. Space is expanding. Explosions describe things moving through space, which is not the same at all. The expansion of space is not all that fast over local scales so gravity (holding nearby things together) easily overcomes it. Our own galaxy is not expanding because it is gravitationally bound; its mutual gravity overcomes the expansion of space. Indeed local galaxies also overcome the expansion of space through their mutual graviational attraction. We and M31 are falling towards each other, as are many neighbour galaxies. (In your 'point 2' you are clearly thinking of the distant galaxy moving through space. It doesn't, to any great extent. In its own bit of space it is just sitting there. However, the space between it and you is growing so it gets further away without, in the conventional sense, 'moving' at all.

When there is a lot of space between you and something else (a lot on an astronomical scale, that is) then there is a lot of expansion in that space, too much to be overcome by mutual gravitation (which weakens as the square of the distance) while the expansion gains over distance because there is more space to expand.

It's all good stuff!

Olly

Edited by ollypenrice
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I really think the term 'Big Bang' should be outlawed. as should the term 'God Particle'. They're terrible descriptions of what's going on, and lead to many misinterpretations and flawed conceptions.

"how can nothing explode?"

"scientists are trying to find a particle to prove God exists..."

'sigh' easily avoidable. people are just suckers for dramatic names, i guess, lol.

I think someone else may already have mentioned this, but let me expand (pun not intended):

Imagine an ant on the surface of a balloon that's being inflated. he has two friends, one initially sitting 1 cm away, the other at 10 cm. The balloon stretches evenly, lets say it has doubled in size after 1 second. thus, the ant sitting 1 cm away is now 2 cm away, and the ant sitting 10 cm away is now 20 cm away.

as far as our reference ant is concerned, ant one just moved away from him at 1 cm per second, and ant 2 moved away from him at 10 cm per second. but of course, as far as each ant is concerned, he's sitting still, everyone else is moving.

if we wait another second, the balloon doubles in size again, ant 1 is at 4cm, apparently now moving 2 cm per second, ant 2 is at 40cm away, apparently moving 20 cm per second, they appear to have accelerated.

if we now say that ants can run at 5 cm per second, if sufficiently motivated, and they all start running towards each other out of terror as the balloon begins to inflate, you can see how at short range, they can overcome the expansion and 'collide'. however, the poor fellow at 10cm will never be able to reach anyone, he soon shoots off into the distance.

Now, red and blue shifts. I'm sure you're familiar with the doppler effect: the change in pitch as an ambulance whizzes past, for example. you will often be told that this is what causes galaxies to appear redshifted. this is incorrect. well, mostly. doppler shifts are to do with relative motion, and as far as the observers are concerned, for the most part, they are stationary.

imagine on our expanding balloon, we were to draw a wave pattern between our two ants, a set number of peaks and troughs that remains constant. as the balloon expands, what changes is the distance between the peaks and troughs, the wavelength, nothing else.

now, all light can be understood as waves, shorter wavelengths we perceive as blue, longer wavelengths we see as red. as the balloon, or universe, expands, the wavelengths of the light travelling between the galaxies increases, because the space it is covering is expanding, but the number of peaks and troughs remain constant.

The more distant something is, the longer it takes to get to you, so the more time space has to expand. thus, the farther away something is, the redder it appears.

now, the doppler effect does also come into play, since galaxies may be moving relative to each other rather than sitting stationary in the expanding universe, but for the most part, this effect is much smaller than that of space expanding, such that it is only really important in relatively close galaxies .

it is most noticeable when said nearby galaxy happens to be moving towards us rather fast, so that the doppler blue shift of it moving towards us cancels out the redshift from the expanding space. this is how we know that the andromeda galaxy will collide with our own in a few billion years, should be quite a sight!

i realise i may have waffled a bit here, and probably haven't actually answered your questions, but i'd be happy to clarify anything. :rolleyes:

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Very good analogy from tom142.

The term Big Bang was coined by Fred Hoyle, who was not a believer. It was meant to be derogatory. His own cosmological model, the Steady State theory, did have the universe expanding but only slowly. The discovery of the microwave background (predicted earlier as a consequence of the Big Bang) did for the Steady State, pretty well.

You may already know this but the evidence for the expansion comes from observations started by Vesto Melvyn Slipher and then extended vastly by Edwin Hubble with Milton Humason. The latter found that the redhift of galaxies increased with distance and there were two key additional observations. 1) This was true in whichever direction you chose to look. 2) The relationship between distance and redshift was linear. Double the distance, double the redshift.

So... to discount the Big Bang you have to believe that we are in the centre of this explosion or expansion (but why should we be?) and that if it is an explosion, in which galaxies are moving away through space, it is a strange kind of explosion in which there is no loss of energy over immense periods of time. You would have expected to see the most distant galaxies slowing down a bit, I think? (I'm not sure about that and would be interested to hear an expert opinion.)

Since the expansion of space removes the need for us to be at the centre and explains the linear relationship between redhift and distance, cosmologists like it. They like it even more since it meshes perfectly with General Relativity, a description of time, space and gravity which is, outside the atomic scale, apparently indestructible. Experimenters have been trying for nearly a century.

Olly

Edited by ollypenrice
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The only apparent alternative to expansion theory, is to say that the redshift is caused by every galaxy flying away from us at absurd speeds.

The problem is, it turns out that the expansion of space is not linear or even slowing down, as one might expect (it was thought for a long time that the gravity of objects in the universe should be slowing the expansion down), it's actually accelerating. This was observed by comparing the redshift with more conventional means of measuring distance.

This means, helpfully, that the Hubble constant describing the expansion is not a constant, and varies with time.

This is a big problem in cosmology, and has required the introduction of a repulsive 'dark energy' which would have to make up 74% of the universes mass/energy density and have negative pressure to account for the observations.

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ha ha, don't forget Big Rip, my personal favourite potential death of the universe, lol

In this scenario, the scale of the universe becomes unbounded (infinite) at some finite time in the future.

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  • 2 weeks later...

I love these conversations :D

thanks for the red,blue shift explanation i get it now i think ?

great stuff to be honest i wish humans could live for a couple of hundred years, can you imagine at some point in the not to distant future when new theories will smash what we know today.

to be around when that one eureka moment comes.

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But will it come? Einstein didn't smash Newton. How many scientific theories have been smashed since the 17th century? There is more refinement than smashing, I would say. However, there will, of course, be a breakthrough in thinking. I put my money on a new theory of time.

Olly

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But will it come? Einstein didn't smash Newton. How many scientific theories have been smashed since the 17th century? There is more refinement than smashing, I would say. However, there will, of course, be a breakthrough in thinking. I put my money on a new theory of time.

Olly

Luminiferous ether and steady state universe are the only major ones I can think of off the top of my head. You're right, the majority of theories are extensions and refinements of what's already known rather than complete replacements.

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What about the Electric Universe theory? Not read much myself, just seen a few videos showing how it can be used to apparently explain the formation of galaxies without the need for Dark matter or Dark energy.

I won't lie, this stuff just baffles me.

Reading your explanation on gravity overcoming space expansion I can't quite get my head around. You said our own galaxy isn't expanding because it's gravitational force has overcome the expansion of space, will it then not eventually collapse in on itself? I think I remember reading a theory along the lines of the center of our galaxy sends out a 'pulse' every so often which keeps the structure balanced.

I realise in this day and age we're advancing at an observable exponentiation rate, but would it be fair to assume that it's no longer for unlocking the secrets of the Universe, but instead power and greed. Thus alot of potential technological breakthroughs and theories are either forgotten about or kept from the public knowledge. Nikola Tesla, some of his experiments and theories seem just mind-blowing, yet I don't think he was ever mentioned in my A-Level Physics class, not sure about University.

From what little I've read, it seems to me that when something which cannot be explained within the bounds of the accepted model of the Universe is discovered, then it's twisted until it can be. But is it not the basis of Science to question what itself claims is fact? If not then surely it becomes a branch of 'religion'

Apologies If I've derailed the thread too much!

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What about the Electric Universe theory? Not read much myself, just seen a few videos showing how it can be used to apparently explain the formation of galaxies without the need for Dark matter or Dark energy.

I've not seen much on electric universe theory, but what i have appears to hold very little water. If you'd like any particular points discussed / contended, perhaps we could start a separate thread?

Reading your explanation on gravity overcoming space expansion I can't quite get my head around. You said our own galaxy isn't expanding because it's gravitational force has overcome the expansion of space, will it then not eventually collapse in on itself? I think I remember reading a theory along the lines of the center of our galaxy sends out a 'pulse' every so often which keeps the structure balanced.

Our galaxy doesn't collapse in on itself for the same reason our solar system doesn't - all the components are orbiting the centre of mass.

From what little I've read, it seems to me that when something which cannot be explained within the bounds of the accepted model of the Universe is discovered, then it's twisted until it can be. But is it not the basis of Science to question what itself claims is fact? If not then surely it becomes a branch of 'religion'

I would disagree. From my experience, problems are acknowledged when they are found, and hypothesis are suggested and predictions are made until sufficient evidence is present. There are a lot of hypothesis that people tend to assume scientists view as gospel, i don't think this is the case.

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' There are a lot of hypothesis that people tend to assume scientists view as gospel, i don't think this is the case. '

Exactly! The media tend to present scientists as declaring thngs to be 'so' when the scientists themselves take the view that they have a working hypothesis. We need better journalists.

I almost mentioned the luminiferous ether in my previous response but decided not to do so because I don't know all that much about its history. However, what is interessting is that an experiment was set up by Mickelson and Morely to demonstrate its existence, it failed, and out went the ether. What more can you ask of science? It was never gospel and had a very short life as an hypothesis, I believe.

Olly

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  • 1 month later...

1 the big bang set everything in motion so as an explosion has a start and an end there is only so much energy that can be set free at a single point in time, this would suggest that everything moving outwards would be moving at the same speed with the same amount of energy pushing it outwards.

No. No explosion, nor expansion, is completely uniform. The most minute variations at the beginning expand and destroy uniformity. The Cosmic Microwave Background Survey shows a general uniformity but when looked at locally it has a clumpy appearance. The recent discovery of "Dark Flow", one of which runs at near right angles to the surrounding expansion, to my mind suggests that though there was an expansion that accounts for the motion of most of the visible matter in our universe it probably expanded into something that was already there. Either that or there was not one point of expansion but many.

Others have done a great job of explaining expansion using the balloon analogy. But if you think about it if 'nothing' expands by 100% it is still nothing. So... so called empty space cannot be empty for expansion theory to have any credibility. An expanding ballon only expands because it has matter pumped into it. One candidate for this is the energy potential of the Zero Point Field (ZPF), which I think of as one of the hidden dimensions of space/time that exists on a quantum level. To understand this you would have to familiarise yourself with the theory of Quantum Chromodynamics which demonstrates that vacuum is not a vacuum but subject to the spontaneous appearance and disappearance of electrons in a given space. With probability vectors summed in this means there is no point in space that is really empty. From what I personally deduce from my reading on the nature of the ZPF is that it has the property of realised potentials stimulating exponentially more potentials and thus we observe an expanding universe. For example a single idea can lead to millions of further ideas. You can liken the brief excursion of an electron out of its potential and into existence as an idea that stimulates many more. I may be totally wrong, I probably am, but this is how I work it out in my head.

2 in zero gee space unless a galaxy can produce its own thrust how is it possible for things to speed up the further out you get.

I will leave this to previous explanations except to say that I think these explanations are flawed and such observations are an illusion.
3 if everything is moving outwards from everything else no matter where you happen to be in the universe how is it possible for galaxies to collide
4 the fact that galaxies do collide and merge would suggest that motion and direction are random which would defunk the expansion theory.
Galaxies do not exist as isolated islands but belong to galactic clusters within which they are gravitationally tied. So within the clusters there can be movement along any vector that can and do make galaxy collisions common.

Hope this has helped a little.

And..
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  • 3 weeks later...
  • 5 weeks later...
I really think the term 'Big Bang' should be outlawed. as should the term 'God Particle'. They're terrible descriptions of what's going on, and lead to many misinterpretations and flawed conceptions.

"how can nothing explode?"

"scientists are trying to find a particle to prove God exists..."

'sigh' easily avoidable. people are just suckers for dramatic names, i guess, lol.

I think someone else may already have mentioned this, but let me expand (pun not intended):

Imagine an ant on the surface of a balloon that's being inflated. he has two friends, one initially sitting 1 cm away, the other at 10 cm. The balloon stretches evenly, lets say it has doubled in size after 1 second. thus, the ant sitting 1 cm away is now 2 cm away, and the ant sitting 10 cm away is now 20 cm away.

as far as our reference ant is concerned, ant one just moved away from him at 1 cm per second, and ant 2 moved away from him at 10 cm per second. but of course, as far as each ant is concerned, he's sitting still, everyone else is moving.

if we wait another second, the balloon doubles in size again, ant 1 is at 4cm, apparently now moving 2 cm per second, ant 2 is at 40cm away, apparently moving 20 cm per second, they appear to have accelerated.

if we now say that ants can run at 5 cm per second, if sufficiently motivated, and they all start running towards each other out of terror as the balloon begins to inflate, you can see how at short range, they can overcome the expansion and 'collide'. however, the poor fellow at 10cm will never be able to reach anyone, he soon shoots off into the distance.

Now, red and blue shifts. I'm sure you're familiar with the doppler effect: the change in pitch as an ambulance whizzes past, for example. you will often be told that this is what causes galaxies to appear redshifted. this is incorrect. well, mostly. doppler shifts are to do with relative motion, and as far as the observers are concerned, for the most part, they are stationary.

imagine on our expanding balloon, we were to draw a wave pattern between our two ants, a set number of peaks and troughs that remains constant. as the balloon expands, what changes is the distance between the peaks and troughs, the wavelength, nothing else.

now, all light can be understood as waves, shorter wavelengths we perceive as blue, longer wavelengths we see as red. as the balloon, or universe, expands, the wavelengths of the light travelling between the galaxies increases, because the space it is covering is expanding, but the number of peaks and troughs remain constant.

The more distant something is, the longer it takes to get to you, so the more time space has to expand. thus, the farther away something is, the redder it appears.

now, the doppler effect does also come into play, since galaxies may be moving relative to each other rather than sitting stationary in the expanding universe, but for the most part, this effect is much smaller than that of space expanding, such that it is only really important in relatively close galaxies .

it is most noticeable when said nearby galaxy happens to be moving towards us rather fast, so that the doppler blue shift of it moving towards us cancels out the redshift from the expanding space. this is how we know that the andromeda galaxy will collide with our own in a few billion years, should be quite a sight!

i realise i may have waffled a bit here, and probably haven't actually answered your questions, but i'd be happy to clarify anything. :icon_salut:

never really understood the balloon analogy until i read your explanation many thanks

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