Universe's Expansion and Contraction

[Kenn]

Guys good morning. I have had this question  a long time now. We all know the Big Bang Theory right? So, here it is. The universe is expandin (either redshifting or blueshifting), however, if it is, then where is it expanding into? or where is it contracting from? is the universe endless? if not, where really is its end? or is it like a sphere wherein when you travel a straight path you will originally come into the point where you started? I'll be glad to have your answers. Thanks!

[impactcrater]

the greatest minds in Cosmology don't know the answer to that one .......Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. Albert Einstein

[kilix]

I suggest you watch PBS' Space Time videos, especially the series "Cosmology", "Origin of matter and time" and "Understanding dark energy" but you may not understand everything without studying further.

https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g/playlists

Universe does not need anything to expand into, that question is meaningless. Like asking "what was before the Big Bang", there was nothing before, how could there be any "before" when time did not exist? Universe is expanding, but what into? There is not any free endless space waiting to be filled with our Universe. Actually, there is no space outside of our Universe, one of building blocks of our Universe is space itself. I believe asking what is outside our Universe is an undefined question, you are asking about a place outside our Universe, that place cannot be defined outside of our Universe. Terms like "time" and "space" only make sense in our Universe.

It's like asking "how does a 30cm ruler continue after the 30cm mark?" It does not.

These topics are contradictory to our brains' perspective of everyday life and therefore terribly hard to grasp. I don't claim I understand In fact, the more I know, the more I study, the more confused I am.

This topic is not easily explained without prior knowledge. One of your questions can be answered safely thou - you cannot travel to the other side of the Universe, and the Universe appears flat, not curved as far as our knowledge goes, so it is not like a sphere. When you travel long enough, far enough, you will never reach the end of the observable universe, it would require infinite amount of time, because of expansion. If you really insist and continue to travel for tens of billions of years at almost lightspeed, you may find yourself surrounded by emptiness with no galaxies, no stars, no matter anywhere, not even ten billion light years away from you.

[ollypenrice]

The universe is not like anything else we think about or talk about. It's imoportant to remember this. TV programmes about the big bang often show a kind of explosion seen from the outside but this is totally misleading. There isn't an outside, just as kilix said. The universe is everything.

And it isn't an explosion. An explosion has a centre from which everything else is blown away. The universe doesn't have either an outside, an edge or a centre. And the expansion is not from one point. Every morsel of space (except where strong gravitional fields hold it back) is expanding.

Think of a balloon's surface as it is being inflated. (Do not think of the whole balloon, think only of the surface.) All of the surface is getting bigger throughout the inflation. There is no 'centre' on the surface. No one point is any different from any other point. But all points on the surface are moving away from each other as the surface grows. This is an example of expansion without a centre. (The balloon has a centre but its surface does not.)

[Vox45]

I was most disapointed when I learned that the "expansion" part was not what I had imagined

"Inflationary Epoch, from 10–36 seconds to 10–32 seconds: Triggered by the separation of the strong nuclear force, the universe undergoes an extremely rapid exponential expansion, known as cosmic inflation. The linear dimensions of the early universe increases during this period of a tiny fraction of a second by a factor of at least 1026 to around 10 centimetres (about the size of a grapefruit)"

[impactcrater]

this is always a good 'head' topic and therein lies the problem of what the human mind is capable of conceiving......whilst the concept of 'space' or the three dimensions is something we can touch there is no theory about what time is...perhaps time is infinite and space is finite...there may have been time before the Big Bang.....we have no way of knowing that is not true.....Einstein put space-time together but he could be wrong.....

[goodricke1]

As Neils Bohr said: 'We are suspended by language"... If there was no 'before' the BB then how can there be an 'after' the BB, since without a definition of 'before' the definition of 'after' loses its contextual meaning....

And the balloon analogy has always troubled me; any balloon I can imagine is surrounded by the wall of the house, or the sky, or whatever.... but the Universe is not 'surrounded' by anything.

[saac]

8 hours ago, goodricke1 said:

As Neils Bohr said: 'We are suspended by language"... If there was no 'before' the BB then how can there be an 'after' the BB, since without a definition of 'before' the definition of 'after' loses its contextual meaning....

And the balloon analogy has always troubled me; any balloon I can imagine is surrounded by the wall of the house, or the sky, or whatever.... but the Universe is not 'surrounded' by anything.

That shows the danger in reading too much into models like the balloon analogy, like all models it comes with limitations. The trouble is these models become popularised and too often little priority is given to describing the points at which the model breaks down. 

Jim

[ollypenrice]

On 17/03/2017 at 13:16, goodricke1 said:

As Neils Bohr said: 'We are suspended by language"... If there was no 'before' the BB then how can there be an 'after' the BB, since without a definition of 'before' the definition of 'after' loses its contextual meaning....

And the balloon analogy has always troubled me; any balloon I can imagine is surrounded by the wall of the house, or the sky, or whatever.... but the Universe is not 'surrounded' by anything.

Do we need 'before' to define 'after?' I don't see that we do. Time, as a dimension, might have come into being at the Big Bang creating, in that instant, 'now' and in subsequent instants 'after.' But it never created a 'before.' I don't see a big problem here, any more than with a question like 'where was the lottery winner before they drew the ticket?' It's a meaningless question because there was no lottery winner before they drew the ticket. The lottery winner came into being in that instant. Yes, there was a person before then but not a lottery winner. Maybe there were other dimensions before our time was born but, when we talk of our time, I don't see why it couldn't have had a beginning.

Not that I think we have a remotely complete theory of time. I'm sure wo don't.

There is no balloon analogy  as I really tried hard to emphasize. The analogy is with the surface of a balloon. In this analogy we remove all other dimensions, so the balloon has no three dimensional existence - we delete that in our minds - nor does it exist in any three dimensional space. That, too, is deleted. So the balloon is not a sphere and it is not in a room or any other kind of space. Its surface is space. Only its surface exists.

16 hours ago, saac said:

That shows the danger in reading too much into models like the balloon analogy, like all models it comes with limitations. The trouble is these models become popularised and too often little priority is given to describing the points at which the model breaks down. 

Jim

The limitations of the model are that we find it hard to use it correctly. We insist on thinking of the three dimensional existence of real balloons when, for the model to work, we must not do that. The only spacial dimension in the model is the surface of the balloon.

I like the surface of the balloon analogy. Let's say the balloon is pink. Therefore the only spacial dimension which exists is pink. If it isn't pink it doesn't exsit as a spacial dimension as you think about this.

[saac]

I tend to avoid its use in class, the students have a tendency to read too much into it; they end up stretching the analogy too far and this introduces persistent misconceptions.  For those who like the balloon analogy then this article is a useful starting point to identify its limits.

The Good Bad and Ugly Of The Balloon Analogy

Jim 

[SilverAstro]

30 minutes ago, saac said:

 stretching the analogy

I agree, I think the analogy has become inflated over time. The thing is, what happened before the baloon and its analogy came into existence ?

I think there must be a Dark Force perpetuating this analogy. Goodyear ?

coat >>

 

[saac]

1 minute ago, SilverAstro said:

I agree, I think the analogy has become inflated over time. The thing is, what happened before the baloon and its analogy came into existence ?

I think there must be a Dark Force perpetuating this analogy. Goodyear ?

coat >>

 

"Became inflated over time" 

 

Jim

[SilverAstro]

If the proverbial flatlanders lived on the 2D surface of our balloon what would they make of a small weight placed on the top of it ?

 

[saac]

My main objection is the questions it raises on the shape of universe - maybe I'm using the wrong balloons  

 

Jim

 

 

[SilverAstro]

Which would my flatlanders derive first,. Kepler's Laws or Minkowski geodesics ? and what would they make of that Great Attractor.

[ollypenrice]

Awe, you're being very unkind to the surface of the balloon analogy!

lly

[johnfosteruk]

1 hour ago, SilverAstro said:

I agree, I think the analogy has become inflated over time. The thing is, what happened before the baloon and its analogy came into existence ?

I think there must be a Dark Force perpetuating this analogy. Goodyear ?

coat >>

 

really? Allow me to get your coat... and don't come back

I've always thought the balloon analogy was perfect, if taken in context and not stretched. Also, none of the points raised in the 'good bad and ugly' article are going to be a problem if the context is properly set, and also also, is an analogy not a correspondence or partial similarity, a thing which is comparable to something else in significant respects? The partial and significant elements being key. 

When using an analogy one has to make it clear that this is what you're doing, set the context. I don't see a problem

[goodricke1]

7 hours ago, ollypenrice said:

There is no balloon analogy  as I really tried hard to emphasize. The analogy is with the surface of a balloon. In this analogy we remove all other dimensions, so the balloon has no three dimensional existence - we delete that in our minds - nor does it exist in any three dimensional space. That, too, is deleted. So the balloon is not a sphere and it is not in a room or any other kind of space. Its surface is space. Only its surface exists.

If we remove these vital characteristics of your common garden balloon, I think the analogy loses the essence of its meaning for the average layman. No, we need to stand up for balloon rights, puncture the overblown hype, and foster an understanding that all balloons are created equal

[SilverAstro]

1 hour ago, johnfosteruk said:

 and don't come back

Excellent ! That is another 'sphere' analogy that is no longer any good in the new cosmology, I wont be able to !  If, it was said, you head out in any direction and continue for long enough you will eventually arrive back at your origin, just like a traveler on earth, or a flatlander on a balloon. Or fire a very powerfull gun and if space were curved you'd shoot yourself in the back of the head.

Now, with space expanding at an ever faster rate I would eventually need to travel faster than c  to attempt to get back here

[johnfosteruk]

Where's the shaking head emoticon???

 

[SilverAstro]

34 minutes ago, SilverAstro said:

Now, with space expanding at an ever faster rate I would eventually need to travel faster than c  to attempt to get back here

Actually, I think that was true even before Perlmutter et.al  with just the 'ordinary' (!) expansion.

[Alien 13]

I dont like the balloon, although space and time came into existence shortly after the big bang the whole universe might still be smaller than an atom.

Alan

[SilverAstro]

20 hours ago, goodricke1 said:

 puncture the overblown hype,

but common balloons ? oh dear me no, tsk tsk, this is SGL d'y'kno, nothing common here

No, some of my balloons are coloured (QBD)  (Quantum ChromoDynamics) and some are Up (Hydrogen filled) and some are Down (CO2) and yet others have Charm ( see @saac earlier), in fact if you rub them with a finger they can even sound like " quurkkk"

So you see, with the analogy to expanding space-time and with mass on a rubber sheet plus QBD etc. I am well on the way to establishing a quantumGravity GUT of Everything, (Grand Unified Theory)

[impactcrater]

there's always the raisins in th cooking cake analogy and when the Universe finishes expanding you can always eat it ! it seems much more appetising than the balloon analogy....