Random thoughts on infinity

[legmog]

Hey guys.

MASSIVE Science newb here. But recently I've REALLY started to get into it. Been watching lots of interviews / documentaries etc...

I would LOVE to get answers (or just enter into a dialogue) concerning my questions from people who know their stuff!

 

I've read that on account of the Big Bang,the universe is expanding, and that one day, galaxies and stars etc, will be SO far away, the night sky will be dark and no telescopes will be able to pick anything up insofar as light goes.

 

So I cooked up this theory in my mind.... IF the nature of infinity is more akin to a circle rather than a straight line (i.e... If I set off in a spaceship, and travel straight, I will one day arrive back where I started).... Then surely, one day... ALL the stars / galaxies that have gone so far away, will RE-APPEAR in the OPPOSITE direction? So if I look into a telescope and whitness a Galaxy moving away from us to the point where we no longer see it...... X ammount of time later, we surely should be able to turn that telescope in the absolute OPPOSITE direction and see that same Galaxy? Only now it's headed toward us as opposed to going away from us right?

 

 

Ergo...

- Big Bang happens

- All matter in the universe shoots away in all directions but ultimately comes BACK around to where it started (assuming heat death doesn't occur before this can happen)

- Big Crunch occurs

- All matter gets so dense in Big Crunch it EXPLODES back out into another Big Bang and Universe is renewed once more.

 

So my theory is.... Based on the above.... That the Universe is actually a big 'self perpetual motion' machine!

 

 

I would love to hear your thoughts on this

Tell me I'm wrong and why ^^.... I have a great thirst for scientific discovery right now!

[Phi for All]

So I cooked up this theory in my mind....

 

!

Moderator Note

Welcome to SFN! No offense, we keep the mainstream sections free of anything but mainstream science. We get a lot of students, you understand, who come here for help with schoolwork.

 

Soooo, I'm going to move this thread over to our Speculations section. Hypothesize all you like, try to back up any assertions with evidence, questions are always a good sign, and again, welcome.

[Mordred]

The big bang isn't an explosion. There is no single point of origin.

 

Read the articles here including the balloon analogy.

 

 

 

http://cosmology101.wikidot.com/redshift-and-expansion

http://cosmology101.wikidot.com/universe-geometry

 

Misconceptions (Useful articles to answer various Cosmology Misconceptions)

 

http://www.phinds.com/balloonanalogy/: A thorough write up on the balloon analogy used to describe expansion

http://tangentspace.info/docs/horizon.pdf:Inflation and the Cosmological Horizon by Brian Powell

http://arxiv.org/abs/1304.4446:"What we have leaned from Observational Cosmology." -A handy write up on observational cosmology in accordance with the LambdaCDM model.

http://arxiv.org/abs/astro-ph/0310808:"Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe" Lineweaver and Davies

Edited March 10, 2015 by Mordred

[legmog]

No problemo!

This 'speculation' forum seems like a pretty funky place

 

Thanks for the response also. Though I must admit, I did not read the entirety of all those links. A bit TOO intense for my mere mortal brain

Things like this video here are more up my alley

 

So errrmm.... Based on the above links, and kinda off this video. I have a few more questions.

 

1 - So we believe the Universe (and I guess by proxy, 'infinite' also) is FLAT rather than spherical / saddle shaped. So if I did fly off in a rocket in a straight line, I would NOT return to my original destination?

 

2 - Going on from the Baloon expansion idea... Am I to take it that (as the video puts it) Baryonic matter is NOT expanding. So all the Galaxies / stars etc are only PHYSICALLY moving away from one another almost as if they are being DRAGGED along by the Universe expansion? They themselves are not actually expanding?

 

Thanks!

[MigL]

The universe may have positive or negative curvature. It is not necessarily flat.

If it did have positive curvature, and was finite, then there could be a way to go off in one direction only to re-appear coming from the opposite direction. But just because a path exists doesn't mean it would be feasible.

The mistake you're making, is thinking the receding galaxies are actually 'moving' away from us; they are not.

Consider a circle with dots around the circumference. Obviously if you start at a specific point and go in one direction around the circumference you eventually return to the starting point from the opposite direction. But this is not the same as the galactic recession due to expansion. That can be visualized as the circle expanding, such that the arc between points on the circumference gets larger. The points are not actually moving around the circumference.

They will never reappear from the opposite direction.

And neither will receding galaxies.

[Mordred]

Also the flat/curved is a density profile its a comparison of the Universes actual density to its critical density. (Calculated density at which the universe will expand, slow down then start collapsing)

The first two articles I linked cover the above questions. Expansion only affects the regions not gravitationally bound. Galaxies are not dragged, the volume of space between large scale structures simply increases.

[Endercreeper01]

That is already a theory. It is called the big bounce: http://en.wikipedia.org/wiki/Big_Bounce

[Mr. Astrophysicist]

Hey! Welcome to the science forums, I hope you have a great time here. Going to the topic, the Big. Bang Theory is not an explosion. It is a common misconception, but its name implies it was an explosion, so don't worry. Besides that random idiot who named it the Big Bang theory, it should be called: the everywhere stretch theory. This theory explains that our universe at the beginning of time , at which it's space expanded from a singularity, as atoms, particles, and molecules settle, stars, comets, asteroids, galaxies, superclusters of galaxies, so on so forth form, they cooled down over a long period of time, and the dark energy process began (where space is expanding due to dark energy and galaxies start to away from each other at extraordinary rates). Once clearing that concept, let's get to your hypothesis. If you move from one position from another and continued walking, you would end up where you were, because earth is a shape close to that of a sphere, given any three dimensional shape, you can walk for several miles and end up in the sane spot because a circumference has to end. So here is one problem with your theory:

-The universe is hypothetically a sphere, maybe even flat. But given any of this shapes, this would not even work. If there was indeed a shape of the universe, we would not be at the edge of the universe, but rather somewhere within it's radius or generally its diameter.

-Dark energy sends the objects in space farther away from each other, but given the statement above, it would not be possible they would reappear in the opposite direction. If anything, they just spread continuously.

-Big crunch cannot be confirmed, and we would be long gone before then, neither can we significantly prove with just logic, because in the cosmos, phenomenal and such are bound to happen. That's why it's called a theory.

-That theory has been published or maybe not, but check out the holographic universe theory...

[Strange]

Besides that random idiot who named it the Big Bang theory

 

That "random idiot" was one of the most important astronomers of the 20th century. (Although he did have some odd views...)

[Mordred]

Ah universe geometry, so many misconceptions in regards to what is universe geometry.

 

In point it is a density relation between the universes actual density and the critical density.

It's not it's actual shape as per se. The relationship above determines whether the universe continously expands or contracts. This is regardless if it is finite or infinite.

 

If it's finite and contracts you can have the big bounce.

 

Keep in mind this is before dark energy was added.

 

Anyways that's the side note. Here is an article covering the actual vs critical density relations in terms of geometry. (I tried keeping it as simple as possible and still show the FLRW metric.

 

http://cosmology101.wikidot.com/universe-geometry

page 2 FLRW metric (distance on each geometry)

 

http://cosmology101.wikidot.com/geometry-flrw-metric/

[TheDivineFool]

Hi all.

 

I know that the 'expansion of the universe' is illustrated by an expanding balloon with dots painted on it representing galaxies. As the balloon expands, the distance between the dots increase. The point being 'distance between galaxies increase' BUT 'the galaxies are not moving'.

 

My limited knowledge tells me that A and B are in motion with respect to each other if the distance between them changes. This is clearly the case but physicists always maintain that the galaxies don't move. Something's wrong with my definition of 'motion'.

 

Could someone clarify how physicists define 'motion' so that I may understand how the galaxies are getting further and further apart but there is no motion.

 

Thanks.

Edited March 30, 2015 by TheDivineFool

[Strange]

It is an analogy, to try and make a distinction between relative motion and the increasing separation of objects due to expanding space.

 

The trouble is, it doesn't really make sense because motion can only be defined relative to something else. But one reason it is explained like this is because relative motion (according to the special theory of relativity, SR) says that the relative speed of an object must be less than c, the speed of light. But because recessional velocity is proportional to distance, there must be galaxies that are moving away from us faster than c. And there are (we can see some of them!) But that is allowed in general relativity (GR) because we are no longer dealing with inertial frames of reference.

 

I think it really comes down to whether the motion is "local" (can be treated as two inertial frames of reference and described by SR) or not (needs to be described by GR).

[Mordred]

Motion is also based on inertia, take a uniform pressure on every side of an object. As this pressure is uniform no inertia or acceleration can be imparted upon said object.

 

This is the case for large scale structures and galaxies due to expansion. Instead the volume of space between those structures is increasing. We know this by understanding the cosmological constant as a uniform vacuum or pressure. Therefore there is no pressure difference on one side to the other. It cannot gain momentum or inertia due to the cosmological constant.

[Strange]

The other distinction (implied by what Mordred said) is that if two galaxies were simply moving apart, then the speed of separation would be constant. However, when the space between them is expanding evenly, then the speed of separation must be proportional to distance (just simple geometry).

[TheDivineFool]

I feel like a broken record but if the galaxies are not moving what do you mean by 'speed' of separation?

 

Have scientists failed to define their terms accurately? Are they using these words 'motion', 'speed' loosely to make science understandable to the layman or is this real scientific language?

 

I though science was about crispy clear concepts. This confusing terminology is very unscientific to me.

 

Please clarify, if worthwhile. Thank you.

[Strange]

I feel like a broken record but if the galaxies are not moving what do you mean by 'speed' of separation?

 

Think of it as movement if you like. But read the previous points to understand why it can't be explained by, for example, giving all the galaxies a "push" to send them moving away from our galaxy.

 

Actually, that's another important point. If it were that sort of motion the, not only would their speed be constant, but it would place the Earth at the center of the universe. Which seems unlikely.

 

Are they using these words 'motion', 'speed' loosely to make science understandable to the layman or is this real scientific language?

 

The former. This is a problem of much of the popular explanations of science.

 

I though science was about crispy clear concepts. This confusing terminology is very unscientific to me.

 

The trouble is that an accurate explanation probably requires an understanding of the math of GR.

 

Edited March 30, 2015 by Strange

[Phi for All]

I though science was about crispy clear concepts.

 

It is, but it often requires you to know the concepts thoroughly before they gain their crispiness. It's a huge part of the problem that the average person thinks these crispy clear concepts should be obvious as well, even if you haven't studied them.