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Author Topic:   Size of the universe
Iblis
Member (Idle past 1972 days)
Posts: 663
Joined: 11-17-2005


(1)
Message 76 of 248 (598670)
01-01-2011 6:37 PM
Reply to: Message 75 by Philip Johnson
01-01-2011 6:26 PM


Re: Young or old universe
Are you of the opinion that nothing can go faster than the speed of light? Is the radius of the universe increasing by at most 1 light year every year since nothing can go faster than the speed of light?

This is a fairly common misperception. The expansion of space, both the current version including "dark energy" and the inflation version, is not limited by C because it is a change in the nature of spacetime and not a movement of objects inside spacetime. The most distant objects are not receding faster than the speed of light because they are in motion, but rather because the space between us and them is increasing relatively uniformly.

You may imagine a rubber band if you like. When we stretch it to twice its size, marks on it which were two inches apart are now 4 inches apart. But marks which were a foot apart are now two feet apart. Thus the further away an object is, the faster it is receding. But its not moving relative to spacetime at all. So C doesn't apply.

One easy way to think of it is to understand that space literally is nothing. And thus we see that nothing can move faster than light!


This message is a reply to:
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Replies to this message:
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Percy
Member
Posts: 18309
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 77 of 248 (598774)
01-02-2011 7:35 AM
Reply to: Message 75 by Philip Johnson
01-01-2011 6:26 PM


Re: Young or old universe
Philip Johnson writes:

Is the radius of the universe increasing by at most 1 light year every year since nothing can go faster than the speed of light?

Your mention of radius implies that the universe has a finite size, but we don't know that. It might be finite, it might be infinite, we don't have conclusive evidence either way at this time.

Iblis already provided the correct answer that space/time, being neither matter or energy, is not constrained by the speed of light (c).

If you're wondering what evidence tells us that matter and energy cannot exceed c while the expansion of space can, we can get into that if you like.

--Percy


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Replies to this message:
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jar
Member
Posts: 30934
From: Texas!!
Joined: 04-20-2004


(1)
Message 78 of 248 (598785)
01-02-2011 12:55 PM
Reply to: Message 77 by Percy
01-02-2011 7:35 AM


The lad, the light and the room.
Once there was a little boy who lived in a really big room. He was a very smart little boy and had a very bright little flashlight. When he stood real tall and reached up real high and aimed his little flashlight straight down, he could see the great circle of his universe laid out on the floor. But when he pointed his little flashlight away from the floor he could see nothing.

Daily he grew, and as he grew, and as he held his little flashlight higher and higher the great circle of his universe got bigger and bigger. But when he pointed his little flashlight away from him he could see nothing.

Soon he was all grown up and could reach really really high and the light from his little flashlight showed a much bigger circle of his universe laid out on the floor. But still, when he pointed his little flashlight away from him he could see nothing.

How big was the room?


Anyone so limited that they can only spell a word one way is severely handicapped!
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ProtoTypical
Member
Posts: 1775
From: Ontario Canada
Joined: 08-04-2010


Message 79 of 248 (599082)
01-04-2011 8:55 PM
Reply to: Message 77 by Percy
01-02-2011 7:35 AM


Re: Young or old universe
Iblis already provided the correct answer that space/time, being neither matter or energy, is not constrained by the speed of light (c).

I don't mean this to be a flippant question. How can something that is neither matter nor energy have any effect on matter or energy?


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cavediver
Member (Idle past 1720 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 80 of 248 (599129)
01-05-2011 5:29 AM
Reply to: Message 79 by ProtoTypical
01-04-2011 8:55 PM


Re: Young or old universe
How can something that is neither matter nor energy have any effect on matter or energy?

To make sense of this as a question, you need to understand better what you mean by matter, energy, and effect. And at that point, the answer would be obvious

I'll try to find time later to flesh out a more appropriate, less flippant response...

Edited by cavediver, : No reason given.


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Percy
Member
Posts: 18309
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


(1)
Message 81 of 248 (599136)
01-05-2011 8:00 AM
Reply to: Message 79 by ProtoTypical
01-04-2011 8:55 PM


Re: Young or old universe
Dogmafood writes:

I don't mean this to be a flippant question. How can something that is neither matter nor energy have any effect on matter or energy?

Cavediver will probably provide a better answer, but you're asking about the nature of space/time. Matter and energy exist within space/time, which means every photon and particle has a 4-dimensional position within space/time (3 spacial dimensions and 1 time dimension) and a 4-dimensional velocity vector. Both the position and the velocity vector will have values that are relative to the observer (that's why they call it relativity).

It turns out that space/time is not fixed, that space is expanding over time at a rate known as the Hubble constant, which is approximately 74 km/sec/Mpc (Mpc is a mega-parsec, a million parsecs, or about 3.2 million light years). Space itself (along with the matter and energy contained within it) that is a mega-parsec away is receding away from us at a rate of 74 km/sec. Space that is 2 mega-parsecs away is receding away from us at twice that rate, 148 km/sec. This recession velocity is due to the creation of new space in the intervening space.

Objects bound together with sufficient force (usually by gravity) are not affected by the expansion and remain together, but objects at great distances from one another exert very little gravity on each other, and the expansion of space is sufficient to carry the objects away from one another. Light is also affected by the expansion of space - it becomes drawn out and lengthened into longer (redder) wave lengths, we observe it as the red shift.

--Percy


This message is a reply to:
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Replies to this message:
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ProtoTypical
Member
Posts: 1775
From: Ontario Canada
Joined: 08-04-2010


Message 82 of 248 (599228)
01-05-2011 8:43 PM
Reply to: Message 81 by Percy
01-05-2011 8:00 AM


Re: Young or old universe
Matter and energy exist within space/time, which means every photon and particle has a 4-dimensional position within space/time (3 spacial dimensions and 1 time dimension) and a 4-dimensional velocity vector. Both the position and the velocity vector will have values that are relative to the observer (that's why they call it relativity).

No problem.

It turns out that space/time is not fixed,...

Whoa up there just for a moment. Space/time is neither matter nor energy, as per your words and my own understanding of it. It is not a thing until it is defined by other things that really are things like moons and molecules. I have always considered space to be a sort of ‘not a thing’. Fixed or moving or expanding are qualities that belong to things that are subject to relativity. Are they not?

This recession velocity is due to the creation of new space in the intervening space.

I understand that this is indicated by the model. I am stumbling because it requires me to consider space as a thing. Does space have a dual nature similar to light? Or is it just a failure of language? Is ‘the fabric of space/time’ more than just a figure of speech?

Light is also affected by the expansion of space - it becomes drawn out and lengthened into longer (redder) wave lengths, we observe it as the red shift.

Why does the red shift that we observe require the expansion of space? Is it because a galaxy that is 13.7 billion light yrs away appears to be receding at a rate greater than c?

Cavediver has warned me off of considering the BB to be like an explosion but I am finding that difficult to do. Is the nature of the universe, on a universal scale, fundamentally different from what I see around me?

These would be my definitions taken from http://www.thefreedictionary.com and edited ;

Matter - a. Something that occupies space and can be perceived by one or more senses; a physical body, a physical substance, or the universe as a whole.
b. Physics Something that has mass and exists as a solid, liquid, gas, or plasma.

Energy - 1. The capacity for work or vigorous activity; vigor; power.
a. Usable heat or power:
4. Physics The capacity of a physical system to do work.

Effect - 1. Something brought about by a cause or agent; a result.
2. The power to produce an outcome or achieve a result; influence:

Thing - 1. An entity, an idea, or a quality perceived, known, or thought to have its own existence.
2.
a. The real or concrete substance of an entity.
b. An entity existing in space and time.
c. An inanimate object.

And I sincerely appreciate your replies. Ignorance sucks like a vacuum.


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Percy
Member
Posts: 18309
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 83 of 248 (599274)
01-06-2011 9:38 AM
Reply to: Message 82 by ProtoTypical
01-05-2011 8:43 PM


Re: Young or old universe
Dogmafood writes:

It turns out that space/time is not fixed,...

Whoa up there just for a moment. Space/time is neither matter nor energy, as per your words and my own understanding of it. It is not a thing until it is defined by other things that really are things like moons and molecules. I have always considered space to be a sort of ‘not a thing’. Fixed or moving or expanding are qualities that belong to things that are subject to relativity. Are they not?

The normal everyday reality in which we live our lives provides relatively infertile ground for drawing analogies to aid our understanding of other less everyday aspects of reality. I think most people would grant that this is true of both space/time and quantum mechanics.

Common analogies for explaining expanding space/time is the surface of an inflating balloon and a rising bread dough, and you've probably already heard these analogies. If it helps you to think of space/time as analogous to things like balloons or bread dough then good, but I think most would agree with you that space/time is not really a thing. I believe Cavediver, and probably most physicists, prefer a more mathematical view. In other words, they use mathematics instead of language to describe space/time and how it behaves. They can't precisely describe space/time in words, but they can use mathematics to describe precisely how it will behave and what will happen.

Why does the red shift that we observe require the expansion of space? Is it because a galaxy that is 13.7 billion light yrs away appears to be receding at a rate greater than c?

If I could rephrase your question, you're asking what evidence we have that tells us that a distant galaxy receding from us at a great rate is actually receding because of the expansion of space and not simply because it is receding from us at a great rate. In other words, how do we know when a velocity is due to the expansion of space versus when it's simply the object's velocity?

Cavediver can probably provide a better answer, but I'll try anyway. When we peer out into space we observe that the more distant a galaxy the greater its recession velocity. One might conclude from this that we're at the center of the universe and that everything is receding from the center, but if you take the recession velocities we measure from the Milky Way and plug them in for some distant galaxy you find that all galaxies are receding from that galaxy, and again with greater velocity with increasing distance. In other words, no matter where you stand in the universe you'll see all galaxies receding at increasing velocities with increasing distance. This could only be true if space itself were expanding.

That's the best I can do for that, I hope Cavediver can do better. If you want to try a Wikipedia explanation then take a look at the Metric expansion of space article, especially the Theoretical basis and first evidence section.

But let me comment about the part where you ask, "Is it because a galaxy that is 13.7 billion light yrs away appears to be receding at a rate greater than c?" First, we will never measure any velocity greater than c. As far as we know, c is a natural constant that governs the maximum rate of influence of any action or effect, including light and gravity.

But second, sufficiently distant objects are receding from us at a rate greater than c, but we only know this from extrapolation of relativity theory and not from direct observation. I do have a vague recollection of reading about indirectly observing such non-observable objects by their light and gravitational effects on closer objects in earlier eras, maybe Cavediver can confirm whether or not I'm misremembering.

Cavediver has warned me off of considering the BB to be like an explosion but I am finding that difficult to do. Is the nature of the universe, on a universal scale, fundamentally different from what I see around me?

As I said at the opening, the nature of the universe on both very small and very large scales is very different from what we experience in everyday life.

--Percy

Edited by Percy, : Grammar.


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Iblis
Member (Idle past 1972 days)
Posts: 663
Joined: 11-17-2005


Message 84 of 248 (599349)
01-06-2011 4:09 PM
Reply to: Message 82 by ProtoTypical
01-05-2011 8:43 PM


Re: Young or old universe
Is the nature of the universe, on a universal scale, fundamentally different from what I see around me?

Yep, that's it.

Spacetime, as it turns out, is a "field", or better yet, an arrangement or "manifold" of "fields". What we call matter and energy, and some other stuff, are actually just "waves" or "disturbances" or "indentations" of these "fields".

I'm putting all these words in quotes in order to emphasize that they don't even mean what they normally mean in spoken language, they are just chosen as the most useful exemplifications of the stuff the math seems to be saying. To be overly dull, the "fields" aren't meadows, the "waves" are very little like water or even sound, even the "particles" aren't little parts at all, at all.

For this same reason, I may have some portion of this explanation "wrong", but I am not overly concerned about that, because even the best explanation that cavediver coughs over here in a bit will only be "more representative", not really truly "right".

We are abusing English, in other words; the proper language is mathematics.


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Taq
Member
Posts: 7673
Joined: 03-06-2009
Member Rating: 2.6


Message 85 of 248 (599367)
01-06-2011 6:23 PM
Reply to: Message 82 by ProtoTypical
01-05-2011 8:43 PM


Re: Young or old universe
Why does the red shift that we observe require the expansion of space?

The following was my lightbulb moment that helped me figure out why the redshifts had to be due to expansion and not velocity through space/time.

Very distant galaxies are heavily redshifted. If this was due to a real velocity through space/time it would take a massive amount of energy to produce this velocity. There really isn't anything to push on when it comes to a galaxy. It would be like pushing on a rope, or pushing on fog. You would need an absolutely massive gravitational force that is somehow spread evenly throughout the galaxy so it can keep it's spiral shape. Any massive object big enough to create these velocities would distort the galaxy beyond all imagination because the side closest to the galaxy (in the direction of the velocity) would experience a much higher gravitational force than the distant side of the galaxy.

On top of that, it would seem like a rather large coincidence that we are sitting in the middle of the show, so to speak. Redshift is the same wherever we look. It is only dependent on the distance between us and the galaxy. If these large redshifts in distant galaxies were due to a real velocity through space/time why don't we see massive redshifts in nearby galaxies, or even galaxies approaching us with a huge blueshift?

So a real velocity through space/time seems to be out of the question. It has to be something else. That something else is the expansion of the space between us and the galaxy.


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cavediver
Member (Idle past 1720 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 86 of 248 (599370)
01-06-2011 7:06 PM
Reply to: Message 82 by ProtoTypical
01-05-2011 8:43 PM


Re: Young or old universe
Space/time is neither matter nor energy... ...I have always considered space to be a sort of ‘not a thing’.

Yes, very much the view outside of the physics/mathematics of Relativity: space(-time) is simply the arena in which "things" are located.

This would be a reasonable view if it wasn't for one feature of space-time: distance. Imagine a simple 2d rectangular grid of points as our simplified "space", say 100 by 100 points. If I have a particle at coordinate (7,14) and another at (10, 18), you would conclude that the distance between the two is 5 units (by Pythagoras.) However, reality is much more complex. Distance is not related to the coordinates. The distance between neighbouring points is actually variable...

Imagine that at each point we have a set of four numbers describing the distance to the four neighbouring points: (2,3,1,0) could mean that the point above is 2 units away, the point to the right is 3 units away, the point below is 1 unit away, and the point to the left is actually zero distance away, making it and our point coincident! So our two points mentioned before could be 5 units apart, but they could be zero distance apart, or they could even be an infinite distance apart! It all depends on the individual distance values. You can hopefully see how our boring flat rectangular grid could in fact have some very interesting geometry when we consider these distances - our grid is becoming curved or warped.

Ok, I'm only part way into this but I have to go... will continue later. Feel free to bring up any questions arising so far.

Edited by cavediver, : No reason given.


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ProtoTypical
Member
Posts: 1775
From: Ontario Canada
Joined: 08-04-2010


Message 87 of 248 (599609)
01-09-2011 9:30 AM
Reply to: Message 86 by cavediver
01-06-2011 7:06 PM


Re: Young or old universe
I just want to make it clear that I am not trying to refute anything you guys are saying. I am trying to understand it.

So the geometry that applies to an eccentric spiral staircase here on earth does not apply to big space. Geometry is not universal.

I find it interesting that the language of mathematics defies translation.


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cavediver
Member (Idle past 1720 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 88 of 248 (599612)
01-09-2011 9:56 AM
Reply to: Message 87 by ProtoTypical
01-09-2011 9:30 AM


Re: Young or old universe
I just want to make it clear that I am not trying to refute anything you guys are saying.

Yes, that is clear. Don't worry, I make it very obvious when I think someone is trying to refute scientific understanding

I went a bit far in my previous reply trying to answer a much larger question than you were asking. The brief version is this: the distances I was describing, these sets of numbers defined at each point in space-time, make up what we call a field.

You are more used to the fields that give rise to the particles: the electrons, photons, quarks, etc. Just about all of physics comes down to interactions between the fields - an electron and an anti-electron annihliating to give two photons is just the eletron field and photon fields exchanging excitations - conservation of "energy" is simply the accounting of the excitations being exchanged.

But those distances form a field which interacts with the particle fields in exactly the same way - we call this the graviton field - and the interactions change the value of the distances, which gives rise to curavture and geometry of space-time. At the fundemental level, fields are just swapping their excitations. At our level, we interpret the particle fields and the graviton field very differently.

So yes, space-time is very much a real "thing", there is a fabric, and it is as fundemental as the particles that make up our everyday experience.


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john6zx
Member (Idle past 2897 days)
Posts: 66
Joined: 01-27-2007


(1)
Message 89 of 248 (600036)
01-12-2011 12:17 AM
Reply to: Message 76 by Iblis
01-01-2011 6:37 PM


IRe: Young or old universe
Look. Has anyone found any science to give evidence that space is a thing? NO! All this talk about expanding space is fantasy unless space is a physical thing. In order to expand a thing has to have physical properties. So what are the physical properities of space?
This message is a reply to:
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Coragyps
Member
Posts: 5377
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 90 of 248 (600058)
01-12-2011 9:14 AM
Reply to: Message 89 by john6zx
01-12-2011 12:17 AM


Re: IRe: Young or old universe
All this talk about expanding space is fantasy unless space is a physical thing....

I refute you thus:

"If you wish to study a granfalloon, just remove the skin of a toy balloon." - Vonnegut, Cat's Cradle


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