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Author Topic:   Did the expansion rate of the universe exceed lightspeed?
Percy
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Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 3 of 86 (458644)
03-01-2008 11:28 AM
Reply to: Message 1 by Explorer
02-26-2008 8:55 PM


You're talking about inflation, an hypothesized period during which the early universe grew in size at an enormous rate often described as exceeding the speed of light. Inflation is the expansion of space itself, which is not limited by the speed of light. Inflation has nothing to do with the motion of matter and energy through space, which can't exceed the speed of light.
We don't really know what was happening to the universe when it was younger than T=10-43 seconds. Before that time the density of the universe was greater than the Planck density, which means there was more energy than could fit into the space available under physical laws as currently understood.
But we have a pretty good idea about what happened after T=10-43 seconds, and we're pretty sure the physical laws we know and love today were already in force, to the extent we comprehend them. Cavediver can correct me if I'm wrong, but I believe T=10-43 seconds marks the beginning of inflation, during which the size of the universe doubled roughly every 10-34 seconds. By T=10-32 seconds inflation was over and the universe had doubled in size at least 100 times.
Since physical laws were in force during expansion, no matter or energy traveled faster than the speed of light. But as I said earlier, inflation is often described as a period in the early universe where space (not matter or energy) expanded faster than the speed of light. In other words, the volume of space expanded faster than the speed of light, not the matter and energy within that space.
Cavediver will, I hope, correct me if I've got this wrong, but I take issue with the description that space expanded faster than the speed of light. While it is true that some parts of the inflationary universe were receding from each other at relative speeds greater than light, this is also true today. Space itself is not expanding that fast today, and it was not expanding that fast during inflation. A doubling in size every 10-34 seconds means, for example, that two points in space separated by a single Planck distance, which is 1.6 10-35 meters, would in a mere 10-34 seconds become separated by twice that distance. Dividing the change in distance by the change in time yields 0.16 meters/second, which is far less than the speed of light.
--Percy

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Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 21 of 86 (458793)
03-02-2008 9:17 AM
Reply to: Message 19 by Straggler
03-02-2008 8:09 AM


Re: Speed of Light
Straggler writes:
I thought the limit of the speed of light was related to the increase of an objects mass as it approaches the speed of light and that at the speed of light the mass would be infinite thus requiring infinite force to accelerate it further.
You're correct that this is why you'll never observe anything moving faster than the speed of light.
But Cavediver's example of traveling light years in just days *was* very confusing. How could this be if you can never observe anything traveling faster than the speed of light? Well, the answer is that time is relative, too.
Let's add more detail to Cavediver's example and say that there are two stars 10 light years apart, call them A and B, and that you are at some other star observing a friend travel from A to B. You observe him leave star A toward star B and accelerate faster and faster to .9 the speed of light, then .99 the speed of light, then .999 the speed of light. He keeps going faster and faster and getting closer to the speed of light, but never reaching it. Then, when he's halfway between the two stars he begins decelerating, finally reaching a speed of zero when he reaches star B.
You observe that it has taken your friend 11 years to go 10 light years, and so deduce that he's traveled at an average speed of .9 c in your reference frame.
But let's say that you have a very good telescope and are able to observe your friend's clock. What you discover is that during the journey his clock was moving much more slowly than your own, and that after 11 years on your clock only a year had gone by on your friend's clock. It would appear to you that your friend would think he has traveled 10 light years in just a year, and that therefore there must have been periods during his journey when he observed his own speed as being much greater than the speed of light.
But relativity still survives intact, and that's because no one can ever observe anything traveling faster than the speed of light, including your friend during his journey. The reason for this is that objects and distances shrink in size in the direction of observed motion, so as your friend accelerates to near the speed of the light, the distance he measures between the two stars becomes smaller and smaller. So although his clock says only a year has passed, the distance he has measured himself actually traveling is not 10 light years but perhaps only .9 light years. Since he took a year to travel .9 light years, he would not think his speed ever exceeded the speed of light.
Now if you were to do something invalid, such as use the clock from your friend's reference frame to measure the rate of motion across distances measured in your own reference frame, then you'll get bogus results that say he is traveling faster than the speed of light. One should never combine measurements from different reference frames without making the necessary relativistic adjustments.
--Percy
Edited by Percy, : Typo.

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 Message 19 by Straggler, posted 03-02-2008 8:09 AM Straggler has replied

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Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 22 of 86 (458798)
03-02-2008 9:27 AM
Reply to: Message 20 by Explorer
03-02-2008 8:26 AM


Re: Speed of Light
Hi Explorer,
I'm no Cavediver, but let me try to tackle just this portion:
Explorer writes:
Lets say that the matter in the universe at some point in time creates enough gravity for a "global" gravity-hole (big crunch scenario) that makes all the matter in the universe travel towards that hole. Even when it does the expansion of "space" wouldn’t stop as I understand it? It would be a battle of some kind between the "space-expansion" and the gravity force. Wherever that leads us...
I hope this isn't too far off, at least at a simplistic level, and as always Cavediver can correct me if I'm wrong, but the short answer is that the forces of gravity cancel out.
An analogy would be the gravity you would experience at the center of the earth. Since there are equal amounts of matter in all directions pulling equally on you, you would experience no gravity and would have zero weight at the earth's center.
Even though the very early universe was incredibly dense, certainly sufficient to produce a black hole, it was incredibly dense everywhere throughout the universe. This means the net gravity at any given point in the early universe was the same, approximately zero, since equal amounts of matter existed in all directions.
--Percy

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 Message 45 by LucyTheApe, posted 03-04-2008 10:43 AM Percy has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 46 of 86 (459149)
03-04-2008 11:04 AM
Reply to: Message 45 by LucyTheApe
03-04-2008 10:43 AM


Re: Speed of Light
First, note Cavediver's correction to my description. While the net effect on an actually particle would be nil, space/time was still curved to essentially the same high degree everywhere.
Second, just as there's no center to the universe today, there was no center to the universe at the Big Bang, either. No matter which point within the Big Bang you choose, there were equal amounts of space stretching off in all directions.
If you're having trouble imagining a tiny pea-sized and rapidly expanding Big Bang that actually has no edges, you're not alone. Maybe someone can suggest a useful visualization.
--Percy

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Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 55 of 86 (459365)
03-06-2008 11:37 AM
Reply to: Message 53 by lyx2no
03-06-2008 10:43 AM


Re: Did the expansion rate of the universe exceed lightspeed?
In other words, the universe expands 6 billionths of a percent per year. Did I do the math right, because that actually sounds like quite a bit. It means a fifth of a mile per year is added per distance to Pluto, though of course the distance itself doesn't change since Pluto is gravitationally bound to the sun.
--Percy

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 Message 53 by lyx2no, posted 03-06-2008 10:43 AM lyx2no has replied

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Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 59 of 86 (460243)
03-13-2008 3:38 PM
Reply to: Message 57 by LouieP
03-13-2008 12:14 PM


Re: Speed of Light
LouieP writes:
if from your frame of reference you were going .500 the speed of light, and .500 in the time direction(your frame of reference would be the speed of light, also what you describes as 45 degrees.)
You're making a simple geometric error. In a simple x/y coordinate system where the length of a line is 1 with one end at the origin and pointing in any direction into the positive quadrant, when the x and y coordinates are equal they are not .5 but .707.
--Percy

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Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 69 of 86 (460350)
03-14-2008 11:30 AM
Reply to: Message 68 by ICANT
03-14-2008 10:57 AM


Re: acceleration
ICANT writes:
If expansion as has been explained to me several times is true.
Everything is fixed with nothing moving only space expanding between those fixed objects
For the umpteenth time, nobody said nothing is moving. It's just that local motions are very tiny when compared to the expansion of space when measured between distant points.
Let's go back to the balloon analogy. The expanding 3-dimensional universe is analogous to the 2-dimensional surface of an expanding balloon as it is being inflated. Imagine that it's a really, really big balloon and that we can inflate it infinitely. On the surface of this balloon are tiny, tiny mites walking around. The mites are living, and so the blood within them is also moving around. So not only is the blood moving around within the mites, the mites are moving around on the surface of the balloon, and the balloon is expanding.
Two mites that are close together will easily be able to approach each other, because there's only a little bit of balloon material separating them, and they can move faster than the balloon is expanding.
But two mites that are far apart on the balloon might have trouble approaching each other if the distance is great enough, because the more balloon material separating them the faster they move apart because of the expansion of the balloon. Two mites sufficiently far apart would be receding faster than the maximum speed at which they can move and would never be able to make contact.
Note that the speed with which distant mites are receding from each other has little to do with the speed or direction at which they are walking, because the expansion speed is so much greater than their own.
The blood moving around within the mites is analogous to the stars moving around inside galaxies, and the mites moving around on the surface of the balloon are analogous to galaxies moving around within the universe. Just as the mites are slowly moving around on the surface of the balloon, the galaxies are slowly moving around within the universe. And just as the mites motion is tiny compared with the expansion of the balloon when measured across distant parts of the balloon, the galaxies' local motion is dwarfed by the expansion of the intervening space between distant galaxies and isn't a significant factor, which is why it usually isn't mentioned.
--Percy

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 Message 68 by ICANT, posted 03-14-2008 10:57 AM ICANT has replied

Replies to this message:
 Message 70 by ICANT, posted 03-14-2008 11:57 AM Percy has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 71 of 86 (460355)
03-14-2008 12:05 PM
Reply to: Message 70 by ICANT
03-14-2008 11:57 AM


Re: acceleration
ICANT writes:
Now am I to understand our entire galaxey moves around, or is it stationary with space expanding between it and all the other galaxies?
In the balloon analogy, the mites walking around on the surface of the balloon were analogous to the galaxies moving around within the universe, so yes, of course, our galaxy is moving. And so is the nearby Andromeda galaxy. The Andromeda and Milky Way galaxies are on a collision course with an estimated time of impact about 2.5 billion years from now.
--Percy

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 Message 70 by ICANT, posted 03-14-2008 11:57 AM ICANT has replied

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 Message 72 by ICANT, posted 03-14-2008 12:48 PM Percy has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 73 of 86 (460362)
03-14-2008 1:04 PM
Reply to: Message 72 by ICANT
03-14-2008 12:48 PM


Re: acceleration
ICANT writes:
Since they are 2.5 billion light years apart and are expeced to collide in 2.5 billion years. That means that they are traveling at light speed toward each other.
You're off by a factor of a thousand - the Andromeda galaxy is only about 2.5 million, not billion, light years away. The two galaxies are approaching each other at about 1/1000 the velocity of light.
The Andromeda and Milky Way galaxies are so close together that the expansion of space between them is not significant in comparison to their local motions, plus they are gravitationally bound to each other, meaning that the expansion of space in such close quarters is too small too pull them apart. Galaxies must be separated by much, much greater distances before the expansion of space becomes a significant contributor to their apparent relative motion.
For a simple visualization of what our local region of the universe looks like with respect to galaxies, imagine you're in room with DVD disks floating around at random that are separated by an average of about six feet. They're moving very slowly relative to the size of the space they occupy, as it will take the two DVD's that represent the Andromeda and Milky Way galaxies about 2.5 billion years to close the intervening 6 feet.
--Percy

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Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 76 of 86 (460384)
03-14-2008 3:50 PM


Question About Expansion Rate and Clocks
Consider two hypothetical galaxies, both receding from us at the same enormous speed of, say .9c, but one is relatively nearby and the other is on the other side of the visible universe. This means that the nearby one has an enormous velocity through space relative to ourselves, and the distant one has a small velocity through space relative to ourselves that can be ignored but an enormous velocity due to the expansion of space.
Naturally they'd both have the same amount of time Doppler effects, but wouldn't the nearby galaxy experience a large relativistic time dilation relative to ourselves and the distant one not?
If so, then this would mean that Halton Arp is not just wrong, he's nuts. I'm thinking about Arp's contention that galaxies with high red-shift values are actually relatively local objects with high recession speeds that have been ejected from galaxies. Now in addition to the incredibly unlikely coincidence that everything ejected from galaxies is ejected away from us, there's the impossibility that they're close objects because the time dilation effects are way too small.
Apologies if I'm way off the mark, be gentle, my misconceptions are hard earned.
--Percy

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 Message 80 by cavediver, posted 03-14-2008 5:41 PM Percy has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 81 of 86 (460407)
03-14-2008 8:03 PM
Reply to: Message 80 by cavediver
03-14-2008 5:41 PM


Re: Question About Expansion Rate and Clocks
Oh. Darn. Well, Arp's still an idiot.
There was a contributor named Sylas here starting back in 2004, and he was our cosmological expert for a while. He's been gone for a while, but it was something he said that led me to my incorrect conclusion. I'll poke around for a bit and see if I can dig it out, I'd like to clear up how I picked up the wrong impression. Thanks for the info!
--Percy

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Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 82 of 86 (460410)
03-14-2008 8:36 PM
Reply to: Message 80 by cavediver
03-14-2008 5:41 PM


Re: Question About Expansion Rate and Clocks
I found the Sylas post, it was Message 226. This is embarrassing because it reveals that the passage of time seems to have brought my mind back around to my earlier misunderstanding.
Anyway, that old thread was discussing a different topic but Sylas and I were touching on the same point as here. I think the discussion about the Doppler contributions must have confused me. Why did he mention them in the first paragraph, then say it's one of the lines of evidence that tells us the redshift is due to the expansion of space in the next?
Relative to ourselves, wouldn't the time dilation due to relativistic contributions be the same for a moving object regardless of the direction of its velocity vector? And then there's an additional Doppler effect that's a function of how much of the velocity vector is parallel to the distance vector? And how do we figure out which contribution is which for distant objects?
Hope you and Son Goku never get tired of answering dumb questions.
--Percy

This message is a reply to:
 Message 80 by cavediver, posted 03-14-2008 5:41 PM cavediver has replied

Replies to this message:
 Message 83 by cavediver, posted 03-15-2008 6:59 AM Percy has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 84 of 86 (460489)
03-15-2008 4:36 PM
Reply to: Message 83 by cavediver
03-15-2008 6:59 AM


Re: Question About Expansion Rate and Clocks
cavediver writes:
So Arp still has to explain why all his galaxy-associated high-velocity quasars are all heading away from us!!
This has puzzled me for a long time, how someone so obviously brilliant could be so wrong, so I just looked into this a little bit more. Information is sparse, but it appears that a survey of the local group reveals that all eleven companion galaxies have a redshift relative to their parent galaxies (is this true?), when it should be roughly 50%.
From this Arp concludes that the observed red-shift of galaxies is intrinsic. Intrinsically red-shifted objects have lower mass than local matter because they're made up of particles with lower mass. They have low mass because they are new matter forged in the center of galaxies, and matter increases in mass over time.
But ferreting out these details doesn't diminish in the slightest how incredibly far fetched this all is. You'd think he would long ago have tired of his work never finding any additional observational or experimental support. Indeed the opposite occurs, as each year improving astronomical tools disprove more and more of his supposed anomalies, and more weight is added to the evidence against his ideas. He must be a very odd bird.
--Percy

This message is a reply to:
 Message 83 by cavediver, posted 03-15-2008 6:59 AM cavediver has replied

Replies to this message:
 Message 85 by cavediver, posted 03-15-2008 7:30 PM Percy has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 86 of 86 (460516)
03-15-2008 9:03 PM
Reply to: Message 85 by cavediver
03-15-2008 7:30 PM


Re: Question About Expansion Rate and Clocks
cavediver writes:
I've just perused the fourteen companions of M31 listed on Wiki - seven are higher z than M31, five on lower (more negative z), and there is no data for two. Hmmm...
But is Arp so perverse, so taken with his own theories, so nuts, as to make up data?
The source of the claim that all eleven companion galaxies in the local group have redshifts greater than their parent galaxies comes from reviews of Arp's 1998 book Seeing Red. For example, this is from a review by Tom Van Flandern:
Companion galaxies in general seem to have net redshifts that exceed that of their parents. All eleven companion galaxies in the Local Group have redshifts with respect to their parent, the Andromeda galaxy in the center of the group. Likewise, all eleven companion galaxies of the neighboring M81 group have redshifts relative to M81. Yet, if these companions were orbiting their parent galaxy, roughly 50% of them ought to have been blue-shifted. Although the evidence for companion redshifts is less definitive for more distant galaxy groups, it is still statistically significant. Excess redshifts over blueshifts for companion galaxies relative to their parents is apparently a verifiable feature of the local universe. And that means the redshift must have some cause other than velocity.
This is really just made up? I mean, sure Arp is wrong and all that, but is he a liar? Delusional? What?
Sorry, rhetorical questions, I know, but what an unfathomable mystery and waste of an incredibly promising career, plus there's all the ammunition he provides to kooks.
--Percy

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