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Author Topic:   The accelerating expanding universe
Taz
Member (Idle past 3291 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 16 of 149 (550570)
03-16-2010 12:08 PM
Reply to: Message 15 by cavediver
03-16-2010 9:34 AM


I'm curious. What is your best guess on the on-going "push"? I've heard some guesses out there. Just wanted to know yours.

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(1)
Message 17 of 149 (550590)
03-16-2010 3:44 PM
Reply to: Message 16 by Taz
03-16-2010 12:08 PM


What is your best guess on the on-going "push"?
Just another field - almost certainly scalar - with appropriate density and pressure. There is a problem with both the name Dark Energy, and the way it is presented, in that the suggestion is that we have absolutely no clue as to the nature of this mysterious substance. The truth is that we are "baffled" by Dark Energy in much the way that marine biologists are "baffled" by newly-found deep-sea creatures. They exceed expectations in weirdness and defy some previously held thoughts - but they don't need us to re-write physics, only a bit of biology. Dark Energy certainly extends our view of the Standard Model of particle physics, but it's par for the course for those of us in theoretical fundemental physics research.

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gragbarder
Junior Member (Idle past 4917 days)
Posts: 30
Joined: 03-19-2010


Message 18 of 149 (551130)
03-21-2010 9:15 AM
Reply to: Message 1 by Hoof Hearted
03-13-2010 4:40 AM


Several problems with the science in many comments.
1. The Hubble "constant" is constant across space, but not across time.
That is why the expansion history of the universe is not linear, with a recent acceleration. I mean, how could the expansion rate have started increasing some 5 billion years ago if the expansion rate is always constant?
2. Very distant galaxies can recede from us at a speed greater than c.
The very distant, receding galaxies are not moving through space at a speed greater than c: they are essentially at rest, being carried away by the expansion of space between us and them, and there's no theoretical limit on how fast space itself can expand.

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ramoss
Member (Idle past 612 days)
Posts: 3228
Joined: 08-11-2004


Message 19 of 149 (557426)
04-25-2010 1:34 PM
Reply to: Message 17 by cavediver
03-16-2010 3:44 PM


I was wondering.. could dark energy be nothing but the Casimir effect on a grander scale?

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lyx2no
Member (Idle past 4716 days)
Posts: 1277
From: A vast, undifferentiated plane.
Joined: 02-28-2008


Message 20 of 149 (557555)
04-26-2010 4:39 PM
Reply to: Message 19 by ramoss
04-25-2010 1:34 PM


Dark Energy ≠ Casimir Effect
The Casimir effect is caused by there being a greater, net electromagnetic field external to the two, closely spaced plates due to the internal exclusion of virtual photons with wave lengths longer than the distance between the plates.
What would be the analog for the plates, the space between the plates and the space outside the plates in the open Universe?

"Mom! Ban Ki-moon made a non-binding resolution at me." Mohmoud Ahmadinejad

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ramoss
Member (Idle past 612 days)
Posts: 3228
Joined: 08-11-2004


Message 21 of 149 (557586)
04-27-2010 12:42 AM
Reply to: Message 20 by lyx2no
04-26-2010 4:39 PM


Re: Dark Energy ≠ Casimir Effect
If you look at space at distances of less that 10^ -30 cm, space starts becoming 'rough', and boils into quantum foam at a length of 10 ^-33 cm..
So the analogy to the plates would be space itself, since space is not completely smooth..

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lyx2no
Member (Idle past 4716 days)
Posts: 1277
From: A vast, undifferentiated plane.
Joined: 02-28-2008


Message 22 of 149 (557731)
04-27-2010 6:24 PM
Reply to: Message 21 by ramoss
04-27-2010 12:42 AM


Re: Dark Energy ≠ Casimir Effect
But electromagnetic fields don't know space isn't smooth. The shortest route for a photo from one crest to the next is under the trough. It can't travel in what the common mental model of 'rough' space looks to be a straight line. Take Cape Cod as an example. For a landlubber the shortest distance between Plymouth Rock (Plymouth, MA) and Pilgrim Monument (Provencetown, MA) is 76.1 miles, while for a mariner it only 21.9 knots (25.2 miles). Electromagnetic fields are spacelubbers and don't transect the non-space.
Plus that, the excluded virtual photons in your model would have to have wavelengths less than 10-30 cm. That implies a mass equivalence greater than that of the bananas eaten daily in that coal-scarred city where children play without despair (30,000 lbs.)
AbE: That first sentence is really badly worded. If ya'll can find your way to ignoring it it would be greatly appreciated.
Edited by lyx2no, : No reason given.

"Mom! Ban Ki-moon made a non-binding resolution at me." Mohmoud Ahmadinejad

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 23 of 149 (557811)
04-28-2010 3:39 AM
Reply to: Message 22 by lyx2no
04-27-2010 6:24 PM


Re: Dark Energy ≠ Casimir Effect
AbE: That first sentence is really badly worded. If ya'll can find your way to ignoring it it would be greatly appreciated.
Oh dear - I thought it was actually the best (most understandable) bit
And knots are a velocity, not a distance - nautical miles are abbreviated to nautical miles

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ramoss
Member (Idle past 612 days)
Posts: 3228
Joined: 08-11-2004


Message 24 of 149 (557884)
04-28-2010 12:26 PM
Reply to: Message 22 by lyx2no
04-27-2010 6:24 PM


Re: Dark Energy ≠ Casimir Effect
Are virtual particles an 'electromagnetic field'??

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 25 of 149 (557891)
04-28-2010 12:48 PM
Reply to: Message 24 by ramoss
04-28-2010 12:26 PM


Re: Dark Energy ≠ Casimir Effect
Are virtual particles an 'electromagnetic field'??
An EM field can be described as being made up of virtual particles (photons, electrons, positrons) - virtual particles don't exist as such, they are simply fourier modes that make up the larger field configuration. But just as fourier modes of a sound signal are easier to deal with than the complex sound signal itself, so too are virtual partciles easier to calculate with than the full field configuration.

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lyx2no
Member (Idle past 4716 days)
Posts: 1277
From: A vast, undifferentiated plane.
Joined: 02-28-2008


Message 26 of 149 (558098)
04-29-2010 8:07 PM
Reply to: Message 23 by cavediver
04-28-2010 3:39 AM


128 Bit Encryption
Oh dear - I thought it was actually the best (most understandable) bit
The reason I second guessed myself was that I could just hear the likes of you reminding me of lensing or some such. I meant to get around to explaining myself before the day was done but got busy again. Anyway, what I meant was that the fields follow the shape of space never encountering an edge that they might press against. Adding here that electromagnetic fields don't press against space at all, at all. A photon wouldn't get too far if it had to push space out of its way.
Further, as I was calculating the energy of a photon with a wave length of 10-28 meters I ran through the value-units: eV, Joules, Kelvin, Wattever I discovered it had a value right at 30k when pounds were the unit, which brought to mind the folk song 30,000 pounds of bananas. I figured if anyone was curious they'd google the coal-scarred city. That's what I do instead of scratching my head now-a-days.
And knots are a velocity, not a distance - nautical miles are abbreviated to nautical miles
And what's worse is that I know that.
Edited by lyx2no, : spelink.

"Mom! Ban Ki-moon made a non-binding resolution at me." Mohmoud Ahmadinejad

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Nuimshaan
Member (Idle past 4953 days)
Posts: 18
Joined: 08-11-2010


Message 27 of 149 (575082)
08-18-2010 8:41 PM


It is generally accepted that when two hot bodies of matter seperate themselves from one another...a generall cooling effect is noticed.
IF the stars are moving away from each other, then overall, there is a loss of heat. This equals loss of energy.
Spread out all of the stars one from another....this world will cool off, thusly stopping any expansion thereafter.
Thank you, Nuimshaan

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crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 28 of 149 (575084)
08-18-2010 8:44 PM
Reply to: Message 27 by Nuimshaan
08-18-2010 8:41 PM


It is generally accepted that when two hot bodies of matter seperate themselves from one another...a generall cooling effect is noticed.
This is something you've made up.

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break
Junior Member (Idle past 4215 days)
Posts: 2
Joined: 12-23-2010


Message 29 of 149 (597664)
12-23-2010 6:18 AM


Hi, first post on EvC forums.
I was hoping that CaveDiver - or anyone else - could answer a question I have regarding the expansion of the Universe.
My understanding so far is that the Universe is not expanding because all objects are explosively speeding away from each other but rather, because space itself is expanding.
So my question would be, how do we know this ? How can we tell space itself is expanding ? What observations led us to this conclusion ? What is the difference between objects speeding away from us and objects being mostly stationary inside an expanding space and how can we tell the later than the former is what is happening in our universe ?
Thanks in advance for your replies.
Edited by break, : No reason given.

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frako
Member (Idle past 305 days)
Posts: 2932
From: slovenija
Joined: 09-04-2010


Message 30 of 149 (597667)
12-23-2010 7:17 AM
Reply to: Message 27 by Nuimshaan
08-18-2010 8:41 PM


It is generally accepted that when two hot bodies of matter seperate themselves from one another...a generall cooling effect is noticed.
HAHA ORLY
So if i drive my car west and my girlfriend rives my other car east we would not need air conditioning cause the cars would get cold on their own
I think you got some things mixed up yes it is true that if something moves on its own power it slowly looses its power/energy (in some cases heat) the reason why you need to fill up your gas tank every once in a while. Tough that is not the case here.

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