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Author Topic:   Starlight
lyx2no
Member (Idle past 4715 days)
Posts: 1277
From: A vast, undifferentiated plane.
Joined: 02-28-2008


Message 31 of 84 (509377)
05-20-2009 11:05 PM
Reply to: Message 27 by riVeRraT
05-20-2009 7:28 PM


Duck! It's M31
Yes, [redshift and blueshift aren't a visible phenomenon] I knew. Like measuring Doppler with sound equipment.
This is kind of fun for me because it as one of the first bits of physics I distinctly figured out for myself. The doppler shift of sound is detectable to the ear because the emitter of the sound; i.e., a horn, emits only a narrow band of the frequencies that we can perceive, while the red and blue shifting of light is not detectable because the emitter of light; i.e. a star, emits a much wider band than the eye can perceive. As a bit of blue light moves toward the violet, and beyond our perception, a bit of green moves toward the blue. This same fill in effect applies all the way down the line where red moving to orange is replaced by infrared moving to red, and into our perception. A horn emitting a range of frequencies between 500-750 Hz can shift a long way in either direction before it moves beyond the ears normal range of 20-20,000 Hz.
I think that is wrong?
Dang! You're just asking for it, aren't you. (Psst! It's not wrong, and you said almost the same thing anyway.)
So it is moving too slowly away from us to measure using Hubble's law.
With the Hubble constant being 71(km/s)/Mps and M31 being 0.784 Mps distant the expansion is 55.7 km/sec. That in itself would be easily detectable; however, M31 is moving toward us at ≈100 km/s due to gravitational acceleration.
What I'd be interested in learning is if the Hubble expansion is taken into account when calculating the timing of our collision with M31.

It is far easier for you, as civilized men, to behave like barbarians than it was for them, as barbarians, to behave like civilized men.
Spock: Mirror Mirror

This message is a reply to:
 Message 27 by riVeRraT, posted 05-20-2009 7:28 PM riVeRraT has replied

Replies to this message:
 Message 32 by riVeRraT, posted 05-21-2009 10:34 AM lyx2no has not replied
 Message 33 by NosyNed, posted 05-21-2009 10:48 AM lyx2no has not replied
 Message 36 by Taq, posted 05-21-2009 12:59 PM lyx2no has replied

  
riVeRraT
Member (Idle past 415 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 32 of 84 (509410)
05-21-2009 10:34 AM
Reply to: Message 31 by lyx2no
05-20-2009 11:05 PM


Re: Duck! It's M31
quote:
Dang! You're just asking for it, aren't you. (Psst! It's not wrong, and you said almost the same thing anyway.)
I think in the last 4 posts and replies to me we are confusing two different topics, or thoughts. I had said the expansion as a result of the big bang of objects in our own galaxy cannot be measured because they are moving with us.
Then I was talking about our local group, and not being able to measure their expansion relative to the universe, not to us.
Onfire: I was taught a long time ago by the administrators to try and combine posts, cause it can get out of hand, and that 300 limit can come up fast. Anyone who is involved in the thread should be reading all posts, otherwise things get repeated.

This message is a reply to:
 Message 31 by lyx2no, posted 05-20-2009 11:05 PM lyx2no has not replied

Replies to this message:
 Message 35 by Percy, posted 05-21-2009 10:56 AM riVeRraT has replied

  
NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 33 of 84 (509411)
05-21-2009 10:48 AM
Reply to: Message 31 by lyx2no
05-20-2009 11:05 PM


Thanks for the Education
This is kind of fun for me because it as one of the first bits of physics I distinctly figured out for myself. The doppler shift of sound is detectable to the ear because the emitter of the sound; i.e., a horn, emits only a narrow band of the frequencies that we can perceive, while the red and blue shifting of light is not detectable because the emitter of light; i.e. a star, emits a much wider band than the eye can perceive. As a bit of blue light moves toward the violet, and beyond our perception, a bit of green moves toward the blue. This same fill in effect applies all the way down the line where red moving to orange is replaced by infrared moving to red, and into our perception. A horn emitting a range of frequencies between 500-750 Hz can shift a long way in either direction before it moves beyond the ears normal range of 20-20,000 Hz.
Hey, thanks lyx2no, I'd never thought about that. I'm happy to have learned a little something.

This message is a reply to:
 Message 31 by lyx2no, posted 05-20-2009 11:05 PM lyx2no has not replied

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


Message 34 of 84 (509412)
05-21-2009 10:55 AM
Reply to: Message 27 by riVeRraT
05-20-2009 7:28 PM


I think that is wrong?
Not a chance
Everything in our galaxy is moving with us
Moving with us where? Don't think of the Milky Way being carried in some direction by the expansion, moving away from some "central" point. As far as we are concerned, the expansion is purely away from us, and we are at the centre of the expansion. Every other galaxy in the Universe thinks the same, and this preserves the symmetry of the expansion.
If M-33/31 are only 2 million light years away, then it has only separated from us very little compared to the 14 billion light years we have traveled from the center.
We have travelled no-where. We have always been at the centre. As has every other galaxy. The centre has just grown quite a bit!
So it is moving too slowly away from us to measure using Hubble's law.
M31 is not moving away at all - it is moving towards us and will collide at some point.

This message is a reply to:
 Message 27 by riVeRraT, posted 05-20-2009 7:28 PM riVeRraT has not replied

  
Percy
Member
Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 35 of 84 (509413)
05-21-2009 10:56 AM
Reply to: Message 32 by riVeRraT
05-21-2009 10:34 AM


Re: Duck! It's M31
Hi riVeRraT,
Some of what you said was expressed in a way where I can't tell if it represents misunderstandings or is just ambiguous, so here's my interpretation of either what you meant, or at least should have meant.
riVeRraT writes:
I had said the expansion as a result of the big bang of objects in our own galaxy cannot be measured because they are moving with us.
The expansion of the universe is not a result of any impetus provided by the Big Bang. Rather, expansion appears to be an inherent property of the universe. And the expansion is not caused by objects moving away from each other within space. Rather, it is caused by the expansion of space itself.
Then I was talking about our local group, and not being able to measure their expansion relative to the universe, not to us.
Space within the local group is expanding, but the galaxies of the local group are sufficiently near one another that gravity is strong enough to keep them from moving along with the expanding space. The force of gravity is not strong enough to keep more distant galaxies from retreating along with the expansion of space, and so they recede from us with increasing velocity with increasing distance.
Onfire: I was taught a long time ago by the administrators to try and combine posts, cause it can get out of hand, and that 300 limit can come up fast. Anyone who is involved in the thread should be reading all posts, otherwise things get repeated.
Combining replies into a single message is usually only suggested by moderators to those who have a tendency to post a bunch of consecutive short replies to many messages.
--Percy

This message is a reply to:
 Message 32 by riVeRraT, posted 05-21-2009 10:34 AM riVeRraT has replied

Replies to this message:
 Message 38 by riVeRraT, posted 05-22-2009 10:37 AM Percy has replied
 Message 39 by riVeRraT, posted 05-22-2009 10:39 AM Percy has not replied

  
Taq
Member
Posts: 9970
Joined: 03-06-2009
Member Rating: 5.6


Message 36 of 84 (509421)
05-21-2009 12:59 PM
Reply to: Message 31 by lyx2no
05-20-2009 11:05 PM


Re: Duck! It's M31
lyx2no writes:
A horn emitting a range of frequencies between 500-750 Hz can shift a long way in either direction before it moves beyond the ears normal range of 20-20,000 Hz.
At the same time, if someone sped past you in a dragster going 350 miles per hour while blowing on a dog whistle would you be able to hear the dog whistle as they sped away?
What I'd be interested in learning is if the Hubble expansion is taken into account when calculating the timing of our collision with M31.
I would assume that the blueshift would give us the actual speed of approach including expansion.

This message is a reply to:
 Message 31 by lyx2no, posted 05-20-2009 11:05 PM lyx2no has replied

Replies to this message:
 Message 37 by lyx2no, posted 05-21-2009 3:46 PM Taq has not replied

  
lyx2no
Member (Idle past 4715 days)
Posts: 1277
From: A vast, undifferentiated plane.
Joined: 02-28-2008


Message 37 of 84 (509431)
05-21-2009 3:46 PM
Reply to: Message 36 by Taq
05-21-2009 12:59 PM


Re: Duck! It's M31
At the same time, if someone sped past you in a dragster going 350 miles per hour while blowing on a dog whistle would you be able to hear the dog whistle as they sped away?
No! Dragsters are really, really loud. You'd not be able to hear anythng.
I would assume that the blueshift would give us the actual speed of approach including expansion.
True. The blue shift will always give the current approach velocity; but, what will be the approach velocity one billion years hence. As M31 gets closer its velocity due to G acceleration will increase, which is easy to account for, while the Hubble expansion will decrease proportionally to the separation, complicating the situation. Does it shift the collision timing away from the easy calculation more then a percentage point or two?
If the dog whistle's stationary frequency is <29 detectable.

It is far easier for you, as civilized men, to behave like barbarians than it was for them, as barbarians, to behave like civilized men.
Spock: Mirror Mirror

This message is a reply to:
 Message 36 by Taq, posted 05-21-2009 12:59 PM Taq has not replied

  
riVeRraT
Member (Idle past 415 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 38 of 84 (509545)
05-22-2009 10:37 AM
Reply to: Message 35 by Percy
05-21-2009 10:56 AM


Re: Duck! It's M31
quote:
The expansion of the universe is not a result of any impetus provided by the Big Bang. Rather, expansion appears to be an inherent property of the universe.
That is not how I learned it. Also the name Big Bang does not lend itself to be considered anything but impetus. I would think it to be logical to assume that there is some force behind the expansion of space, or the universe as we know it. Especially since objects are attracted to each other, something must be driving them apart.
Either way there should be some kind of leading edge (microwave background) and a direction were something is not moving away from us, because there is nothing.
As I read it, we are like dots on a balloon that is being filled with air. If all the stars within our dot are moving with us, we can't measure their expansion relative to the rest of the universe.

This message is a reply to:
 Message 35 by Percy, posted 05-21-2009 10:56 AM Percy has replied

Replies to this message:
 Message 40 by Percy, posted 05-22-2009 1:29 PM riVeRraT has not replied
 Message 41 by onifre, posted 05-22-2009 3:03 PM riVeRraT has not replied

  
riVeRraT
Member (Idle past 415 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 39 of 84 (509546)
05-22-2009 10:39 AM
Reply to: Message 35 by Percy
05-21-2009 10:56 AM


Re: Duck! It's M31
quote:
Combining replies into a single message is usually only suggested by moderators to those who have a tendency to post a bunch of consecutive short replies to many messages.
If that were only the case. If 5 people reply to you, shouldn't it require 5 replies back? That is how I think it should be, yet I was told to do otherwise. I can't believe you just said that, this site continues to amaze me. Bias.

This message is a reply to:
 Message 35 by Percy, posted 05-21-2009 10:56 AM Percy has not replied

  
Percy
Member
Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 40 of 84 (509567)
05-22-2009 1:29 PM
Reply to: Message 38 by riVeRraT
05-22-2009 10:37 AM


Re: Duck! It's M31
riVeRraT writes:
Also the name Big Bang does not lend itself to be considered anything but impetus.
Fred Hoyle coined the term Big Bang as an attempt at derision and the name stuck. The term was never meant to be descriptive. The Big Bang was merely the rapid expansion of the universe from an extremely hot dense state.
Just at the moment of the Big Bang the universe was incredibly tiny, hot and dense. All matter and energy of the universe was contained in a space tinier than an atom. And it was contained in that space not by any container, but simply because that's how big space was. There was nowhere else for matter to be but within that tiny, tiny space.
The Big Bang was actually a very rapid expansion of the size of universe. From a size tinier than an atom the universe rapidly expanded, and the contents of the universe expanded with it. There was never any explosive impetus.
I would think it to be logical to assume that there is some force behind the expansion of space,...
There is, just as you say here, a force behind the expansion of space. We call it dark energy, but we don't really know what it is. But the ongoing expansion of space is not the result of space, or of matter either, being blown outward by the Big Bang.
Especially since objects are attracted to each other, something must be driving them apart.
Nothing is driving them apart in the sense of any repulsive force. Again, it is space itself that is expanding, and it is carrying away with it the matter contained therein, except in cases where the matter is sufficiently dense to hold itself together despite the expanding space.
Either way there should be some kind of leading edge (microwave background)...
There is no "leading edge" to the expansion of space. Space is expanding everywhere. The microwave background radiation arrives from all directions simultaneously everywhere throughout the universe.
If all the stars within our dot are moving with us, we can't measure their expansion relative to the rest of the universe.
That's because they're not expanding, but we can measure the speed with which our local group of galaxies is receding from other local groups. We can't directly measure the expansion of space within the local group, but we infer that it is the same here as it is for everywhere else throughout the universe.
--Percy

This message is a reply to:
 Message 38 by riVeRraT, posted 05-22-2009 10:37 AM riVeRraT has not replied

Replies to this message:
 Message 42 by cavediver, posted 05-22-2009 5:27 PM Percy has replied

  
onifre
Member (Idle past 2950 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 41 of 84 (509579)
05-22-2009 3:03 PM
Reply to: Message 38 by riVeRraT
05-22-2009 10:37 AM


Re: Duck! It's M31
Minor quibble:
Especially since objects are attracted to each other, something must be driving them apart.
Objects are not really attracted to each other, especially not by any "force"; that is old Newtonian physics.
The seemingly attractive nature of gravity is due to mass's affect on space itself, not a force.
If all the stars within our dot are moving with us, we can't measure their expansion relative to the rest of the universe.
The expansion doesn't affect individual stars.
- Oni

"I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks
"I never knew there was another option other than to question everything"--Noam Chomsky

This message is a reply to:
 Message 38 by riVeRraT, posted 05-22-2009 10:37 AM riVeRraT has not replied

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


Message 42 of 84 (509595)
05-22-2009 5:27 PM
Reply to: Message 40 by Percy
05-22-2009 1:29 PM


Re: Duck! It's M31
There is, just as you say here, a force behind the expansion of space. We call it dark energy, but we don't really know what it is.
Careful. Dark energy is merely that which is causing the expansion to accelerate. The expansion would still occur even if there was no dark energy. Expansion is simply what you get with a homogeneous isotropic distribution of mass.

This message is a reply to:
 Message 40 by Percy, posted 05-22-2009 1:29 PM Percy has replied

Replies to this message:
 Message 43 by Percy, posted 05-22-2009 7:06 PM cavediver has not replied

  
Percy
Member
Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 43 of 84 (509607)
05-22-2009 7:06 PM
Reply to: Message 42 by cavediver
05-22-2009 5:27 PM


Re: Duck! It's M31
Yeah, I meant the acceleration of the expansion.
--Percy

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RevCrossHugger
Member (Idle past 5351 days)
Posts: 108
From: Eliz. TN USA
Joined: 06-28-2009


Message 44 of 84 (513698)
07-01-2009 6:08 AM


The other approach is to claim that light speed has slowed down since "Creation Week." A guy named Setterfield spilled lots of ink on proposals for this. Light needs to have moved millions of times faster for this to work, and physics can get to be a problem: Einstien's E=mc2 would indicate that subatomic events like nuclear decay would release a quadrillion times more energy if c, the speed of light, were a million times faster. We don't see this in old stars.
Ha well I am a progressive creationist, but maybe you can say that just as there was a period of inflation (where the universe exceeded the speed of light) Maybe there was a 'time' where light slowed down? The speed of light (c) doesn't have to be constant (its not). I have no math to support the contention of course.
; {>
'When Selfish Gene author Richard Dawkins challenged physicist John Barrow on his formulation of the constants of nature at last summer Templeton-Cambridge Journalism Fellowship lectures, Barrow laughed and said, “You have a problem with these ideas, Richard, because you aren't really a scientist. You're a biologist'
Edited by RevCrossHugger, : No reason given.

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


Message 45 of 84 (513707)
07-01-2009 6:58 AM
Reply to: Message 44 by RevCrossHugger
07-01-2009 6:08 AM


but maybe you can say that just as there was a period of inflation (where the universe exceeded the speed of light)
1) The Universe does not exceed the speed of light, in the same way that roads tend not to exceed speed limits.
2) The only sense that inflation has anything to do with exceeding the speed of light, is exactly the same sense that the normal everyday expansion of the Universe 'exceeds the speed of light' - so inflation has nothing to do with what you are trying to say.
3) Inflation covers a huge body of work, from original hypothesis, through multiple theories, and onto the discovery of compelling evidence consistent with a number of the theories; where-as...
The speed of light (c) doesn't have to be constant (its not).
is your own wishful thinking. The speed of light has not measurably changed* in the past 13 billion years, and we can tell this from direct observation. You quote Barrow, so have a look at his own work on the possible variation of alpha* over the course of the Universe.
*when I speak of changing the speed of light, I'm implying a changing alpha.

This message is a reply to:
 Message 44 by RevCrossHugger, posted 07-01-2009 6:08 AM RevCrossHugger has replied

Replies to this message:
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