But we're not talking about a duration of radiation in a certain area, but integrating the total number of encounters. If you hang your head outside of a car and open your mouth, you'll swallow twice as many gnats going at 60 mph than you would at 30 mph (if the gnat density is constant in space).
I don't think this is right. First of all, cosmic rays are particles, not radiation (as I think you are implying). But to the point, you would expect to collide with more cosmic rays since you are sweeping out a greater volume due to your velocity. Given some cosmic ray density in space (number of particles per m^3), the greater the volume swept out, the more encounters there will be. Each encounter would still feature relative velocities less than c.
As an example, in my previous job for a weather company, we'd generate large images of geographic data for a certain area of interest, and separately generate radar or satellite or lightning maps over the same area. We'd then use ImageMagick to combine all the separate images together, along with further generated warning areas, icons, and forecasts representing weather phenomena of interest (tornadoes, mesocyclones, hurricanes) and usually some sort of written annotation (time of image, source). ImageMagick was/is really useful.
Ok, I haven't been keeping up --- this Japanese machine is, I gather, massively parallel. Suppose I wanted to find out which single processor was the speed king for floating point calculations. Is it as simple as sorting for the highest number on SpecFP2000?
Yeah, it's too bad the focus of the submitter was on the Intelligent Design snippet --- probably the least interesting bit in the article. The most fascinating stuff to a non-specialist like me was the complexity in the genetic code. Much more complex, I gather, than other members of the virus family so far discovered, and in fact sharing some genetic coding with "higher" animals? Wow --- that kind of thing really illusrates what makes science so fascinating.
It's quite clear that there's little room for speculation. In the future we may find out that the redshift which you pooh-pooh with such veracity has a much more complex effect than is currently known. At one time the earth was flat, the atom was unsplittable, and a photon could not possibly be both a wave and a particle.
Well, there's little room for *wild* speculation, as any speculation as to the physical causes of redshift must correspond to mountains of previous data and theory on the topic. Speculate all you want, just be prepared for others more acquainted with the science to tell you where you're off track. And I have no idea where you get the notion that I "pooh-pooh" redshift. It was observed with a value of 3.3%. What's the disagreement? Redshift *is* an effect, not a cause. I just don't follow you.
Clearly you know everything there is to possibly know about astronomy.
Now that's just snarky. You're better than that.
I don't have your email, but if you're still interested, here is the link to the initial observational announcement with the 3.3% reshift cited from the observations: Announcement
and here's a link to the Astronomy Picture of the Day with photos of the relevant portion of the sky, as well as many related links: APOD discussion
Now you're agreeing with the sentiment which I expressed after fighting with me for six hours. Truly remarkable.
Well, I mean that cosmology and the phenomenon of redshift is, in general, fascinating. So much so that I decided to make it my vocation. In this case, redshift is not much of a factor in the original story, as opposed to your original statements. Who's fighting? I was just trying, unsuccessfully, to point out a common misunderstanding. Carry on with your views if you take such offense at dissent.
Use of the word "terribly" leads me to believe that you're talking down your nose more than you're trying to hold a productive discussion. If that was your intent then, by all means, carry on.
"Terribly," a colloquialism meant to indicate interest to a high degree. I have a hard time imagining things much more deeply interesting than cosmology.
I don't remember there being a source which said that cosmological redshift is 3 (or 3.3)%. That was your personal assertion.
I think it's buried in the original press release or preprint. Anyway, the standard method we use to determine distances like 440 million ly is the Hubble Law --- observe the redshift and then ham-handedly use the classical Doppler formula z=v/c to get the recessional velocity. If the Hubble constant is, say, 50 km/s/Mpc, then we can get the distance of the object. This works ok for reshifts less than 0.1 or so. Working this out for 440 million ly gives a reshift of about 0.03, similar to other galaxies at that distance (like those in the Coma cluster).
You keep saying that the page I linked to is a common misconception but you offer what to back that up? Since this morning I've looked over at least a dozen pages, all of them physics.edu or space related.gov research (No, I wasn't about to look at answers.com or about.com for a scientific discussion) and all of them, if they include mathematical derivations, use the same equations. So what exactly is this common misunderstanding?
I would recommend a scientific discussion. The misunderstanding is in ascribing the redshifts of distant galaxies to an actual recessional velocity through space. If this were the case, then one could use the classical or relativistic Doppler formulas, like the ones to which you linked. But galaxies can be thought of as basically pinned in an expanding space that carries them along for the ride, like points on an expanding rubber band. The points don't move relative to their local position on the rubber band, but as the band stretches they are carried apart from each other.
What exactly am I wrong about? That the redshift phenomena is something interesting to think about? Do you hold some intellectual astroturf on someone else thinking about the effect of redshift? I see in one of your other posts that you assert that you're an astronomy educator. Perhaps you could contribute something educational rather than repeating,"No! You're wrong! I know all about it but I'm not going to describe it at all. Quit thinking about it!"
You're too touchy. I have attempted to describe it twice. Think about it all you want. It's terribly interesting. Most of the good introductory books on astronomy have cosmological disclaimers like the above, some with stronger language than others. The best book for non-specialists about cosmology ever written, in my opinion, is Harrison's "Cosmology: The Science of the Universe". Sometimes it's available via Amazon. But for a discussion of this, try Wiki Redshift
I can't tell if you're attempting to assert that the redshift phenomena doesn't exist or if you just want to argue about which kind of redshift I was originally thinking about (Doppler, gravitational, cosmological). I was musing about the cumulative effect of all three and how significant it may be. There's clearly a quantifiable effect. Where does your 3% number come from anyway? It's still significant even if it is only 3%.
Try kicking your dog if you need to assert your superiority. I was looking for a productive discussion and apparently I fished out someone who wanted to fight.
I think you took my comments badly. Of course redshifts exist. The kind of redshifts we ought to be talking about are cosmological --- these are the ones typically used in computing distances to galaxies. My 3% number is simply the cosmological redshift (I think in the original source they claim 3.3%), which indicates an expansion of the universe of 3% since the signal was emitted. Then you offered an argument based upon a link to a page that suffers from a common misunderstanding, which I pointed out.
You are right that redshifts, in general, distort the timing of distant events. But here, since the redshift is only 3%, the event (locally, at emission) happened only 3% faster. It's not much of a factor, as I was trying to say. If having a "productive discussion" means that I shouldn't point out where you're wrong, then I'll butt out.
3% over what increment? If it's 3% per light year, or even 3% per 100 light years, or 3% per 100 million light years, then the iteration is definitely significant. Since astronomers rely on red shifting to measure distances between stars within our own galaxy, though, it stands that the impact is significant. I'm not saying it's an issue. I don't want to debate it. I said it's a consideration to think about.
Cosmological redshift is an indicator of how much the universe has expanded since the radiation was emitted. A redshift of 3% (in this case) means that the universe is now 3% bigger than it was when the light was emitted. In fact, that's *all* the redshift means. Cosmological redshift is completely different from the Doppler shift used, as you say, for motions of stars in our own galaxy.
According to this page a red shift of z=4.25, a recession speed of 0.93c, corresponds to a distance of 12-15 million light years. Nine years ago when I was studying nuclear physics I could probably have told you more distinctly what that means. Assuming it's the velocity remaining, a 7% decrease equates to 12-15 million light years. Assuming a linear relationship (unlikely, but I'm doing the math in my head) then light traveling 440 million light years would experience a decrease of around 250%. That means the gamma rays, by the time they reached Earth, are 2.5 times lower in energy than from the originating point. That's not an order of magnitude but it's definitely significant.
Unfortunately, the linked page is in error. It is a common misunderstanding. Astronomers rarely speak of a "distance" of 12-15 billion light years, because such a distance has no meaning. Is it 12-15 billion ly from the time of emission or reception? And applying special relativistic Doppler shifts is in error since the expansion is for co-moving objects carried along by the expansion of *space*. Galaxies are not rushing through space away from us, but are fairly fixed in an expanding space. It is a subtle, but crucial, difference. The *only* information accurately obtained via cosmological redshifts is the expansion factor. Calculating a lookback time or distance (emission or reception) to an object requires a certain model of expansion that has occurred in the meantime.
Obviously they get compressed together over a long journey. Has anyone considered this?
A great many people. And it runs the other way --- radiation gets spread out due to cosmic expansion over a long journey, so we actually see the phenomena in slow motion.
Then there's timing. Red shifting would cause the duration of an emission to expand as well. If most GRBs, after traveling billions of years, only last a few seconds then the event which caused the emission must be on the order of a few milliseconds (or arbitrarily "less than a few seconds"). This burst was 440 million years off and lasted 33 minutes. The amount of red shifting would be significantly less between 440 million years and several billion... so the originating event could still have been on the order of whole minutes long (or arbitrarily "more than as much less than 33 minutes as a few seconds is to a few milliseconds").
The redshift is only about 3%, so probably not an issue here.
Right, but the result of the initial observation is still not deterministic, so you can't use non-locality to send information. At least according to the Copenhagen (most widely held) interpretation of QM.
This is a good exercise in drawing distinctions between cows and humans. Upon seeing a large explosion several miles away, a cow would likely blink, lower its head, and continue to munch grass. The explosion would not immediately affect the cow's practical agenda, which is to eat.
Most humans, and perhaps some higher mammals, would be curious as to the nature, cause, and ultimate ramifications of the explosion. Most of us would like to investigate it. Perhaps the explosion is related to other, smaller explosions. Perhaps it will support or refute a particular model of how things behave. Perhaps the rapidly expanding cloud of gases is pretty and emotionally evocative. In any case, we are fundamentally curious beings.
Does that take into account the expansion of the universe? Is it 400 million light years away now or is that how far away it was when the exposion occurred (presumably it was closer 400 million years ago?)
Well, unfortunately, it's neither. "400 million light years" is close enough so that we can get away with this kind of approximation, but astronomers really don't talk about "distance" at scales much larger than this because it doesn't have much meaning. The "400 million" number was probably derived from a direct measurement of cosmological redshift of the spectra of the explosion. This redshift number just tells us the percentage expansion (well, when you multiply it by 100) of the universe since the emission of the radiation. That's it.
For close objects, the redshift is *approximately* z=(H)(light travel time), but this is increasingly less accurate for redshifts of greater than, say, 0.1. This redshift is about 0.03, so between the emission and reception time, the universe has expanded only about 3%. There's not too much error, then, in saying that it *is* 400 million light years away, if you can live with that kind of error.
The problem is that the "lookback time" and recession velocities depend on what kind of universe we live in --- *how* it has expanded in the meantime. For distances this small it doesn't really matter, but this is why you really never hear *real* astronomers talk about distances to galaxies "10 billion light-years away". It doesn't make any sense, and it's misleading.
... I whiled away many work hours playing Age of Empires II on a local LAN at my programming job. Great for 30 minute breaks, and lots of fun to generate "WTF" responses amongst ourselves with unorthodox strategies.
For coin-op, I was a Robotron fiend. I've really never been so mentally exhausted as when I would play for 8+ hours on one quarter at the local pizza joint in 8th grade. That game was an amazing experience.
I had an Atari ST in college, and my roomies and I would play Sentinel and Gauntlet II endlessly. Wish someone would put out a Sentinel clone again --- great original game.
Maybe my all-time favorite was Doom II. Great, immersive maps, and (like Doom I) you could get the monsters to fight each other. One of the greatest touches to a shoot-em-up I knew of. Great fun to see if I could make it from Level 1 past Level 30 with no 'cheats' (but lots of savegames). I liked charging into some ridiculously populated room with very limited ammo, hiding in a corner and getting off a couple of strategic shots, and watching them turn on each other.
I suppose that, just like all toilets swirl the other direction down under, when the poles swap these computers will run backwards... (hmmm, what would all that pr0n look like in reverse?)
If you check the equations, you'll find that light from a star causes its gravitational field to fall off as 1/r, whereas its mass causes it to fall off as 1/r^2. This is an old equation, originally derived for the gravitational field of a candle.
It's difficult to understand what you're saying, but the gravitational field due to pure radiation does *not* fall of as 1/r. It is stronger that that produced by the equivalent mass density, but only by a factor of 2. It falls off as 1/r^2 just like the field generated from matter.
I personally, have a complete dislike for the idea of dark matter. It seems like a stab in the dark, that missed, and was declared right anyway. "Wow, galaxies spin way faster than we think they should. It's almost like there are invisible halos of super heavy matter surrounding all galaxies." Oh, yeah, beyond being completely invisible Dark Matter exists in halos around galaxies. They are really really heavy but the stars don't fall into the halos or the halos into the stars. It's all magically perfect.
I'm confused as to what really bothers you. Why should the stars "fall" into the halos? Are you implying that there should be a gravitational interaction between the stars and halo? There is --- the anomalously fast rotation rates are precisely the action of the stars "falling" into the halo. And it's inaccurate to describe dark matter as "invisible", at least as much as describing planets orbiting other stars as "invisible". Dark matter is not luminous, so it's hard to detect from some distance away even if the matter itself is opaque to visible light. In fact, one of the more significant searches for candidates of dark matter involved looking for microlensing and microoccultation events --- dark objects passing in front of background stars.
And your sarcasm and supercilious attitude ought to be tempered by the fact that many objects have been theoretically postulated and later discovered based upon anomalous orbital motion. Neptune leaps immediately to mind.
Slashdot Mirror
I like cereal! ---Cheese
It was a Danny Dunn book, "Danny Dunn, Invisible Boy", I *think*. I loved this series when I was a boy.
Lots more than that --- just a quick search of The Sloan Digital Sky Survey yields over 15,000. Probably even a lot more than that are known.
But we're not talking about a duration of radiation in a certain area, but integrating the total number of encounters. If you hang your head outside of a car and open your mouth, you'll swallow twice as many gnats going at 60 mph than you would at 30 mph (if the gnat density is constant in space).
I don't think this is right. First of all, cosmic rays are particles, not radiation (as I think you are implying). But to the point, you would expect to collide with more cosmic rays since you are sweeping out a greater volume due to your velocity. Given some cosmic ray density in space (number of particles per m^3), the greater the volume swept out, the more encounters there will be. Each encounter would still feature relative velocities less than c.
Thousands. Thousands of years ago. HTH.
As an example, in my previous job for a weather company, we'd generate large images of geographic data for a certain area of interest, and separately generate radar or satellite or lightning maps over the same area. We'd then use ImageMagick to combine all the separate images together, along with further generated warning areas, icons, and forecasts representing weather phenomena of interest (tornadoes, mesocyclones, hurricanes) and usually some sort of written annotation (time of image, source). ImageMagick was/is really useful.
Ok, I haven't been keeping up --- this Japanese machine is, I gather, massively parallel. Suppose I wanted to find out which single processor was the speed king for floating point calculations. Is it as simple as sorting for the highest number on SpecFP2000?
Yep, you're right, steveha. I didn't see the second set of quotes --- sorry for attributing that to you. Thanks for pointing that out.
Yeah, it's too bad the focus of the submitter was on the Intelligent Design snippet --- probably the least interesting bit in the article. The most fascinating stuff to a non-specialist like me was the complexity in the genetic code. Much more complex, I gather, than other members of the virus family so far discovered, and in fact sharing some genetic coding with "higher" animals? Wow --- that kind of thing really illusrates what makes science so fascinating.
Well, there's little room for *wild* speculation, as any speculation as to the physical causes of redshift must correspond to mountains of previous data and theory on the topic. Speculate all you want, just be prepared for others more acquainted with the science to tell you where you're off track. And I have no idea where you get the notion that I "pooh-pooh" redshift. It was observed with a value of 3.3%. What's the disagreement? Redshift *is* an effect, not a cause. I just don't follow you.
Clearly you know everything there is to possibly know about astronomy.
Now that's just snarky. You're better than that.
I don't have your email, but if you're still interested, here is the link to the initial observational announcement with the 3.3% reshift cited from the observations: Announcement
and here's a link to the Astronomy Picture of the Day with photos of the relevant portion of the sky, as well as many related links:
APOD discussion
Well, I mean that cosmology and the phenomenon of redshift is, in general, fascinating. So much so that I decided to make it my vocation. In this case, redshift is not much of a factor in the original story, as opposed to your original statements. Who's fighting? I was just trying, unsuccessfully, to point out a common misunderstanding. Carry on with your views if you take such offense at dissent.
Use of the word "terribly" leads me to believe that you're talking down your nose more than you're trying to hold a productive discussion. If that was your intent then, by all means, carry on.
"Terribly," a colloquialism meant to indicate interest to a high degree. I have a hard time imagining things much more deeply interesting than cosmology.
I think it's buried in the original press release or preprint. Anyway, the standard method we use to determine distances like 440 million ly is the Hubble Law --- observe the redshift and then ham-handedly use the classical Doppler formula z=v/c to get the recessional velocity. If the Hubble constant is, say, 50 km/s/Mpc, then we can get the distance of the object. This works ok for reshifts less than 0.1 or so. Working this out for 440 million ly gives a reshift of about 0.03, similar to other galaxies at that distance (like those in the Coma cluster).
You keep saying that the page I linked to is a common misconception but you offer what to back that up? Since this morning I've looked over at least a dozen pages, all of them physics .edu or space related .gov research (No, I wasn't about to look at answers.com or about.com for a scientific discussion) and all of them, if they include mathematical derivations, use the same equations. So what exactly is this common misunderstanding?
I would recommend a scientific discussion. The misunderstanding is in ascribing the redshifts of distant galaxies to an actual recessional velocity through space. If this were the case, then one could use the classical or relativistic Doppler formulas, like the ones to which you linked. But galaxies can be thought of as basically pinned in an expanding space that carries them along for the ride, like points on an expanding rubber band. The points don't move relative to their local position on the rubber band, but as the band stretches they are carried apart from each other.
What exactly am I wrong about? That the redshift phenomena is something interesting to think about? Do you hold some intellectual astroturf on someone else thinking about the effect of redshift? I see in one of your other posts that you assert that you're an astronomy educator. Perhaps you could contribute something educational rather than repeating,"No! You're wrong! I know all about it but I'm not going to describe it at all. Quit thinking about it!"
You're too touchy. I have attempted to describe it twice. Think about it all you want. It's terribly interesting. Most of the good introductory books on astronomy have cosmological disclaimers like the above, some with stronger language than others. The best book for non-specialists about cosmology ever written, in my opinion, is Harrison's "Cosmology: The Science of the Universe". Sometimes it's available via Amazon. But for a discussion of this, try Wiki Redshift
Try kicking your dog if you need to assert your superiority. I was looking for a productive discussion and apparently I fished out someone who wanted to fight.
I think you took my comments badly. Of course redshifts exist. The kind of redshifts we ought to be talking about are cosmological --- these are the ones typically used in computing distances to galaxies. My 3% number is simply the cosmological redshift (I think in the original source they claim 3.3%), which indicates an expansion of the universe of 3% since the signal was emitted. Then you offered an argument based upon a link to a page that suffers from a common misunderstanding, which I pointed out.
You are right that redshifts, in general, distort the timing of distant events. But here, since the redshift is only 3%, the event (locally, at emission) happened only 3% faster. It's not much of a factor, as I was trying to say. If having a "productive discussion" means that I shouldn't point out where you're wrong, then I'll butt out.
They are related to a different class of physical phenomenon.
Cosmological redshift is an indicator of how much the universe has expanded since the radiation was emitted. A redshift of 3% (in this case) means that the universe is now 3% bigger than it was when the light was emitted. In fact, that's *all* the redshift means. Cosmological redshift is completely different from the Doppler shift used, as you say, for motions of stars in our own galaxy.
According to this page a red shift of z=4.25, a recession speed of 0.93c, corresponds to a distance of 12-15 million light years. Nine years ago when I was studying nuclear physics I could probably have told you more distinctly what that means. Assuming it's the velocity remaining, a 7% decrease equates to 12-15 million light years. Assuming a linear relationship (unlikely, but I'm doing the math in my head) then light traveling 440 million light years would experience a decrease of around 250%. That means the gamma rays, by the time they reached Earth, are 2.5 times lower in energy than from the originating point. That's not an order of magnitude but it's definitely significant.
Unfortunately, the linked page is in error. It is a common misunderstanding. Astronomers rarely speak of a "distance" of 12-15 billion light years, because such a distance has no meaning. Is it 12-15 billion ly from the time of emission or reception? And applying special relativistic Doppler shifts is in error since the expansion is for co-moving objects carried along by the expansion of *space*. Galaxies are not rushing through space away from us, but are fairly fixed in an expanding space. It is a subtle, but crucial, difference. The *only* information accurately obtained via cosmological redshifts is the expansion factor. Calculating a lookback time or distance (emission or reception) to an object requires a certain model of expansion that has occurred in the meantime.
A great many people. And it runs the other way --- radiation gets spread out due to cosmic expansion over a long journey, so we actually see the phenomena in slow motion.
The redshift is only about 3%, so probably not an issue here.
Right, but the result of the initial observation is still not deterministic, so you can't use non-locality to send information. At least according to the Copenhagen (most widely held) interpretation of QM.
Most humans, and perhaps some higher mammals, would be curious as to the nature, cause, and ultimate ramifications of the explosion. Most of us would like to investigate it. Perhaps the explosion is related to other, smaller explosions. Perhaps it will support or refute a particular model of how things behave. Perhaps the rapidly expanding cloud of gases is pretty and emotionally evocative. In any case, we are fundamentally curious beings.
Well, unfortunately, it's neither. "400 million light years" is close enough so that we can get away with this kind of approximation, but astronomers really don't talk about "distance" at scales much larger than this because it doesn't have much meaning. The "400 million" number was probably derived from a direct measurement of cosmological redshift of the spectra of the explosion. This redshift number just tells us the percentage expansion (well, when you multiply it by 100) of the universe since the emission of the radiation. That's it.
For close objects, the redshift is *approximately* z=(H)(light travel time), but this is increasingly less accurate for redshifts of greater than, say, 0.1. This redshift is about 0.03, so between the emission and reception time, the universe has expanded only about 3%. There's not too much error, then, in saying that it *is* 400 million light years away, if you can live with that kind of error.
The problem is that the "lookback time" and recession velocities depend on what kind of universe we live in --- *how* it has expanded in the meantime. For distances this small it doesn't really matter, but this is why you really never hear *real* astronomers talk about distances to galaxies "10 billion light-years away". It doesn't make any sense, and it's misleading.
For coin-op, I was a Robotron fiend. I've really never been so mentally exhausted as when I would play for 8+ hours on one quarter at the local pizza joint in 8th grade. That game was an amazing experience.
I had an Atari ST in college, and my roomies and I would play Sentinel and Gauntlet II endlessly. Wish someone would put out a Sentinel clone again --- great original game.
Maybe my all-time favorite was Doom II. Great, immersive maps, and (like Doom I) you could get the monsters to fight each other. One of the greatest touches to a shoot-em-up I knew of. Great fun to see if I could make it from Level 1 past Level 30 with no 'cheats' (but lots of savegames). I liked charging into some ridiculously populated room with very limited ammo, hiding in a corner and getting off a couple of strategic shots, and watching them turn on each other.
Russian
It's difficult to understand what you're saying, but the gravitational field due to pure radiation does *not* fall of as 1/r. It is stronger that that produced by the equivalent mass density, but only by a factor of 2. It falls off as 1/r^2 just like the field generated from matter.
I'm confused as to what really bothers you. Why should the stars "fall" into the halos? Are you implying that there should be a gravitational interaction between the stars and halo? There is --- the anomalously fast rotation rates are precisely the action of the stars "falling" into the halo. And it's inaccurate to describe dark matter as "invisible", at least as much as describing planets orbiting other stars as "invisible". Dark matter is not luminous, so it's hard to detect from some distance away even if the matter itself is opaque to visible light. In fact, one of the more significant searches for candidates of dark matter involved looking for microlensing and microoccultation events --- dark objects passing in front of background stars.
And your sarcasm and supercilious attitude ought to be tempered by the fact that many objects have been theoretically postulated and later discovered based upon anomalous orbital motion. Neptune leaps immediately to mind.