> If you assume that we are a stationary object and also assuming that space is flat.
No, if you assume that we are a stationary object and that space is flat, then an object with a redshift of 6.3 would mean that it is moving away at 6.3 * speed of light = 70 million miles a minute. The 21 million miles a minute takes into account the curvature etc.
For anyone interested, here's the email that I received from the author:
Hi John,
Thanks for your message. I was the principle author of the press release, so I will try to answer your question. I should note that the press release was reviewed by numerous scientists. But it was edited at NASA headquarters before it was made public.
In my original draft, I purposefully avoided making the statement that the GRB was 7.5 billion light-years from Earth, because as your message implies, it is problematic to express specific distances when one is talking about events that happened in the very distant past, because the universe is rapidly expanding. Such is the case when trying to express a "distance" to GRB 080319B.
The most relevant direct "distance" measurement is the object's redshift, which was measured to be 0.94. As the press release explained, this measurement tells astronomers how much the GRB's light was "stretched" by cosmic expansion. I used this popular website from a renowned UCLA cosmologist to convert the object's redshift to a light-travel time:
When I entered the redshift and the cosmological parameters based on the latest results from the WMAP satellite and large-scale galaxy surveys, the calculator gave me a light-travel time of 7.5 billion years. In other words, the light from this GRB was emitted 7.5 billion years ago. But at the time the burst occurred, Earth didn't even exist, so how does one express a "distance" between one object and another object that does not exist? In addition, 7.5 billion years ago, the visible universe was a much smaller place than it is now, because cosmic expansion has made the universe much bigger during those intervening 7.5 billion years. The GRB's host galaxy and the Milky Way Galaxy would have been much closer back then than they are today (please note that the Milky Way would have been a lot different back then, but it undoubtedly existed at that time). In fact, back then, the two galaxies would have been much closer than 7.5 billion light-years. And yet because of cosmic expansion, the two galaxies are currently much farther apart than 7.5 billion light-years. So there really is not an ideal way to express such a huge distance.
In my opinion, the best way to express such a huge distance in a rapidly expanding universe at the level of a popular audience is to express distances in terms of light-travel time, which is what I did in the original draft of the press release. And because our best current measurements suggest that the universe is 13.7 billion years old, an event taking place 7.5 billion years ago is roughly halfway across the visible universe. Some of the scientists at NASA probably felt that it was important to specify a distance in a unit of distance rather than in a unit of time, so they translated the light travel time to a distance in light-years. I realize this is imprecise from a strict scientific perspective, but the NASA scientists concluded that there is no better way to express it, and I cannot think of a better way to do it.
The problem, of course, is that the most precise way to express the distance is to state the redshift, which I did in the press release. Unfortunately, the term "redshift" has little meaning to the media and public, and the general public does not have the familiarity with astronomical terminology to be able to translate a redshift of 0.94 into a distance that has any deep meaning.
I emailed the author, and they have now corrected the article.
The article now just says:
The explosion was so far away that it took its light 7,500,000,000 (7.5 billion) years to reach Earth! In fact, the explosion took place so long ago that Earth had not yet come into existence.
And the title has also been changed to "A Stellar Explosion You Could See on Earth!" (Instead it was something about that it happened half way across the universe from us)
(Just for reference, I am doing an MSc in this field.)
Your definition would be what cosmologists call 'comoving distance'. I have never seen a light year defined in this way however. The rate of expansion changes with time, so under your definition you would end up with things like that 2 * 1 light year != 2 light years, etc.
It also means that a light year now, would be a different distance (in km) than a light year was a year ago, etc.
> As fast as it can go, the speed of light you know, twelve-million miles a minute and that's the fastest speed there is.
That's actually quite wrong. We can see stars with a redshift of 6.3, meaning that it is moving away from us at 21 million miles a minute (compared to the 12 million miles a minute for the speed of light).
Well, different sources say different things, so I took the lower bound. (For example http://en.wikipedia.org/wiki/Observable_universe states 78billion light years across for a lower bound based on WMAP data) And then I halved it for the radius, and rounded. The exact number doesn't matter for my explanation.
> Later that evening, the Very Large Telescope in Chile and the Hobby-Eberly Telescope in Texas measured the burst's redshift at 0.94. A redshift is a measure of the distance to an object. A redshift of 0.94 translates into a distance of 7.5 billion light years, meaning the explosion took place 7.5 billion years ago, a time when the universe was less than half its current age and Earth had yet to form. This is more than halfway across the visible universe
This contains some serious misunderstandings. Just because it's at a distance of 7.5 billion light years away, that doesn't mean it happened 7.5 billion years ago because the universe has expanded since then. We have seen objects that are more than 50 billion light years away, but the universe is only 13 billion years old.
Also this object is nowhere near 'halfway across the visible universe'. The visible universe is 46 billion light years in radius (with us at the centre).
I use vmware which works great if you have 2GB of memory or so. (You can run it on a lot less, but I find 2GB is enough to mean that I don't have to worry about it running, and can just leave it always on)
And it's people like you that are the real cause of this problem. Anyone that complains at all about the way that the FBI are going about this, is immediately labelled a child molester by people like you.
There are plenty of cases in the news where people have had their equipment seized and then never returned, despite no charges ever brought against them.
>So, you're saying it's possible that everything we see right now was somehow crammed together in the last 6000 years within a 6000 light-year radius, and then expanded at some break-neck speed to 93 billion light years across
Yes. It wouldn't violate any known physical laws that I can think of, in terms of just the expansion etc
> without ripping things to shreds?
I agree - And you couldn't really get the stars/planets etc to form.
> Of course, that example assumes Earth stood still for 6000 years collecting that light. Which still makes your hypothesis impossible in several ways...
Why would it not stand 'still'? Where would it go?
> Or were you joking? You know, your joke up here, my head down here, big whoosh? I'm just simply pointing that you can have objects which are further away than the age of the universe.
> (after I'd pointed out that we could easily find objects in the sky well over 6k light years away, and if they were in fact several million/billion light years away, how could the light be reaching us if the universe were only 6k years old?).
Actually this could be possible if the universe expanded very rapidly. In fact the universe is 13.73 million years old, but 93 billion light years across.
I think the trouble is that the vast majority of people don't specify, and that it is opt-in by default. Personally I think it should be opt-out by default - that would solve the problem.
It is proven (Bell's inequality) that either one of the following two statements is false:
1. Objects have a definite state 2. The effect of changing something can't travel faster than the speed of light.
Quantum entanglement does show that the particles communicate faster than the speed of light (and thus have no regard for causality). However the catch is that information can't travel faster than speed of light. Information meaning information that we, as big classical beings, have access to. We are prevented from accessing this quantum information. We can't communicate to someone else faster than the speed of light. So causality in the 'big' classical world is never broken.
> This is true but I think not for the reasons you believe. Basic quantum crypto provides confidentiality only. To keep from being hacked, you must provide authentication as well (Alice must be able to prove she is communicating with Bob and not Eve)
I am a theoretical particle physicist, and I understand what you are trying to say, and I understand what the replies are saying as well.
You are correct that the 'basic' quantum cryptography that is taught can be hacked. This is just because a simplified version is used in books, because it's confusing enough.
Others who point out the no cloning principle are exactly right. You cannot read and then reemit a photon with the same polarization (for example). Basically the way it work is like this:
Alice picks one of four polarizations at random, out of vertically polarised (0 degrees, say), horizontally polarised 90 degrees), or polarised at 45 degrees, or at -45 degrees.
Bob then picks, at random, whether to measure the polarization horizontally/vertically or to rotate his polariser 45 degrees and measure at 45 degrees or at -45 degrees.
If Bob chooses the 'wrong' direction, he'll get a random result. If he chooses the 'right' direction, then he'll get the correct result. After this is done, Alice tells Bob how she sent it, and Bob can discard all the measurements in which he chose the wrong direction to measure in. If Bob tells Alice the same results that Alice sent, then they know there was no interference.
There is no way to measure the 'true' polarization of the light that Alice sent, because you have to have your polariser either measuring horizontal/vertical, or measuring at 45/-45. You can't have it do both. So noone can monitor and then reemit a photon with the same polarization.
> Obviously, its the authors work, but the journals do a ton of work.
But don't we pay for that work to be done when we submit the article, and then pay again to buy the journal? Doesn't that alone cover over the cost of editing it? (A genuine question - I can imagine that it does not).
Slashdot Mirror
> If you assume that we are a stationary object and also assuming that space is flat.
No, if you assume that we are a stationary object and that space is flat, then an object with a redshift of 6.3 would mean that it is moving away at 6.3 * speed of light = 70 million miles a minute. The 21 million miles a minute takes into account the curvature etc.
For anyone interested, here's the email that I received from the author:
Hi John,
Thanks for your message. I was the principle author of the press release, so I will try to answer your question. I should note that the press release was reviewed by numerous scientists. But it was edited at NASA headquarters before it was made public.
In my original draft, I purposefully avoided making the statement that the GRB was 7.5 billion light-years from Earth, because as your message implies, it is problematic to express specific distances when one is talking about events that happened in the very distant past, because the universe is rapidly expanding. Such is the case when trying to express a "distance" to GRB 080319B.
The most relevant direct "distance" measurement is the object's redshift, which was measured to be 0.94. As the press release explained, this measurement tells astronomers how much the GRB's light was "stretched" by cosmic expansion. I used this popular website from a renowned UCLA cosmologist to convert the object's redshift to a light-travel time:
http://www.astro.ucla.edu/~wright/CosmoCalc.html
When I entered the redshift and the cosmological parameters based on the latest results from the WMAP satellite and large-scale galaxy surveys, the calculator gave me a light-travel time of 7.5 billion years. In other words, the light from this GRB was emitted 7.5 billion years ago.
But at the time the burst occurred, Earth didn't even exist, so how does one express a "distance" between one object and another object that does not exist? In addition, 7.5 billion years ago, the visible universe was a much smaller place than it is now, because cosmic expansion has made the universe much bigger during those intervening 7.5 billion years. The GRB's host galaxy and the Milky Way Galaxy would have been much closer back then than they are today (please note that the Milky Way would have been a lot different back then, but it undoubtedly existed at that time). In fact, back then, the two galaxies would have been much closer than 7.5 billion light-years. And yet because of cosmic expansion, the two galaxies are currently much farther apart than 7.5 billion light-years. So there really is not an ideal way to express such a huge distance.
In my opinion, the best way to express such a huge distance in a rapidly expanding universe at the level of a popular audience is to express distances in terms of light-travel time, which is what I did in the original draft of the press release. And because our best current measurements suggest that the universe is 13.7 billion years old, an event taking place 7.5 billion years ago is roughly halfway across the visible universe. Some of the scientists at NASA probably felt that it was important to specify a distance in a unit of distance rather than in a unit of time, so they translated the light travel time to a distance in light-years. I realize this is imprecise from a strict scientific perspective, but the NASA scientists concluded that there is no better way to express it, and I cannot think of a better way to do it.
The problem, of course, is that the most precise way to express the distance is to state the redshift, which I did in the press release. Unfortunately, the term "redshift" has little meaning to the media and public, and the general public does not have the familiarity with astronomical terminology to be able to translate a redshift of 0.94 into a distance that has any deep meaning.
Best regards,
Robert Naeye, NASA Goddard Space Flight Center
Update:
I emailed the author, and they have now corrected the article.
The article now just says:
The explosion was so far away that it took its light 7,500,000,000 (7.5 billion) years to reach Earth! In fact, the explosion took place so long ago that Earth had not yet come into existence.
And the title has also been changed to "A Stellar Explosion You Could See on Earth!" (Instead it was something about that it happened half way across the universe from us)
(Just for reference, I am doing an MSc in this field.)
Your definition would be what cosmologists call 'comoving distance'. I have never seen a light year defined in this way however. The rate of expansion changes with time, so under your definition you would end up with things like that 2 * 1 light year != 2 light years, etc.
It also means that a light year now, would be a different distance (in km) than a light year was a year ago, etc.
At the risk of being spoil-sport:
> As fast as it can go, the speed of light you know, twelve-million miles a minute and that's the fastest speed there is.
That's actually quite wrong. We can see stars with a redshift of 6.3, meaning that it is moving away from us at 21 million miles a minute (compared to the 12 million miles a minute for the speed of light).
Well, different sources say different things, so I took the lower bound. (For example http://en.wikipedia.org/wiki/Observable_universe states 78billion light years across for a lower bound based on WMAP data) And then I halved it for the radius, and rounded. The exact number doesn't matter for my explanation.
From the article:
> Later that evening, the Very Large Telescope in Chile and the Hobby-Eberly Telescope in Texas measured the burst's redshift at 0.94. A redshift is a measure of the distance to an object. A redshift of 0.94 translates into a distance of 7.5 billion light years, meaning the explosion took place 7.5 billion years ago, a time when the universe was less than half its current age and Earth had yet to form. This is more than halfway across the visible universe
This contains some serious misunderstandings. Just because it's at a distance of 7.5 billion light years away, that doesn't mean it happened 7.5 billion years ago because the universe has expanded since then. We have seen objects that are more than 50 billion light years away, but the universe is only 13 billion years old.
Also this object is nowhere near 'halfway across the visible universe'. The visible universe is 46 billion light years in radius (with us at the centre).
I use vmware which works great if you have 2GB of memory or so. (You can run it on a lot less, but I find 2GB is enough to mean that I don't have to worry about it running, and can just leave it always on)
Heh, I've downloaded a movie that I have on DVD, since that was easier and almost just as fast as just ripping it myself.
And it's people like you that are the real cause of this problem. Anyone that complains at all about the way that the FBI are going about this, is immediately labelled a child molester by people like you.
There are plenty of cases in the news where people have had their equipment seized and then never returned, despite no charges ever brought against them.
How long until people start pasting this FBI-honeypot link to trick people into clicking it..
Oh, okay, that makes a lot of sense. (I don't know much about health insurance - we don't really have to get it in the UK)
What if you get a serious illness?
Yeah, stupid typo. The point is just that it's larger than its age.
Heh, right billion not million sorry.
>So, you're saying it's possible that everything we see right now was somehow crammed together in the last 6000 years within a 6000 light-year radius, and then expanded at some break-neck speed to 93 billion light years across
Yes. It wouldn't violate any known physical laws that I can think of, in terms of just the expansion etc
> without ripping things to shreds?
I agree - And you couldn't really get the stars/planets etc to form.
> Of course, that example assumes Earth stood still for 6000 years collecting that light. Which still makes your hypothesis impossible in several ways...
Why would it not stand 'still'? Where would it go?
> Or were you joking? You know, your joke up here, my head down here, big whoosh?
I'm just simply pointing that you can have objects which are further away than the age of the universe.
> (after I'd pointed out that we could easily find objects in the sky well over 6k light years away, and if they were in fact several million/billion light years away, how could the light be reaching us if the universe were only 6k years old?).
Actually this could be possible if the universe expanded very rapidly. In fact the universe is 13.73 million years old, but 93 billion light years across.
I think the trouble is that the vast majority of people don't specify, and that it is opt-in by default. Personally I think it should be opt-out by default - that would solve the problem.
Well a lot of scientists do end up lecturing some of the week. And there's barely enough to time to do that.
It is proven (Bell's inequality) that either one of the following two statements is false:
1. Objects have a definite state
2. The effect of changing something can't travel faster than the speed of light.
Quantum entanglement does show that the particles communicate faster than the speed of light (and thus have no regard for causality). However the catch is that information can't travel faster than speed of light. Information meaning information that we, as big classical beings, have access to. We are prevented from accessing this quantum information. We can't communicate to someone else faster than the speed of light. So causality in the 'big' classical world is never broken.
> Hmm. I think you meant you cannot read and reemit with 100% fidelity. http://www.icfo.es/images/publications/J05-055.pdf
I did not know about this - very interesting.
> This is true but I think not for the reasons you believe. Basic quantum crypto provides confidentiality only. To keep from being hacked, you must provide authentication as well (Alice must be able to prove she is communicating with Bob and not Eve)
That is the reason that I was thinking of.
On second thoughts, if you had a wide enough 'beam' with this one photon in it, it should work okay.
Well, a single photon can't have a direction. So it doesn't do much bouncing.
Hi,
I am a theoretical particle physicist, and I understand what you are trying to say, and I understand what the replies are saying as well.
You are correct that the 'basic' quantum cryptography that is taught can be hacked. This is just because a simplified version is used in books, because it's confusing enough.
Others who point out the no cloning principle are exactly right. You cannot read and then reemit a photon with the same polarization (for example). Basically the way it work is like this:
Alice picks one of four polarizations at random, out of vertically polarised (0 degrees, say), horizontally polarised 90 degrees), or polarised at 45 degrees, or at -45 degrees.
Bob then picks, at random, whether to measure the polarization horizontally/vertically or to rotate his polariser 45 degrees and measure at 45 degrees or at -45 degrees.
If Bob chooses the 'wrong' direction, he'll get a random result. If he chooses the 'right' direction, then he'll get the correct result. After this is done, Alice tells Bob how she sent it, and Bob can discard all the measurements in which he chose the wrong direction to measure in. If Bob tells Alice the same results that Alice sent, then they know there was no interference.
There is no way to measure the 'true' polarization of the light that Alice sent, because you have to have your polariser either measuring horizontal/vertical, or measuring at 45/-45. You can't have it do both. So noone can monitor and then reemit a photon with the same polarization.
> Obviously, its the authors work, but the journals do a ton of work.
But don't we pay for that work to be done when we submit the article, and then pay again to buy the journal? Doesn't that alone cover over the cost of editing it? (A genuine question - I can imagine that it does not).