pageok
pageok
pageok
Talk About Old News:
From the Associated Press:
STAR EXPLODES HALFWAY ACROSS UNIVERSE
  The explosion of a star halfway across the universe was so huge it set a record for the most distant object that could be seen on Earth by the naked eye.
  A star 7.5 billion light years away exploded, giving off the brightest gamma-ray burst afterglow ever seen.
  The aging star, in a previously unknown galaxy, exploded in a gamma ray burst 7.5 billion light years away, its light finally reaching Earth early Wednesday.
  The gamma rays were detected by NASA's Swift satellite at 2:12 a.m. "We'd never seen one before so bright and at such a distance," NASA's Neil Gehrels said.
This story is sooooo 7.5 billion years ago.
The McGehee (mail) (www):
And nobody thought to report on it until now!? No wonder nobody trusts the media.
3.22.2008 1:51pm
Elliot Reed (mail):
Sorry to be redundant, but this is par for the course for the treasonous liberal media.
3.22.2008 2:26pm
CEB:
Or maybe it just happened and people on Earth won't find out about it for another 7.5 billion years...

If anyone is in the mood for a discussion of the metaphysics of this, here goes: We tend to think of time as having a past, present, and future. The past is determined (cannot be altered or undone), the future is undetermined (different possible futures may occur based on our choices, random events, etc.), and the present is where the two meet. The problem comes with trying to figure out when "now" is. I snap my fingers and say "now." A person across the room perceives that a few milliseconds or after me. So "now" is different for me and the observer. If there can be no real border between the past and the future, either the past is still indetermined or the future is already determined.
3.22.2008 2:41pm
OrinKerr:
CEB,

I don't see the metaphysical difficulty here. If I send a postal letter to you on Tuesday and it arrives on Wednesday, the "moment of the letter" is Tuesday for me and Wednesday for you. It doesn't mean there is no border between the past and the future, or that the past is indetermined or the future determined. It just means that it took a day for the thing I experienced to reach you and become the thing you experienced. Or so it seems to me; maybe I'm missing something.
3.22.2008 2:57pm
liberty (mail) (www):
CEB: You snapped your fingers "now", they perceived it a few milliseconds after- that causes no paradox unless perception is reality, which is a big assumption.
3.22.2008 2:58pm
John Burgess (mail) (www):
Yes, Bishop George Berkeley ran that one up the flagpole in 1710 or so, when he philosophized about that 'perception is reality' business.

Nothing new here (except relative to that 7.5 billion-year-old starburst).
3.22.2008 3:09pm
John Armstrong (mail) (www):
Orin, CEB is oversimplifying, but you are, indeed, missing something. However, it's not a something that affects your interpretation of the posted story.
3.22.2008 3:15pm
Jerry F:
Isn't it sort of a weird coincidence that the star would have exploded precisely 7.5 billion years ago so that we would see it now (as opposed to exploding any time over the 1,000,000,000 years before the 20th century, in which case we presumably would never have been able to see it)?
3.22.2008 3:23pm
OrinKerr:
John Armstrong,

Thanks for the response. Can you clue me in as to what I am missing? I enjoy learning, and if you can teach me, I would appreciate it.
3.22.2008 3:30pm
Smokey:
In The Fabric Of The Cosmos, Harvard physicist Brian Greene explains that the past, in addition to the future, has infinite possibilities. Like the future, the past can change, too. Therefore, "now" is an artifact.

One of the passages in Greene's interesting book explains the concept of inflation [the expansion of the universe following the Big Bang, not monetary inflation].

The observable universe is ~13.8 billion years old, which only means that our "event horizon" has that limit; the actual universe is bigger. Much bigger.

Prof. Greene explains physicists' [very conservative] calculation of the universe's expansion during inflation this way: if our observable universe were the size of a grain of sand, the actual size of the universe is roughly comparable to the size of the earth.

The reason we can't see it all is because of Hubble's red shift, where the more distant an object is, the more that light is shifted toward a lower frequency. At the limit of the observable universe, the frequency of light becomes essentially zero. So we're in the middle of a bubble, the size of which is set by the red shift.

Interestingly, an observer 7 1/2 billion light years away is also in the center of their own bubble - shared with us - just as we are in the center of our bubble. The frame of reference is always the observer.

Anyway, that's Greene's [almost math-free] explanation of reality. For his reasoning of how the past isn't set in stone any more than the future is, check out the book. It's too much heavy slogging to go into here.
3.22.2008 3:36pm
Bill Poser (mail) (www):
It may not be news, but at least its fit to print.
3.22.2008 3:37pm
Doc W (mail):
Well, in relativity, each point in spacetime has its own absolute future and past, defined by the so-called "light cone." All points ("events") that could affect us here and now via light waves or material particles constitute our past. All point that we could affect the same way constitute our future. The rest of spacetime is "elsewhere." Since I'm writing this at a different point in spacetime than any of you folks fortunate enough to be reading it, our futures, pasts, and elsewheres differ, although they overlap.
3.22.2008 3:42pm
Fub:
OrinKerr wrote at 3.22.2008 1:57pm:
I don't see the metaphysical difficulty here. If I send a postal letter to you on Tuesday and it arrives on Wednesday, the "moment of the letter" is Tuesday for me and Wednesday for you.
I think we can all agree that blowing up entire galaxies is an inherently dangerous activity, and that warning of the demolition arrived entirely too late. But I'm not sure I understand the applicable law.

Can you recommend a good treatise on strict liability, space-time hyperbolic orthogonality and the mailbox rule?
3.22.2008 4:00pm
CEB:
I'm in way over my head here and I realize I probably don't even know enough to raise coherent questions on this subject, but it seems that our intuitive notion that there is a "present," a nexus at which things go from undetermined to determined, is only in our limited perception. For example (and again, this might be an incoherent example, but here goes): in a few moment I will toss a coin. At this point it could be heads or tails. [...] Just tossed it; it's tails, and cannot become heads. When and how did the possibility of heads cease to exist?
3.22.2008 4:01pm
Gaius Marius:
If in the distant future, our descendents are able to travel faster than the speed of light, then they will be able to travel from the future to our present time and observe us first hand.
3.22.2008 4:25pm
Bill Poser (mail) (www):

Can you recommend a good treatise on strict liability, space-time hyperbolic orthogonality and the mailbox rule?


A topic such as this cries out for economic analysis. Surely Judge Posner has written on it. :)
3.22.2008 4:26pm
Doc W (mail):
CEB, if I may equate "present" and "simultaneous with now," in relativity there isn't a problem with two events being simultaneous if they happen at the same place. If they happen at different places, then they might or might not be simultaneous defending on the frame of reference of the observer. To the extent that the coin flip follows classical (non-quantum) physics, I don't think there's a problem. But possibilities becoming actualities is real interesting in quantum physics. There's an old book by Nick Herbert called Quantum Reality that I always liked--it's 20 years old but still pretty good and available on Amazon for few bucks.
3.22.2008 4:53pm
Paul Milligan (mail) (www):
It may be old news, but that's no reason to make light of it.
3.22.2008 4:55pm
John Armstrong (mail) (www):
Doc W is getting there.

Basically, our intuition says there's a three-dimensional "space" that things move around in as a one-dimensional "time" passes. Together, they make up a four-dimensional "spacetime". We call the points of this combination, "events".

Think of it like a flipbook, where a bunch of two-dimensional pictures are stacked up into a three-dimensional stack, and then viewed in sequence. We think of each page in the book as a moment -- a "now". An object sitting still traces a vertical line through the book (since it stays in the same place), while a moving one traces a diagonal line.

So here's your letter example in this picture: I send you a letter at event A in spacetime, and you receive it at event B. The path the letter takes in space gets pulled up into a path in spacetime, which keeps track of when the letter was where. So your interaction with the letter is in one page of the flipbook (one "now") while mine was in an earlier page (a different "now"). All events -- all physics (except some things about quantum mechanics, which I'm ignoring) -- is purely local in spacetime, dealing only with what's happening at this point in spacetime, and not caring what's happening elsewhere.

The problem is this: we're thinking of a 3-D slab sliced up into 2-D pages (or in real life, a 4-D spacetime sliced into 3-D "nows"). But why did we have to choose that way of slicing up space into pages?

When you slice up spacetime, you say events are "simultaneous" if they lie on the same slice. But then I come along and slice it up in a different way; maybe at an angle to your slices. Then I have my own notion of "simultaneous", and it's not going to agree with yours. We can find events you say happen at the same time, but I say happen at different times. This throws off the whole notion of what "now" means. And, amazingly, it turns out that this actually happens.

When I'm staying still, I'm slicing up my flipbook into horizontal pages, which are perpendicular to my vertical "world-line". I see you moving along, tracing out your diagonal world-line. But as far as you're concerned, you're the one standing still. So you make your "now" pages perpendicular to your own line. Your pages don't agree with mine!

The thing is, we don't notice this in practice because the speeds we're used to seeing in the real world are so insanely small that the little difference between your notion of simultaneous and mine never really get that far off. It only makes a difference when you're going some significant fraction of the speed of light.

For instance, there are particles in cosmic rays that we know only last a fraction of a second in our laboratories, but we see them making the journey from the edge of our atmosphere to the surface of the Earth in a few seconds. How can it survive that long? Because to the particle the trip only lasts a fraction of a second. The clock it carries disagrees with ours because it's moving so fast with respect to ours.

So, what's going on out in space? We've got beams of light travelling from the event "star goes boom" to the event "detector in the telescope triggers". We know exactly how fast light moves, and we can figure out how far away the star was. We define the distance in time (how long ago) to be whatever it would take for light to travel that distance, since if we use our method of slicing up spacetime into "nows", that's roughly the page the star went boom on. Now we're back to a situation roughly analogous to your letter, and the same analysis above applies.
3.22.2008 4:58pm
OrinKerr:
John,

Oh, I agree that shared concepts of time become complicated when v/c is no longer extremely close to zero. I didn't think CEB's question raised that scenario, but was rather dealing with more run of the mill experiences where we can treat v/c as essentially zero.
3.22.2008 5:19pm
Richard Nieporent (mail):
Smokey please stick to a subject you know something about. Your explanation was pure nonsense.
3.22.2008 5:26pm
Jim Rhoads (mail):
I blame Bush.
3.22.2008 5:44pm
Smokey:
Richard Nieporent:
Smokey please stick to a subject you know something about. Your explanation was pure nonsense.
What particular part was 'pure nonsense'? I was giving a synopsis of Brian Greene's book. Maybe I didn't explain it well enough. But, "nonsense"?? Where, exactly?
3.22.2008 7:21pm
Richard Nieporent (mail):
What particular part was 'pure nonsense'?

Smokey, how about:

At the limit of the observable universe, the frequency of light becomes essentially zero

or Like the future, the past can change, too.

or The observable universe is ~13.8 billion years old, which only means that our "event horizon" has that limit.
3.22.2008 8:10pm
PersonFromPorlock:
And just to be picky, the headline's wrong. If a star had exploded "halfway across the Universe," it would have been pretty obvious (!). What they meant was "Star Halfway Across the Universe Explodes."
3.22.2008 8:13pm
Bender (mail):
Light cones are the best way to understand the issues involved. Any good introduction to Special Relativity will explain them. The event in question was about (ic)7.5 billion years in the past light cone of "current" earth measured along the time coordinate of the earth's inertial frame. Intuitive concepts of simultaneity apply only when events occur very close to each other in the same inertial frame; and then only approximately.
3.22.2008 8:36pm
Bender (mail):
And it's a good thing this didn't happen on our side of the Milky Way. If it did we'd all be crispy critters.
3.22.2008 8:39pm
Mac (mail):
Well, whatever. Thanks, Orin. It was very neat and I enjoyed the pictures. Kind of puts things into perspective, doesn't it? Or, how to make feel soooo utterly insignificant.

Now then, watching the History channel, I understand if this happens a bit closer to Earth, we are all toast, literally. I think even the roaches.
3.22.2008 8:47pm
Richard Nieporent (mail):
Before it exploded, the star was about 40 times bigger than our sun. The explosion vaporized any planet nearby, Gehrels said.

Ya think?! Are they sure it just wasn't the Vogons making way for a hyperspatial express route?
3.22.2008 9:03pm
Mac (mail):

Now then, watching the History channel, I understand if this happens a bit closer to Earth, we are all toast, literally.


Actually, speaking of the space time continuum thingy, we could already be toast and just not know it.
3.22.2008 9:35pm
Sasha Volokh (mail) (www):
Orin: You're treating the Volokh Conspiracy as essentially zero???
3.22.2008 10:39pm
Smokey:
Richard Nieporent:

Every concept you referred to was taken directly from Prof. Greene's book. Feel free to argue with him if you disagree [but keep in mind that he's got a physics doctorate and was a Rhodes Scholar].

Thinking about these very strange concepts, which are extremely counter-intuitive, caused the same type of consternation for Newtonian classicists a century ago when special and general relativity came on the scene.

The concepts mentioned do not disagree with other posters here. Maybe I wasn't as good at explaining them as others. But that does not make anything I quoted from Prof. Greene "pure nonsense."

Rather than simply dismissing these concepts as nonsense, perhaps you can refute them with your own hypothesis. If it's better than Greene's, there's a Nobel waiting for you. But it's playing a weak hand to simply say, in effect, "Why, that's crazy!"

I suggest reading Greene's books for a better understanding than I can give here. For under ten bucks you can get a lot of knowledge.
3.22.2008 10:41pm
Richard Nieporent (mail):
Smokey, I am not arguing with Professor Greene, I am simply saying that your interpretation of what he said is wrong. For example, the red shift causes the frequency of light to shift to a value that is outside of the visible spectrum. It does not shift it to zero frequency.
3.22.2008 10:55pm
james832:
There are billions of stars, there are billions of galaxies, there are probably billions of univeres, their light just has not gotten here yet.
3.22.2008 11:56pm
Tareeq (www):
Smokey, I haven't read Professor Greene's book (the one you cite anyway) but I suspect you're misreading his work when you say that the past changes. Greene will never win a Nobel. He's a populist, like Sagan (and good for him, we need more) but even so, the so-far unproven theories he populizes are so difficult that it's pretty easy even for a well-educated layman to misread Greene's books.

That said, when Greene builds a TARDIS I hope he invites me along.
3.22.2008 11:58pm
Tareeq (www):
I should have said "so far untested" theories. String theory is still the big dog in town though it's coming under criticism because it isn't "elegant" at all, as Greene described it in his first book.

The good news is that CERN comes online this year or next, and it may be able to help verify some of the predictions of string theory,
3.23.2008 12:09am
Randy R. (mail):
"but I suspect you're misreading his work when you say that the past changes."

You obviously have never met a politician.
3.23.2008 2:00am
Amused:
I am surprised they didn't go to McCain for a comment.
3.23.2008 1:50pm
Smokey:
Smokey, I am not arguing with Professor Greene, I am simply saying that your interpretation of what he said is wrong. For example, the red shift causes the frequency of light to shift to a value that is outside of the visible spectrum. It does not shift it to zero frequency.
Then at what particular frequency does the red shift stop? I'd like to hear your interpretation of that question. Seriously.
3.23.2008 3:13pm
LM (mail):
Smokey,

Your explanation was the only one that made sense to me. If there's any solace in that, then take it, because I assume it indicates nothing good about the chances of what you said being accurate.
3.23.2008 4:07pm
The Real Bill (mail):
Smokey,

The problem is not you, but Greene. What he is writing of is nearly pure speculation, not scientific fact. This is, sadly, the state of modern theoretical physics. (I think string theorists have been spending too much time in the humanities department.)
3.23.2008 4:37pm
Richard Nieporent (mail):
Then at what particular frequency does the red shift stop? I'd like to hear your interpretation of that question. Seriously.

I'm not trying to be snarky but that is a nonsensical question. I take it that you do not have a degree in physics. Unfortunately you are trying to get a simple answer without having an understanding of the physics. That is not easy to do. That is also why reading Greene's book can be confusing.
3.23.2008 5:10pm
Smokey:
LM:
Your explanation was the only one that made sense to me. If there's any solace in that, then take it, because I assume it indicates nothing good about the chances of what you said being accurate.
That backhanded complement made my day! I actually laughed out loud.

I enjoyed Greene's book because it is speculation. But what else do we have when we're discussing the future of physics? It's all speculation; nothing's been proven. That doesn't make it less interesting. And I would rather get my physics speculation from a physics prof than from L. Ron Hubbard or Al Gore.

Thanks to all for the comments. For those still questioning time travel, maybe this guy has the answers.
3.23.2008 9:10pm
The Real Bill (mail):

I enjoyed Greene's book because it is speculation. But what else do we have when we're discussing the future of physics? It's all speculation; nothing's been proven.
Wow! That is NOT how physics is supposed to work.
3.23.2008 11:07pm
Richard Nieporent (mail):
I think this is a fitting final comment for this thread. I just read the mystery novel The Old Wine Shades by Martha Grimes that uses Quantum Mechanics and String Theory as a plot device (yes, really). Two of the characters in the book were discussing a third character, who is a physicist. One of then says is he crazy and the other responded no they just sound that way.
3.23.2008 11:24pm
John Herbison (mail):
I am surprised that no one on this comment thread has posited that the earth is only about 6,000 years old.

Where are the fundamentalists?
3.23.2008 11:37pm
Fub:
Richard Nieporent wrote at 3.23.2008 10:24pm:
I think this is a fitting final comment for this thread.
Well, I'm disappointed. I was hoping that you would enlighten us on an issue for which you took Smokey to task.

In particular:

Assuming special relativity applies, what is the observed wavelength in our reference frame, of a light wave of wavelength L (in the source reference frame) emitted by a source moving directly away from us, in the limit as the source's speed relative to us approaches the speed of light?

Simpleminded hacking through the special relativistic doppler equation sure looked to me like the observed frequency would approach zero (or the observed wavelength approach infinity).

That's another way of saying you can't get here from there in the limit, which is what I thought Smokey referred to as an "event horizon".

But I haven't thought carefully about anything remotely like this stuff for over forty years, so I was hoping you or someone else who knows the subject well would clarify those issues Smokey raised.
3.24.2008 1:25am
Kent G. Budge (mail) (www):
Since I'm a physicist, the philosophy of causality in special relativity is something I'm supposed to know something about.

Bottom line is that the Universe consists of "events", happenings at a certain location at a certain time. Each event has a pair of "light cones" associated with it, one backwards in time, and one forwards in time.

The backwards light cone contains the set of other events that may have influenced the event we're examining. The forward light cone contains the set of events that may be influenced by the event we're examining.

Between the two light cones is the set of events that can have no causal connection with the event we're examining. A supernova seven billion light years away, going off "now", whatever that means, is an event that is causally disconnected from the event of me posting this message.

Turns out the light cones are relativistically invariant. (In fact, they can be used to construct a definition of relativistic invariance.) Causality looks the same to every observer. It's the one really fixed aspect of special relativity.

Light travels precisely on the light cones -- that's why they're called light cones. Nothing travels faster than light, which is why the light cones mark the boundaries of events that might possibly be causally connected.

Don't know if this advances the discussion at all, but who of us can resist showing off his special expertise?
3.24.2008 1:28am
Farmer/Lawyer:
The discussions recorded here are actually quite nicely encapsulated in episode 47 of Star Trek the Next Generation, where Data's evil twin brother Lore lures the crew of the Enterprise to the far side of the universe where they are left with nothing more than a Doll Sheep and a flagon of Scotch whiskey. Picard experiences telepathic communication (through time and space) with prior series chief engineer Scotty, who is briefly seen orbiting the earth in a dis-embodied translucent state. Based on Scotty's advice, Picard frees the sheep, the crew's main characters take a swig of the Scotch; and they all wake up in bed next to Emily Hartley.
3.24.2008 5:05pm
Sid (mail) (www):
Some of the commenters above obviously have not watched the new Doctor Who series. The effects are advanced, but the explanations are dumb-downed. The new Doctor use a professorial demeanor to look at a questioning mortal. He will pause to acknowledge the questioners remark. He will then nod his head and say "yes, but no, you are completely wrong." He then flies into a flurry of scientific terms and runs about the scene.

In the old series, the Doctor stood perfectly still and explained thoroughly the science fiction theory behind the current incident.

Now, I prefer the explanation of the past as found in The Lion King. Specifically when the wise, historian monkey wacks Simba in the head with a stick and then in response to Simba's complaint admonishes him with his own logic "what does it matter? It's in the past."
3.25.2008 8:44am
TRE:
I had the same eaction upon seeing this story.
3.25.2008 1:18pm
Gordon (mail):
Most of the comments ignore the enormity of the event mentioned in the original post.
Most stars, like our sun, burn for about 10 billion years and in that time convert five percent of their original mass into energy. A collapsing star that produces a gamma ray burst, of which this particular event is just an extreme example, converts forty percent of its mass into energy in TEN MINUTES!
3.25.2008 2:02pm
Fub:
Gordon wrote at 3.25.2008 1:02pm:
A collapsing star that produces a gamma ray burst, of which this particular event is just an extreme example, converts forty percent of its mass into energy in TEN MINUTES!
Which is why police always use no-knock warrants and SWAT teams with flash-bangs when raiding them.
3.25.2008 2:12pm
Pat C (mail):
The most distant object that can be seen with the naked eye! And it took 7 1/2 billion years to get here ! And I missed it !!!!

Damn. When's the next one?
3.25.2008 5:48pm
JeffR (mail):
An article about a similar phenomenon appeared years ago. I can't remember the title or author, unfortunately, but it was somehow related to the study of thiotimoline.

According to the article, astronomers at an observatory detected what appeared to be a supernova. Later they realized that the arrival of the light from the supposed supernova had coincided with someone striking an old-fashioned wooden match on the casing of the telescope.

One reader rejected the obvious explanation, however. Instead, he suggested that the chemicals in the head of the match had unusual endochronic properties, and that the ignition of the match had caused the supernova to have occurred millions of years in the past.
3.25.2008 10:07pm