Intergalactic Race Shows That Einstein Still Rules

Ponca City, We love you writes "The NY Times reports that after a journey of 7.3 billion light-years, a race between gamma rays ranging from 31 billion electron volts to 10,000 electron volts, a factor of more than a million, in a burst from an exploding star, have arrived within nine-tenths of a second of each other. A detector on NASA’s Fermi Gamma-Ray Space Telescope confirmed Einstein’s proclamation in his 1905 theory of relativity that the speed of light is constant and independent of its color, energy, direction or how you yourself are moving. Some theorists had suggested that space on very small scales has a granular structure that would speed some light waves faster than others — in short, that relativity could break down on the smallest scales. Until now such quantum gravity theories have been untestable because ordinarily you would have to see details as small as the so-called Planck length, which is vastly smaller than an atom — to test these theories in order to discern the bumpiness of space."

Comments

i'm confused

[circletimessquare]

they arrived within 9/10th of a second of each other

which indicates the opposite of the story's summary

Re:i'm confused

[selven]

Probably gravitational lensing making some of the gamma rays more curved than the others. Or whatever event caused them is not instantaneous (like every other large-scale event in existence).

Re:i'm confused

[DreadPiratePizz]

Over 7.8 billion light years, a difference of 9/10 of a second is such an incredibly small margin.

Re:i'm confused

[Nevynxxx]

I'm guessing that the error bounds on the readings were great enough that 0.9 seconds over 7.3billion years, was within them....

Re:i'm confused

[oodaloop]

Probably due to the reflex time when they started and stopped their stopwatches.

Re:i'm confused

[schnikies79]

If it wasn't instantaneous, or nearly, how can we even use this data? They could have been released minutes or more apart.

Re:i'm confused

[eldavojohn]

The importance is that that puts the effect at smaller than a planck length (which is the assumed smallest possible distance that something measurable can happen in classical physics). From the first article:

The spread in travel time of 0.9 second between the highest- and lowest-energy gamma rays, if attributed to quantum effects rather than the dynamics of the explosion itself, suggested that any quantum effects in which the slowing of light is proportional to its energy do not show up until you get down to sizes about eight-tenths of the Planck length, according to the Nature paper, whose lead author was Sylvain Guiriec of the University of Alabama.

Granted they say it would have to be proven much smaller than a planck length for most people to accept this as empirical proof, it is empirical data backing Einstein. The 9/10s could be due to the explosion or a physical effect but the latter is now more unlikely given the many light year distance.

Re:i'm confused

[Anonymous Coward]

The light propagated through space for 7.3 billion years. A delta of +/-0.000000000000000039% is not even close to statistically significant. It could have been from local variations in the density of a nebula or something.

Re:i'm confused

[zerosomething]

9/10th of a second is only about 3/4th the distance from earth to the moon. I don't know for sure but I think that's a rather small difference and could be accounted for just by the size of the star that exploded. Our own sun is about 4 seconds across isn't it?

Re:i'm confused

[John Hasler]

> Probably gravitational lensing making some of the gamma rays more curved than
> the others.

No. Gravity has exactly the same effect on all photons. However, the photons were emitted over a period of several seconds.

Re:i'm confused

[hotair]

That was my thought exactly. Then it occurred to me that an exploding star might actually have diverse points of origin as far apart as 0.9 light-seconds. If 7.3 billion light-years of travel is insufficient to create greater divergence than 0.9 seconds, we may have to wait for a much more distant event. My guess is that they decided that the noise of diverse points of origin sufficiently overrides the question of 0.9 seconds to the point that absent other evidence, it confirms rather than invalidates the theory of relativity.

Re:i'm confused

[natehoy]

Actually, it really indicates nothing, except that any "bumpiness" of space doesn't have a profound effect on the speed of light within the wavelength range tested. It's good data. However, this neither proves nor disprove there was an effect, just proves that the effect (if it exists) is very insignificant at the tested wavelengths.

Insignificant != Nonexistent
Tested Wavelengths != All Wavelengths

In order to prove or disprove the theory that light changes speed based on wavelength or other factors, you'd need to be sure that both pulses started the race at the exact same moment, that the two pulses travel through the same space without interfering with each other,and that they complete the race at the exact same moment (ie, within the margin of error of your testing equipment). The margin was almost one second, which is terribly insignificant when compared to 7 billion years, of course, but demonstrates clearly one of the following three things:

1. The pulses left about a second from each other, which we can neither prove nor disprove.
2. The test equipment was flawed and they really did arrive at the exact same time (which leads to #1, maybe they left at different times and just happened to arrive at the exact same moment).
3. The speed of the various wavelengths WAS affected by "space potholes", but it took 7 billion years to accumulate less than one second of variance.

If #3 is possible, which it still is even after this test, then the theory of bumpiness of space has not been disproven, it just appears that evidence points toward the bumps being really, really small or somehow only marginally effective at affecting the speed of light.

Plus, the original article goes on to explain that the tested wavelengths were relatively large, and that much smaller wavelengths might be more susceptible to the "bumpiness" of space depending on the size of the bumps. If the bumps are really tiny, then they might have just tested wavelengths that were too large to be affected by them. If we can measure some really high-frequency (low-wavelength) pulses against the ones we think are nearly identical, that would be much more compelling data.

Re:i'm confused

[sdguero]

Yes but that small of a difference (9/10th of a sec) across a a spectrum covering millions of magnitudes across almost 8 billion light years of space and time means the change is occurring at levels less than the plank constant, i.e. it confirms Einstiens traditional understanding which doesn't worry about the chop at lower levels (since the change is soooo small), AND it pushes our grasp of the under pinnings of the universe a little further along (by confirming and helping refine other quantum theory measurements). Anyway, I thought TFA was cool... :)

Re:i'm confused

[MightyMartian]

It's not the distance, it's very likely that the different photons were emitted at slightly different periods during the burst. It would be like two cars leaving a parking lot, one after the other, and both traveling at the same speed. Obviously the one behind the other will never overtake it.

Re:i'm confused

[JamesP]

You sir, are a true scientist.

I'm really tired of "skeptics" that in reality don't want to see anything.

A true skeptic would not suddenly ignore every other event where there has been a different in arrival times (similar to these), with some lame excuse. But that's exactly how TFA sounds.

Re:i'm confused

[Anonymous Coward]

9/10th of a second is only about 3/4th the distance from earth to the moon. I don't know for sure but I think that's a rather small difference and could be accounted for just by the size of the star that exploded. Our own sun is about 4 seconds across isn't it?

The speed of light = 299 792 458 m / s (commonly 3.0 * 10^8 m/s)
The average centre-to-centre distance from the Earth to the Moon is 384,403 kilometres
(384 403 kilometers) / the speed of light = 1.28223039 seconds

The diameter of the sun = 1391000 kilometers
(1392000 kilometers) / the speed of light = 4.64321221 seconds

Either you do good math in your head, or I respect your physics teacher for teaching you such interesting facts.

Re:i'm confused

[JamesP]

Thank you!

Not to mention other events where this effect has been much more exaggerated.

Re:i'm confused

[arun84h]

His in-head rounding skills, however, were taught by Lorena Bobbitt.

Re:i'm confused

[Tiger4]

You read the article. Obviously, injecting evidence and facts into the discussion is not helpful with the wild speculation, conjecture and skepticism of the uninformed.

Re:i'm confused

[mhaskell]

Possibly female photons? Their line was longer to get out of the star.

Re:i'm confused

[Anonymous Coward]

So...just to be difficult...is it worth pointing out that the measurement of the distance is dependent upon an assumption of the constancy of the speed of light? FWIW, I fully believe the laws of physics haven't "changed" over the course of the history of the universe, but if you're trying to argue with someone who believes that the speed of light isn't constant, I'm not certain how this helps. Of course, for people who actually are interested in real science, it's a useful and important result, but it doesn't seem likely to convince a disbeliever

Re:i'm confused

[AndrewNeo]

4.64 seconds

Re:i'm confused

[FlyingBishop]

It doesn't prove that the speed of light is constant, but it does reasonably prove that the speed of light is independent of wavelength, since they left from the same source at the same time.

Re:i'm confused

[Rary]

We know that the pulses were caused by an event that lasted 2.2 seconds, therefore we know that they left anywhere from 0 to 2.2 seconds apart. However, the point isn't to determine a simple boolean result to the question "did they arrive at the same time", the point is to invalidate the predictions of theories. The existing theories predicted that the arrival times of these pulses, having left at most 2.2 seconds apart, would be at a minimum significantly more than 0.9 seconds. However, they were not, therefore the theories' predictions are wrong, and thus the theories are invalid. The one theory that predicted that they would arrive at most 2.2 seconds apart remains — not proven, but still not disproven. That's how science works.

Re:i'm confused

[Anonymous Coward]

"When you have a period, chop it off?"

Re:i'm confused

[radtea]

I don't know for sure but I think that's a rather small difference and could be accounted for just by the size of the star that exploded.

You're confused because the summary, and the press release on which it is based, are misleading and wrong.

This is a gamma ray burst (GRB), which originate from neutron stars, not a super-nova (which is the only reasonable meaning one can give "exploding star".) Neutron stars are small, resulting in much finer burst timescales.

The paper discusses the time-structure of GRB's, which has been extensively studied. The fundamental result they get is from a single high-energy gamma ray at the end of the last spike in the burst, which comes 0.9 s after the onset of that spike (seen in the lower-energy photon flux). They do a lot of analysis to argue that the most plausible explanation of that single photon is that it is a member of that spike rather than a random cosmic ray. Anyone familiar with modern statistical techniques will see that this is straightforward, albeit non-trivial.

This is the way science works: we squeeze limited and imperfect experimental evidence as hard as we can using established theory and other, supporting, observations. All the "yeah, well, it could be something else" kind of commentary we see so much of on /. is irrelevant to the scientific process, because it is doing nothing but repeating what everyone already knows: sometimes the most plausible explanation turns out to be wrong.

The exciting thing about this measurement is that they have shown it is possible to put quantum gravity to a rather good test using entirely conventional gamma-ray spectroscopy techniques, and repeating this kind of measurement over the next few years or decades on different bursts will rapidly push down the limits on potential planck-scale effects, because eventually we'll see bursts where there are a few high-energy photons closer to the onset, or we will see bursts from objects at larger (known) distances.

The present authors argue, rightly, that their observation makes theories that have a linear dependence of light velocity on wavelength less plausible. At some point in the next few years it is likely that those theories will be dead, and there's really nothing so beautiful as a theory killed by a fact.

Re:i'm confused

[Geoffrey.landis]

they arrived within 9/10th of a second of each other

which indicates the opposite of the story's summary

Notice the key word here, "within".

One second in 9.3 billion years is a pretty good measurement. It indicates a difference in speed of no more than 0.0000000000000003 percent.

Re:i'm confused

[darsal]

An engineer, a mathematician, and a physicist are riding a train through Scotland.

The engineer looks out the window, sees a black sheep, and exclaims, "Hey! They've got black sheep in Scotland!"

The mathematician looks out the window and corrects the engineer, "Strictly speaking, all we know is that there's at least one black sheep in Scotland."

The physicist looks out the window and corrects the mathematician, "On one side."

Re:i'm confused

[LordLimecat]

No. Gravity has exactly the same effect on all photons

How do we know this is true over long distances? Seems to me a lot of this is conjecture.

Re:i'm confused

[MillionthMonkey]

they arrived within 9/10th of a second of each other ... which indicates the opposite of the story's summary

1. One leaves from near one pole. One leaves from near the other pole. Or any two antipodes depending on where the Earth is. Even from a star comparable to the size of the Earth-Moon radius exploding, 0.9 seconds is quite reasonable.
2. Near the explosion there are also going to be elastic collisions between the gamma rays and the neutrons that are being created en masse. The likelihood of photon-neutron collisions is dependent on the photon wavelength.
3. The explosion lasted a frigging 2.2 seconds.

The only valid observation is that the story's summary did not indicate this, but anyone with a brain... oh never mind.
0.9 seconds is pretty good. Someone mod this first-post-contrarian parent down from "Insightful" and maybe the next two page loads will stop seeing that within 9/10 of a second of each other.

Re:i'm confused

[LordLimecat]

You possibly have the most relevant post in this entire conjecture filled thread. We have no way of PROVING anything with this data, because the only things it could prove or disprove are the theories that would be used to interpret the data in the first place (speed of light, distance, etc). It can further validate things, or show the insignificance of the effects mentioned on the speed of light. Its really obnoxious to hear people claiming that because there is discrepancy in the reading, but certain effects can produce discrepancies, that necessarily these effects which caused the observed discrepancy.

Re:i'm confused

[steelfood]

Granted they say it would have to be proven much smaller than a planck length for most people to accept this as empirical proof

You mean most physicists. Most people couldn't tell you what qualifies as empirical proof, much less what planck's length is, if it hit them on the head.

Re:i'm confused

[Cyner]

Exactly.

Competing theories stated the difference would be more than 3.1 seconds (The possible variance given a 2.2 seconds event and 0.9 seconds difference). Therefore they are invalid.

Einstein stated the total variance would be equal or less than the total duration of the event. Total duration was 2.2, difference was 0.9, this fits. Einstein's theory is not proven invalid.

Any other conculsions are logical falacies.

Re:i'm confused

[The_Wilschon]

In short, .9s is well within the uncertainty on the measurement, and from that uncertainty, you can decide which class of quantum gravity theories your experiment is sensitive to. If you had a theory that said the deviation should be .000001s at these energies, then this experiment would never be able to say anything about that theory. But we have otherwise good theories of quantum gravity that claim the deviation at these energies should be much larger than the experimental uncertainty. This experiment falsifies those theories.

Credentials: Two guys in my group (CDF and Fermi) have worked on this very analysis. One of them worked on it just for this past summer (and didn't get too far, really), and the other used it for his thesis (graduated last summer).

Re:i'm confused

[Anonymous Coward]

No, the article is stating that the theories in question predicted much larget effects.

It's a simple matter of setting bounds on your start stop time (which they can) curveture of space, blah blah blah (I'm an engineer not a physicist)...

The long and short of it is this: If these physicist are any sort of scientists they have calculated the bounds that could prove or disprove the theory. The data that they got fell outside of the bounds that validate the theory so the theory is considered invalid.

They even go on to state that while its a start, they will need to collect additional data which they believe they will be able to get from the very same source. So the whole: These men aren't real scientists garbage isn't even based on what was in TFA. Go RTFA again and stop spouting your highschool physics awesomeness and let the real scientists get to work.

Re:i'm confused

[ultranova]

No. Gravity has exactly the same effect on all photons

How do we know this is true over long distances? Seems to me a lot of this is conjecture.

Strictly speaking: we don't know it. However, all evidence so far points to that direction, and none points to the other, so it's the best educated guess we can make at this point.

This gets us to the fascinating but pointless philosophical question about how it's possible to know anything, since you never know if you can trust your perceptions and thought processes.

Re:i'm confused

[dumuzi]

Would you know a what a planck length is if it hit you on the head?

Being hit on the head by a plank length could be empirical proof that getting hit on the head sometimes hurts.

Re:i'm confused

[JamesP]

No, the article is stating that the theories in question predicted much larger effects.

The data that they got fell outside of the bounds that validate the theory so the theory is considered invalid.

Then what about this? http://www.physorg.com/news110480559.html

There are several aspects to be considered, of course.

Go RTFA again and stop spouting your highschool physics awesomeness and let the real scientists get to work.

Well, too bad I have a bachelor's degree and actually have studied relativity and QM. Also, you're the anonymous coward here.

Re:i'm confused

[Anonymous Coward]

The diameter of the sun = 1391000 kilometers
(1392000 kilometers) / the speed of light = 4.64321221 seconds

Either you do good math in your head, or I respect your physics teacher for teaching you such interesting facts.

-_-

Re:i'm confused

[Anonymous Coward]

Perhaps do not understand the meaning of the word 'within'.

Re:i'm confused

[Anonymous Coward]

A correction, the leading theory of gamma ray bursts involves collapsing stars (hypernovae or collapsars), not neutron stars.

Re:i'm confused

[shaitand]

"smaller than a planck length (which is the assumed smallest possible distance that something measurable can happen in classical physics)"

Something seems to be amiss here. If the variation is smaller than a planck doesn't that debunk aforementioned assumption?

Re:i'm confused

[kmac06]

No, the error bounds can easily be within 1 ns for off-the-shelf photon detectors (though that's for optical wavelengths, not gamma rays, but I'm sure the gamma ray detectors aren't 900 million times slower). TFA says (or at least implies) that the time separation is due to the length of time the gamma ray burst was "on".

Re:i'm confused

[ceoyoyo]

"This is a gamma ray burst (GRB), which originate from neutron stars, not a super-nova (which is the only reasonable meaning one can give "exploding star".) Neutron stars are small, resulting in much finer burst timescales."

You should be more specific. Short gamma ray bursts (which this seems to be) are most likely produced by compact objects like neutron stars. Long gamma ray bursts look like they probably originate in certain kinds of supernovae.

Re:i'm confused

[Anonymous Coward]

I'm guessing that the error bounds on the readings were great enough that 0.9 seconds over 7.3billion years, was within them....

No it isn't. There is a single point of collection from Nasa, the 7.3 billion years of travel is completely irrelevant at the point of measurement, it may as well have been .0000001 of a second of travel, if there equiqment is so shitty that .9 of a second is an acceptable error for the times of when 2 events occur then I doubt anything else coming out of there could EVER be trusted.

Re:i'm confused

[HydroPhonic]

It might be that the photons in question took slightly different paths through the myriad gravity wells there and here, such that the "distance" they traveled was not equal.

Re:i'm confused

[AniVisual]

As for how small a neutron star is, it's ~20 km in diameter.

Re:i'm confused

[Hurricane78]

Uuum, how do they know that the rays *started* at the same time? It can easily be a set of those rays of different energies starting at different times, that happened to end up here at that same time. Sorry, but there is no way in hell, they can know when those rays started. Let alone this exact.

Re:i'm confused

[Hurricane78]

And how exactly do they know that they started at the same time?? Even if they did, time warping can happen anywhere in-between. You know, like getting close to a black hole.

Ah, I know: They can't and it's bullshit!

Re:i'm confused

[Hurricane78]

The fundamental result they get is from a single high-energy gamma ray at the end of the last spike in the burst, which comes 0.9 s after the onset of that spike (seen in the lower-energy photon flux). They do a lot of analysis to argue that the most plausible explanation of that single photon is that it is a member of that spike rather than a random cosmic ray. Anyone familiar with modern statistical techniques will see that this is straightforward, albeit non-trivial.

So the assumption is, that the photons of different energies that they compared in arrival time, come from the same ray, and from the same moment in that ray's wave. And the proof for the assumption is some pretty complex statistical analysis?

Sorry, but I'm still far away from sold. Please enlighten me, how statistical analysis can determine the exact same starting time, and cope with the time-warping (that can happen near any object with a big mass) that most likely also happened? I simply can't imagine that. (This is a honest question. Not a rhetorical one.*)

I think that it's very likely, that the photons they measured, were just the set of those that arrived at roughly the same moment, because the either started at the same time, OR were time-warped, had different speeds, or whatever, which made them end up in the same time, despite having started at different ones. And without being there at the time of start, or knowing the state of all of space that the photons passed through, there is no way to ever know which of those things happened.

It would be cool though, if you could *prove* me wrong with one (logically consistent and sound) paragraph. :)
___
* From your comment I assume you're the exception here at /., and don't take everything you read as a personal attack on your beliefs. ^^

Re:i'm confused

[Sean Hederman]

Because if gravity randomly affected photons differently, our night sky would look a LOT different than it does.

Re:i'm confused

[Anonymous Coward]

The speed of light can not = the plank length any-longer. The anomaly was originally three phased and bridged a connection that caused nothing short of complete chaos. The light can reach any wavelength within any single two dimensional stretch now and of course at the speed of respective 2 dimensional "light" now. The light can speed into the 3rd dimension but when it occurs it will not create an undefined singularity. The singularity it will create can not be defined but is technically defined in and of its self.

Re:i'm confused

[mbone]

The photon timing for GLAST is supposed to be good to 10 microseconds.

Re:i'm confused

[mcgrew]

Either you do good math in your head, or I respect your physics teacher for teaching you such interesting facts.

Or he used a slide rule. We'd better get off his lawn!

Re:i'm confused

[HeadlessNotAHorseman]

Well, too bad I have a bachelor's degree and actually have studied relativity and QM

Of course, for all we know you have a bachelors degree in World History and have read "A Brief History of Time".
 
It's fun to be pedantic :)

Re:Slow news day.

[Anonymous Coward]

well if we lived in a time when water was only theoretically wet i guess that would be big news.

How do we know

[Darth Sdlavrot]

They didn't leave 9/10ths of a second apart?

Re:How do we know

[John Hasler]

Who said they didn't? The point is that even if they left at the same instant from the same point .9 seconds is much smaller than predicted by the theory in question.

Re:How do we know

[CrimsonAvenger]

Who said they didn't? The point is that even if they left at the same instant from the same point .9 seconds is much smaller than predicted by the theory in question.

No, TFA seems to say that it's slightly smaller than the theory would predict with the 0.9s difference.

But what if the photons that arrived first had left last? That might put the difference in travel time as high as 3.1s....

Re:How do we know

[natehoy]

We don't. But if we can theorize they left 9/10ths of a second apart, we can theorize they left 150 million years apart and that "space potholes" DID affect their speed to a fairly significant extent.

In other words, this data appears to indicate that any effect would be very small, but if we accept that they left at the exact same time we have a difference that must be explained. And that explanation could be evidence supporting what the article says the test provides evidence against (that the pulses left at the same time and had a variance in their arrival times, therefore their speed was affected by some factor).

And if we assume they left at different times to account for their varying arrival times, we're saying the conditions of the initial phase of the test test are unknown (which is, by the way, very true) therefore it's hard to draw any solid conclusions from the test results.

There could be a way to validate this result. Test different distances. If you test a star at, say, 15.6 billion light years away and get a 1.8 second difference, and a star 3.9 billion light years away and get a 0.45 second variance, then you can reasonably conclude that there IS an effect on speed, and it shows that space may well be bumpy, just not VERY bumpy. If you test stars at various differences and observe a constant 0.9 second variance, then you can reasonably conclude that there is no difference in speed and that some factor is releasing certain wavelengths at different times during the event, and space is looking pretty silky smooth.

Re:How do we know

[natehoy]

For the pedantics among you (myself included), please replace "15.6" with "14.6" and "3.9" with "3.65". Somehow I got "7.8 billion" stuck in my head instead of the stated "7.3 billion". Stupid brain!

Re:How do we know

[scheme]

But what if the photons that arrived first had left last? That might put the difference in travel time as high as 3.1s....

I think the scientists writing the paper and the reviewers already considered that possibility. The paper sets bounds on how big of an effect energy / speed interactions could be for photons so they probably used worst case situations to establish the upper or lower bounds as needed.

Re:How do we know

[The_Wilschon]

An extremely careful analysis would probably set much more stringent bounds. We (scientists) don't always have time to be that careful, so we generally go with much coarser estimates of uncertainties and the like, resulting in very conservative bounds.

How do they know

[2.7182]

that the photons all left at the same time?

Re:How do they know

[John Hasler]

The event was approximately 2.2 seconds long. Thus it is plausible that these two photons left .9 seconds apart.

Re:How do they know

[Richard_at_work]

Its also plausable that they left at the same time, and arrived 0.9 seconds apart. How do we tell though?

Re:How do they know

[John Hasler]

We don't, and it doesn't matter. .9 seconds is much smaller than would be predicted by the theories in question.

Re:How do they know

[pilgrim23]

they didn't. the slower one was waiting for its wife to get ready.

Re:How do they know

[noundi]

The event was approximately 2.2 seconds long. Thus it is plausible that these two photons left .9 seconds apart.

Mod parent up, obviously this is a mere effect of the size of this sun. Different layers of the sun produced different wavelenghts in the bursts as the sun would consist of various elements in layers, but you already knew this.

Re:How do they know

[sexconker]

Its also plausible that they left 2.2 seconds apart, and arrived 0.9 seconds apart in the opposite order. How do we tell though?

Re:How do they know

[Richard_at_work]

I think it is pretty much the only thing that matters - until you can say when the photons left in relation to each other, there is no way you can say the delay validates or invalidates any of the theories in question.

Re:How do they know

[2.7182]

But how do we know the length of such an event so accurately? Maybe it took 10 minutes.

Re:How do they know

[jabuzz]

Not true, if the theory requires that they would be separated by say 900 seconds, they left within 2.2 seconds of one another maximum, and we observe them at 0.9 seconds apart, then the theory is proved wrong.

Re:How do they know

[Tiger4]

Do we call in the MythBusters to stage an experiment? I need to see a Confirmed, Plausible, or Busted branding iron before I believe anything.

Re:How do they know

[gnick]

Not true. If we know that the event that generated the rays lasted only 2.2 seconds and we have a theory that would delay one of the rays by more than 3.1 seconds (2.2 + 0.9) relative to the other, we can invalidate that theory. From my understanding, that is exactly the case we're dealing with. You are correct though that this cannot completely validate any specific theory - All it can do is reinforce the assumption that our current theory is more accurate than some others proposed and eliminate some competing ideas.

Re:How do they know

[publiclurker]

Jamie wants BIG boom!!

Re:How do they know

[csartanis]

Perhaps your theory is _not_ plausible, and the scientists know more than the average slashdot commenter?

Re:How do they know

[mikael]

What if there was only one super-high-energy photon that left the supernova, and collided with an proton creating two gamma rays later on?

Re:How do they know

[selven]

So God runs the universe using Verizon technologies?

Re:How do they know

[KillerBob]

We're talking about a distance of 7.3 billion light years. Even if the expected difference in speed is 1m/s (absolutely miniscule difference against the speed of light), we're talking a difference significantly greater than 3.1s in travel time.

Re:How do they know

[Anonymous Coward]

Because it is incredibly unlikely that:
1) the event lasted 10 minutes
2) produced gamma rays steadily decreasing in energy
3) such that the effects of the difference of the speed of light on the particles over 7.3 billion years would compress the burst to 2.2 seconds
4) that we would be located at the exact location to observe a burst of only 2.2 seconds (closer or farther away and the burst would still be spread out)

Since all gamma ray bursts are short and have different energy radiation, there are only two possibilities. Either space time is not bumpy at plank distance, therefor the speed of light is not dependant on wavelength, or we are magically located at the perfect distance from gamma ray burst events that they all compress to such a short time, requiring divine providence to explain the happenstance.

Re:How do they know

[LordLimecat]

Your post makes sense except that "more accurate" implies that "proved wrong tomorrow" is somehow better than "proved wrong today". Either its right, and will never be proved wrong, or it is wrong, and may eventually be proved as such.

Re:How do they know

[Dare nMc]

Makes me wonder how, and how long they were looking for this. It seams like a whole stream of photons could have bounced off a celestrial body 2000 light years away, and the faster light stream came past earth 2000 years ago as well (and the slower stream will reflect from the same source, and come by us in 2000 years.) If they were just looking for a stream of photons within 1 second of each other, eventually we were likely to find proof, even if Einsteins theory was wrong.

Re:How do they know

[Anonymous Coward]

That case in highly improbable as conservation of momentum requires the two photons to be produced in opposite directions.

Re:How do they know

[LordLimecat]

How can they know the length of the event? The particles were RECEIVED over a space of 2.2 seconds. The issue is that the only information we have (that i could see in the article) is based on EMS signals, and that any inferences we draw from that data will RELY on our theories on how EMS signals move and behave. If Einstein is completely wrong, and if gravity works in vastly different ways at larger scales, we have no way of validating or refuting any of those based on THIS data. What if the higher energy signals were released much later, but traveled faster, so that it appeared to be a 2.2 second event?

Re:How do they know

[LordLimecat]

Wouldnt the theories be wrong, just on a different scale than predicted, if the more energetic signals had different travel times?

Re:How do they know

[LordLimecat]

If only that sort of rebuttal were how scientific theories were validated, imagine the progress we could make. "Of course my theory makes sense, I'm smarter than you!"

Re:How do they know

[DigitalPasture]

GRBs to the best of my knowledge release (at least) two separate bursts at different energy levels at separate intervals... One (at least) high energy, the other lower. I'm guessing that's where the delay figures in. I believe the lower energy burst is referred to as an "afterglow". That's from memory, so I may be off.

Re:How do they know

[svtdragon]

Clearly. It took 7.3 billion years for the data to get here. Sounds on par with Verizon to me.

Re:How do they know

[krlynch]

They didn't, but that doesn't matter to the argument :-)

We know from more nearby GRBs that photons at all energies are emitted throughout the "explosion". That is, high energy photons aren't emitted earlier than lower energy photons. In other words, if you look at the mean emission time for all photons from energy, say, 10keV to 11 keV, and for those from energy 10MeV to 10.1MeV, (and every other energy band), those means are all the same.

Now, if HIGHER energy photons covered the distance faster than lower energy photons, then the MEAN arrival time of those same energy bins would spread out. What these observations showed is that the highest observed energy band and the lowest observed energy band spread out by no more than 0.9 seconds over 7.3 billion years. The "no more than" is the important part ... it's actually technical jargon that means "the result is consistent with zero, but since we only observed a small number of events, we can only statistically conclude that the spread was less than 0.9 seconds", typically with 90% or 95% confidence.

Re:How do they know

[gnick]

Your post makes sense except that "more accurate" implies that "proved wrong tomorrow" is somehow better than "proved wrong today".

"Proved wrong tomorrow" IS better than "proved wrong today". "Proved wrong tomorrow" means that we've got nothing contradicting it yet and it's the best we've got. I'm perfectly happy to accept that everything we know is wrong and go through life using our best-available models for how the world works. If you wait for a perfect model of everything before you start using the models at hand, you'll never get anything done. So what's wrong accepting what we've got as a possibly-flawed, but best-available model and refining it as we learn more?

Either its right, and will never be proved wrong, or it is wrong, and may eventually be proved as such.

You left out an important option. There's "right", "wrong", and "unproven but useful and not yet proven wrong". Very few things in science or life can really be "proven" right. A lot of science is made of reasonable (sometimes radical) guesses that haven't yet been discredited. Even the "law" of gravity is still just a theory, but that fact doesn't make me mistrust my scale because we may be able to refine our knowledge of heavy-body attraction in the future.

Re:How do they know

[SleazyRidr]

We all know that isn't the way science is done, but I (and a lot of other people) get rather pissed off by the inevetable commenters who read the summary and then seem to think the researchers are retarded monkeys who didn't finish high-school. They've spent a long time on this, they've thought out a lot of possibilities, you aren't going to prove them wrong with your 30-second insight.

Re:How do they know

[bidule]

0.9 seconds over 7.3 billion years is... at most a 10^-16 speed difference. IOW, the speed of light is not affected by the wavelength.

Suppose there was a negligible 1 in a million speed variation between those wavelengths, and this speed variation occurred in a magic part of space representing 1 millionth of the total distance. We'd still get 2-3 days of lag between our reception of both wavelengths.

That should tell you why your question is meaningless.

Re:How do they know

[MikeBabcock]

Nobody has to be right for another to be wrong.

To be honest, my only problem with this entire scenario is the proof that the event was in fact less than 2.5 seconds long. I'm slightly curious how we can know this out of band, that is to say, from data other than that which we're already unsure of how to measure.

Re:How do they know

[DragonWriter]

I think it is pretty much the only thing that matters - until you can say when the photons left in relation to each other, there is no way you can say the delay validates or invalidates any of the theories in question.

But we do know that -- to a certain degree of accuracy. Now, its not enough accuracy to say that the photons took the exact same time to travel the exact same distance (which would require the always-unattainable perfect accuracy), but its enough to say that the difference in the travel time was not sufficient to be consistent with the theories at issue.

Re:How do they know

[CharlyFoxtrot]

Its also plausible that they left 2.2 seconds apart, and arrived 0.9 seconds apart in the opposite order. How do we tell though?

There would be interference if that had happened. Also you would expect there to be a model for this sort of event that would tell you when the high energy bursts and when the low energy bursts would take place.

The paper itself unsurprisingly seems more nuanced than the summary: "The spread in travel time of 0.9 second between the highest- and lowest-energy gamma rays, if attributed to quantum effects rather than the dynamics of the explosion itself, suggested that any quantum effects in which the slowing of light is proportional to its energy do not show up until you get down to sizes about eight-tenths of the Planck length, according to the Nature paper." In other words : macro scale Einstein is still valid and micro scale effects if they exist are vanishingly small and put new limits on theoretical speculation.

Re:How do they know

[Terwin]

Don't forget another possibility:
Not the most accurate model available, but both simple enough and accurate enough to be useful for the application at hand.

Newtonian models of gravity are still used for most (all?)space exploration. Sure it does not cover Frame Dragging, but the error bar between Newtonian gravity and general relativity is small enough in most cases that it is not worth the additional effort of using the greater complexity of general relativity instead.

Re:How do they know

[Anonymous Coward]

Indeed. I think those two rays may actually be coming from two different bursts (traveling at different speeds) which by sheer coincidence happened to arrive at almost the same time at the detector.

Re:How do they know

[RealGrouchy]

Mythbusters already tested this. The episode will air 7.3 billion years from next week.

- RG>

Re:How do they know

[lgw]

Science doesn't deal in "proven right" and rarely in "proven wrong". That would be math with the proofs. Science deals in "accurate over the available data", and looks for "more accurate" models over time.

Re:How do they know

[Anonymous Coward]

It's just a metal plaque. If it was a branding iron, the letters would appear backwards on the plate.

Re:How do they know

[Kagura]

IOW, the speed of light is not affected by the wavelength.

But actually, it's a well-determined phenomenon called "Dispersion". SETI has to run special filters against their signals to correct for higher frequency waves traveling slower than low frequency waves from the same event, since they get mashed together due to the speed difference over the distances involved.

Re:How do they know

[asaz989]

The event lasted 2.2 seconds - we don't know *when* in the event these particular two photons were released. They could have been released simultaneously, or they could have been released 2.2 seconds apart, or anything in between. This doesn't prove that the photons traveled at exactly the same speed, it just disproves theories that would indicate a speed difference of more than (.9 seconds)/(7.3 billion years) - which I presume they do.

Re:How do they know

[easyTree]

It took 7.3 billion years for the data to get here. Sounds on par with Verizon to me.

Ahh... but did the intergalactic delivery guy beat the crap out of the recipient?

Re:How do they know

[billcopc]

"Proven wrong tomorrow" is worse, because it means we're ignorant for one day too many.

Re:How do they know

[MaskedSlacker]

I hope your science profs failed you, because you don't understand science.

Everything in science is WRONG, strictly construed. Newton's theory of gravity is WRONG (gravity is not proportional to 1/R^2), but it's reasonably close for many applications. Einstein's theory of general relativity is WRONG, strictly construed, but it is LESS wrong than anything else we've managed to come up with (for certain applications).

Science is the continual quest for explanations that are less wrong, not right ones. Even if we found THE right answer, we'd never know it. We'd only ever be able to know that it was the least wrong answer ever thought up.

Re:How do they know

[bronney]

I wish i have mod points bro. bravo!

Re:How do they know

[bronney]

Another great post. Thank you. That last bit is the real.

Re:How do they know

[Anonymous Coward]

"If we know that the event that generated the rays lasted only 2.2 seconds"

Seems to me that's a big if. How do we know that it lasted 2.2 seconds? I hope the answer isn't by the light emissions given off.

Re:How do they know

[Anonymous Coward]

What? Gravity is inversly proportional to R^2 to a rediculous amount of precision. So it works for a lot more than "many applications."

Re:How do they know

[MaskedSlacker]

And yet such a theory fails to account for the perihelion shift of Mercury, so it is, strictly speaking, wrong. Just like everything else in science. Science is a progression of best guesses, that are all ultimately wrong but each is progressively closer to being right than the last.

Re:How do they know

[bidule]

I'm sorry I only dealt with spherical cows. For me, space is a perfectly empty medium with n=1.

Re:How do they know

[Anonymous Coward]

Electromagnetic dispersion is not really under study here anyway; the relevant question is the redshift independence of the gap between the (relative) HF/LF pulse pairs associated with GRB sources that we've seen at lower redshifts.

Also, the question is not about the qualities of free space, but rather those of spacetime (more technically, do different mass-energies follow the same geodesics). Frequency is interesting because of E = sqrt((h/lambda . c)^2 + (mc^2)^2), i.e. higher-frequency photons have greater mass-energy, so a box of high-frequency gamma rays will have more mass-energy than a box of low-frequency gamma rays. When launched serially, do these boxes maintain a constant separation across great distances? Except that the distances involved necessarily involve spacetime curvature (because of the metric expansion of space), this question is effectively in the weak-field limit, so even Newtonian mechanics would say: "yep, ceteris paribus the two boxes should maintain a constant separation".

Different hypotheses of gravitation and motion have arisen which predict that the distance between the two boxes should decrease across long distances because (for instance, and put very simply) there is a hidden drag term not captured in the Einstein stress-energy tensor that is mass-energy dependent in the limit of high particle energies. That is, the first box of high-energy photons would slow down over long distances. Physically we would see that as interference. (If there were a hypothetical framework in which there is greater drag on lower-energy particles that could preserve the large scale structure of the matter in the universe that we see in the sky, then we would also expect to see a much larger gap between the two boxes of light launched from a distant source than the two boxes of light launched from a closer one).

Also, did you actually read the paragraph your link goes to: "The dependence of the speed of light in a material..."

Free space is not a material, by definition. Intergalactic space is a very close approximation to free space. Certainly from studying spectral lines we know that the frequency dependent refractive index (n) is 1 to many digits of precision even to events at high redshifts, which accords with the defined relative permittivity and relative permissivity of free space.

High redshift dispersion would smear out our telescopic view of distant galaxies much more than gravitational lensing ever would. After all, dispersion *disperses* photons along multiple, different-length paths, because of collision, compton scattering, and other similar effects.

Dispersion is simply not a factor -- space is not a dispersive medium. Which is good, because space is not supposed to be a medium at all, if it is to be considered a very good approximation of free space.

That said, there are many radial paths which are occluded by dust, gasses, and other things in the interstellar medium that are dispersive media. The dispersion is greater between very high frequency photons and very low frequency ones, in part because the latter have been subjected to compton scattering, astrophysical ASE, and other individual-photon mechanisms that contribute to lengthenings of path and lengthenings of wavelength that are seen as dispersion macroscopically.

The area intersected by our detecting instruments at this radius from a pointlike omnidirectionally radiating source is so tiny, that the flux of photons which fall back onto those areas after undergoing dispersive events will be microscopic compared to the flux of photons which were always on-axis, because of the extra degrees of freedom available to the former set.

Moreover, the GRB follows the two-peak pattern seen in those with much lower redshifts (i.e., closer events).

Consequently, it is safe to say that the photons detected in the relevant frequency ranges travelled essentially the same geodesics from a two-pulse event. However, recorded data will be scrutinized for lower-freque

Re:How do they know

[Anonymous Coward]

Now, if HIGHER energy photons covered the distance faster than lower energy photons

Spacetime theories where discretization happens at larger than Planck length scales predict that higher energy particles will be slowed by nonsmoothness in spacetime, whereas the EFEs are smooth continuous equations. The hypothesized discretization would occur at very small length scales and thus produce changes in the fields (particles being excitations of the fields) proportional to to the strength of gravitation compared to that of the other fundamental forces (i.e., < 1e-25 of the weak force, < 1e-38 of electromagnetism). However, this does alter the underlying geodesics along which excitations in the fields would propagate, with spatially large excitations propagating across the underlying lumpiness with a G-like acceleration felt through the whole excitation, and spatially compact excitations bending around the underlying lumpiness and feeling a greater accleration. From our view, this means spatially larger photons (longer wavelengths) would arrive before spatially smaller photons (shorter wavelengths). If we used geometrized units (G=c=hbar=k_b=1) and embedded a clock in each photon, the clocks in the higher-energy photons would be running slow compared to those in the lower-energy ones, which would violate the equivalence principle; the slowdown would be nonlinear: effectively zero until particle energies reach the discretization energy of the underlying space time, then increasing with increasing particle energies. The greater the slowdown, the later the arrival at the detector. Moreover, the longer the geodesic, the more space-time discretization intervals are crossed, leading to a greater slowdown still. Consequently, a faraway source would show a greater slowdown for high energy photons than a nearer one; moreover there would be a lyman-alpha like chunking of the photon flux because of the Hubble flow (i.e., high energy photons from source to our detector will be slowed down for a while by both the metric expansion of space (large scale spacetime curvature) and the underlying discretization of spacetime (small scale spacetime curvature), but would transition below the latter scale and then only be slowed down by the metric expansion. This would result in interference fringing when looking at high-redshift source light.)

Aliens certify Einstein?

[DustCollector]

Did anyone else read this headline about an intergalactic people verifying Einstein's theories?

Re:Aliens certify Einstein?

[Anonymous Coward]

NO, it's about aliens invalidating Einstein's sanity...FROM BILLIONS OF YEARS IN THE PAST

Re:Aliens certify Einstein?

[natehoy]

[required slashdot meme]

I, for one, welcome our Einstein-validating overlords.

Re:Slow news day.

[VShael]

That would be big news, if some smart people had put forward the idea that water, at the molecular level, isn't wet.

(Which it isn't, by the way.)

how do we know

[Anonymous Coward]

that these rays are all from a star which exploded 7.3 billion light years away? what was monitored to predict arrival?

Re:Slow news day.

[Anonymous Coward]

Do we really, we need an article that says

SCIENCE, bitch.

Re:Slow news day.

[selven]

So an article about the four color theorem being proved is irrelevant because we were already 99.999% certain before it happened?

And in related news...

[e9th]

Einstein is no. 9 on Forbes magazine's list of top-earning dead celebrities, nestled between Dr. Seuss and Michael Crichton.

Re:And in related news...

[CarpetShark]

I was going to say that this:

Einstein Still Rules

must be how god myths start.

Einstein is no. 9 on Forbes magazine's list of top-earning dead celebrities

Now he's earning money in death too?

Re:Slow news day.

[Tibia1]

What a time we live in where a "slow new day" consists of a 7.8 million year race being recorded (regardless of the results), a fusion reactor is being developed, and a real time speech translator was released.

Maxwell, not Einstein

[Anonymous Coward]

Should this give props to Maxwell, rather than (or in addition to) Einstein?

Re:Maxwell, not Einstein

[conureman]

Most people think J.C. Maxwell helped Ringo with percussion on "Abbey Road". Einstein has Box Office Mojo.

Re:Slow news day.

[Anonymous Coward]

Some people just like to get offended. It validates their existence.

So-Called?

[Afforess]

I'm curious, why is the Plank-length "So-called"? Hasn't it been firmly established as a unit of measurement?

Re:So-Called?

[Compholio]

I'm curious, why is the Plank-length "So-called"? Hasn't it been firmly established as a unit of measurement?

It's a unit of measurement derived from dimensional analysis. Some believe that the Planck length is the unit that describes the quantization of space, but this assertion has not successfully been tested.

Re:So-Called?

[JasterBobaMereel]

...It's so small they we don't have anything that can even come close to measuring anything even close to this length, so anything said about conditions at this length is untested (and possibly untestable?), and what we have that explains what happens at these distances (mostly quantum gravity) are highly speculative and many of the hypotheses are contradictory ...

This is an actual case of science being "only an hypothesis" that actually equates to the reporters "Only a theory" ..But this experiment probably discounts at least a few of the flavours of quantum gravity that have been proposed

Re:So-Called?

[rossdee]

Because the Planck length is too small for the american media (and people) to imagine, it will never end up replacing the standard unit of length which is of course the football field.

Re:So-Called?

[Anonymous Coward]

I'm curious, why is the Plank-length "So-called"? Hasn't it been firmly established as a unit of measurement?

Because a plank is only as long as you cut it?

Re:Slow news day.

[Anonymous Coward]

The summary was poor, but so was the article. This should have been more an article about quantum gravity and how one of the theories is potentially wrong and how there are more tests coming.

One interesting thing that stood out is they used the assumption that the effect of quantum gravity would be proportional to the energy of the light; is this what the theories suggested or is this another case of science getting lost in the translation to newspapers?

A decade long project

[mbone]

This was proposed by G. Amelino-Camelia et al. back in 1998; here is a review from 2004. Even though the wavelengths of even the most energetic gamma rays are much, much, longer than the Planck length, roughness in space time at the Planck length adds up over cosmological distances, and could be in principle detectable. (The Planck length can be thought of heuristically as the length at which the gravitational effects of virtual particles should be strong enough to create virtual black holes; general relativity cannot be ignored in quantum mechanics at that scale, and vice versa.) What this current test is ruling out is a particular violation of Lorentz invariance - a variation of photon speed with energy. There were similarly negative results using radiation from the Crab nebula in 2003.

It should be noted that this does not rule out quantum gravity - it seems pretty clear that General Relativity and Quantum Mechanics cannot both apply at the Planck scale. What this work is doing is beginning to constrain models of quantum gravity (there is as yet no general theory that makes precise predictions). What would be really cool is to detect some effects, which would maybe help nudge the theorists along.

Re:A decade long project

[Xenophon Fenderson,]

Would someone please explain in terms comprehensible by a non-specialist (me) why GR and QM are incompatible? I keep reading this assertion, but I don't really know enough about the details of either theory to understand why they are incompatible.

Re:A decade long project

[ceoyoyo]

The usual high level explanation is that GR assumes space is perfectly smooth. It curves, in response to gravitational effects, but it's smooth. That assumption has various consequences for the theory. If you don't have it, GR starts to give weird results, including lots of infinities which are a pretty good indication that your theory has a problem.

Quantum mechanics on the other hand demands that space, on very small scales, be very not smooth. If you look very closely at a little bit of space (i.e. make a very precise measurement of length) the uncertainty principle says that your measurement of energy will be very imprecise. The potential for lots of energy means that there may be massive virtual particles popping into and out of existence. If you look close enough, there should be enough energy density to form black holes.

Re:A decade long project

[mbone]

Here is a basic level answer - in quantum mechanics forces result from the interchange of particles in a flat background space time. In general relativity, forces result from the curvature of space-time, and matter (and all mass energy) cause that curvature, and thus cause their own motion. These are rather different ways of looking at the universe, but in both theories you calculate things using differential equations (i.e., you assume that spacetime is smooth at a small enough scale, so you can deal with differential quantities). In Quantum Mechanics there is a inherent uncertainty - you cannot measure position and velocity perfectly well at the same time. General Relativity does not have this, but it does have black holes - a concept with doesn't map well into Quantum Mechanics when the size of the black hole becomes comparable to the size of the particle. Worse, attempts to model gravity as a force caused by the interchange of gravitons (the way that other forces are done in Quantum Mechanics) have not worked - the infinities are too bad to actually do any calculations.

None of this matters on most scales - in the LHC quantum particles don't care that the spacetime is gently curved, and in the solar system or galaxy the spacetime doesn't care that there is quantum uncertainty at some very small microscopic level. But when the virtual particles get heavy enough that they affect the curvature of spacetime enough to create black holes, then things get nasty - there is not reason to expect that the "spacetime foam" on these small scales has a flat background spacetime , and so both theories are incomplete and break down.

Re:A decade long project

[Xenophon Fenderson,]

Thank you both for your responses!

Monster Strikes Again

[sexconker]

So the $500 high-energy gamma-output cables I bought actually DON'T improve my ping?

FUCK YOU MONSTER CABLE!

Planck length

[PinkyDead]

Aaarrggghh!!!

Re:Planck length

[MagicM]

Is this a pirate joke?

If not, it should be.

Re:Planck length

[Akardam]

... the Planck length would be about as long as a tall cedar tree.

I prefer to measure my Plank lengths in redwood or pine, myself.

Oh, wait...

Re:Planck length

[ozbird]

Nitpick: Pirates go "Arr!"
"Aaarrggghh!!!" be the sound of a lubber walkin' the Planck.

Re:Planck length

[Anonymous Coward]

The size of the universe a lot more than simply its age, so it's not just ~15 10^9 light years but around 100 to 150 billion light years (yes, a difference of about an order of magnitude)...

http://en.wikipedia.org/wiki/Universe

Re:Planck length

[imakemusic]

They go "Aaarggghh!!!" when they come in contact with ninjas.

Re:Planck length

[Bob-taro]

If the nucleus of a single atom were expanded to the size of the known universe (15 billion light years across--itself an almost unimaginable distance), the Planck length would be about as long as a tall cedar tree.

The height of a cedar tree? You must be thinking of "plank" length.

Re:Planck length

[MagicM]

What do ninjas have to do with Plancks?

Re:Planck length

[amRadioHed]

What do you mean?

Re:Planck length

[PinkyDead]

"Aaarrggghh!" is the imperfect past participle of "Arr!".

It's all in "Spinkley's Continuing Pirate Grammarr!", if you cared to read it - or be ye just a land lubber, Arrgg?

Re:Planck length

[Man Eating Duck]

size of the known universe (15 billion light years across--itself an almost unimaginable distance)

Nitpicking: It's 93 billion light-years (radius 46.5 billion), see Misconceptions.
It doesn't really matter, as the distances involved are so mindbogglingly large that in most cases the only explanation you need will be: "So large that your mind can't cope with it". The same thing goes for the infinitesimal size of an atomic nucleus. An error of an order of magnitude still gets the point across :)

Re:Planck length

[Wargames]

Yet if it were infantessimally small Achilles could not outrun the tortoise. http://en.wikipedia.org/wiki/Zeno's_paradoxes

Re:Planck length

[Anonymous Coward]

Yarr, thou walk it only once, lad ...

Re:Planck length

[Cantus]

Uhm, the size of the universe is 93 billion light years, while the age of the universe is about 14 billion years. Not the same thing.

A better analogy would be:

If a single atom were expanded to the size of the observable universe, the Planck length would be about as long as a football field. (Thank you WolframAlpha.)

Einstein still being proved correct

[defyg3]

I'm seriously blown away by how great of a scientist this guy was. I mean, its 100 years later and he is STILL being proved correct. Imagine what we could do if we still had this guy around. Its just so amazing to me.

Re:Einstein still being proved correct

[im_thatoneguy]

Decades ago I observed that the sky was blue. People to this day people still find evidence I was correct as a child. I imagine in 1,000 years people will still be recognizing the correctness of my observations. I am like a God among men!

Re:Einstein still being proved correct

[Anonymous Coward]

"The sky is blue." Yeah, that's the same as Einstein's four amazingly insightful theories.

Re:Einstein still being proved correct

[BradleyAndersen]

Einstein was a fraud. Look around and see what he did after his marriage to his first wife (http://en.wikipedia.org/wiki/Mileva_Einstein) ended.

Re:Einstein still being proved correct

[JustNiz]

He gave her a house and money. wow what a bastard he was. NOT.

Obligatory Maxwell

[sexconker]

No - Einstein never killed a bitch.

Joan was quizzical - studied pataphycial science in the home. Late nights all alone with a test tube, oh, oh oh, oh.

Maxwell Edison (majoring in medicine) calls her on the phone.

"Can I take you out to the pictures, Jo-o-o-oan?"

But as she's getting ready to go, a knock comes on the door.

Bang bang Maxwell's silver hammer came down upon her head.

Bang bang Maxwell's silver hammer made sure that she was dead.

Obligatory analogy

[BForrester]

The summary *is* a bit skimpy on important details.

A - My brother and my parents, travelling in separate vehicles, arrived at my house at the same time.
B - Therefore, my brother's Ferrari and my parents' RV both travel at the same speed.

No logical gaps between A & B there. Move along.

Re:Obligatory analogy

[Anonymous Coward]

Better analogy (RTFA)

A - My brother and my parents left the same destination within 2 seconds of each other
B - They traveled along the same path without stopping to my house in different vehicles
C - They arrived at the same time
D - therefore they traveled at the same speed

Re:Obligatory analogy

[Anonymous Coward]

Are they driving the same route? Did your brother not ride with so he could burn down a j? Will he share?!?

Re:Obligatory analogy

[MillionthMonkey]

Didn't they stop at a diner along the way?

Re:Obligatory analogy

[Anonymous Coward]

yes, except I'm pretty sure this stated they started at the same location. So it would be closer to:

A - My brother and my parents, travelling in separate vehicles, arrived at my house at the same time.
B - Both left from my parents house within two seconds of each other.
C - I live >10 miles/16 kilometers away from my parents house
D - Both vehicles are limited to "reasonable" speeds for each (i.e., the ferrari probably cant exceed 120MPH, and the RV probably can't get over 70MPH)
E - Therefore, my brother's Ferrari and my parents' RV both travel at the same speed or at least within 10% of each other.

There, ftfy

Re:Obligatory analogy

[FailedTheTuringTest]

I think item B in your list is actually the thing that we're trying to test here. So more like:

A - My brother and my parents left the same destination within 2 seconds of each other
B - Because of the difference in suspension between the two vehicles, if there had been any potholes bigger than a certain size, one vehicle would have had to travel slower than the other
C - They arrived within 0.9 seconds of each other
D - Therefore there were no potholes bigger than the size mentioned above

(There might possibly be smaller potholes, too small to affect either of the vehicles in this test. You could repeat the experiment with a bicycle, a skateboard, and one of those roller wheels you use to trace distances on a map.)

Re:Obligatory analogy

[LordLimecat]

Except that youre relying on the fact that they arrived at the same time to infer that they came from the same place, and using that inference to validate their travelspeed. Thats called circular reasoning.

Re:Obligatory analogy

[jimmydevice]

The brother JUST THOUGHT it took longer. And No, he's a bogart.

Enough is enough

[oldhack]

This Einstein guy is starting to really piss me off. Someone gotta take him down a notch or two.

Re:Enough is enough

[Tiger4]

Regression to the Mean is always in effect. Though sometimes it is enforced by Agression of the Meanest.

Re:Slow news day.

[tekrat]

Particle man, Particle man,
Doin' the things a particle can.
What it's like, it's not important, Particle man.
Is he a dot, or is he a speck?
When he's underwater, does he get wet?
Or does the water get him instead?
Nobody knows. Particle man.

Re:Slow news day.

[AP31R0N]

Worse yet, they changed the outcome of the race by measuring it.

i lost 300 big boys on that!

No one knows more than the average slashdotter

[John Hasler]

Of course, most of what he knows isn't true...

Obligatory

[ub3r n3u7r4l1st]

I, for one, welcome our new race of Einsteinian intergalactic overlords!

Mass, gravity, and the speed of light

[wowbagger]

OK, here's one for the physicists in the audience (and pardon the simplification of terms here, but...)

1) Being deeper in a gravity well slows time relative to being further out.
2) All things which have mass have gravity wells.
3) Photons have mass (NOTE TO THE CLUELESS: "mass" and "rest mass" are two different things - photons have no rest mass, but they most certainly have relativistic mass).
4) By 2 and 3 photons should have a (small) gravity well. More massive photons (higher energy and thus shorter wavelength) have deeper wells.

Thus, wouldn't 1 and 4 lead to higher energy photons "clocks running slower" (since they are deeper in a gravity well) and thus propagating as a lower speed as viewed by an observer outside their gravity well - and that effect would be negligible for all but the most massive photons.

(for the physicists: feel free to expand and clarify on the oversimplifications I've made here. This is, after all, targeting a Slashdot audience which has rather a wide spread of backgrounds).

Re:Mass, gravity, and the speed of light

[mea37]

"Thus, wouldn't 1 and 4 lead to higher energy photons 'clocks running slower'"

It's been too long since I've really looked at relativity for me to agree or disagree with this bit, but let's assume you're right...

" thus propagating as a lower speed as viewed by an observer outside their gravity well "

I think not. Your clock has nothing to do with how fast I see you moving. That's why it's your clock and not mine.

Re:Mass, gravity, and the speed of light

[Anonymous Coward]

Considering that speed of gravity equals speed of light, I guess it's more like a gravity cone..

Re:Mass, gravity, and the speed of light

[camperdave]

My armchair understanding of it would be: if their clocks are running slower, they would appear as a lower frequency photon. They would still propogate at the same speed.

Re:Mass, gravity, and the speed of light

[Tyler Durden]

Anything that moves at the speed of light does not experience a passage of time and has no "internal clock" to speak of.

This is how people figured out that neutrinos had a rest mass when at first the Standard Model assumed that they didn't. It was discovered that neutrinos could oscillate between different lepton flavors. But for that to happen they would have to experience the passage of time. And since particles without a rest mass always travel at the speed of light, they had to have mass.

Re:Mass, gravity, and the speed of light

[ChangelingJane]

Yummy! I'll have sprinkles on mine, please.

Re:Mass, gravity, and the speed of light

[Anonymous Coward]

Photons do not have mass. "Relativistic mass" is a terrible term and I hate it. You have to look at the relativistic equations to understand where it comes from. You can express the total relativistic energy, in short, as E=sqrt((pc)^2+(mc^2)^2). For a particle without mass, such as a proton, this reduces to E=pc. However someone figured out that for a particle with mass, you can represent the energy as E=gamma*mc^2, which is Einstein's famous equation with a factor dependent on the speed of the particle.

So someone figured that if you find the energy using the original equation, then equate it to the second way of writing it, you can kind of take that second "m" to be a "relativistic mass" of sorts, and apply it to any kind of particle, even massless ones. But it isn't actually "mass" in the true sense of the word. In reality saying something has "relativistic mass" is more like saying that total energy of the particle, while in motion, is the same as if the particle was not moving at all but just got more massive.

While that might be a fun mental exercise to undergo, it isn't a very useful thing from a theoretical standpoint.

So no, photons do not have gravity wells, as they do not have mass.

By the way, the reason photons are affected by gravity at all, according to Einstein, is that things with mass curves spacetime itself. The photons have to move through spacetime, so they curve with it.

Re:Mass, gravity, and the speed of light

[ceoyoyo]

The problem is, it's US measuring how fast the photon is going, with our clock, not the photon measuring with it's clock.

Besides, the photon is moving at the speed of light so it experiences no passage of time anyway.

Uncertainty rule?

[Anonymous Coward]

Didn't they already invalidate the results of the race by measuring it?

English is an imprecise language

[Anonymous Coward]

I read that as "Intergalactic Race" (beings, êtres) not "Intergalactic Race" (racing, course).

Language sometimes is TOO simple.

Re:English is an imprecise language

[pwfffff]

Yeah, same here. I had mixed feeling about receiving the first news of alien life from frickin' /.

more information

[bcrowell]

This is actually just the latest in a series of measurements of this type. Since the Nature paper isn't free online, people may want to look at this similar paper from earlier this year that is available.

The article talks about testing "some theories" of quantum gravity. AFAIK the only theory of quantum gravity that makes anything like a prediction that could be tested in this way is loop quantum gravity (LQG). The two leading contenders for a theory of quantum gravity are LQG and string theory. String theory essentially assumes a background of flat spacetime (plus an xtra 6 rolled-up dimensions), so I don't think it's capable of addressing the issue of whether spacetime is frothy at the Planck scale. LQG doesn't assume a background of flat spacetime, and in fact one of the main research programs in LQG is focused on showing that flat spacetime can emerge as a solution to LQG in the appropriate limit. LQG unambiguously predicts that the vacuum is dispersive, i.e., that the speed of light depends on the energy of the photon. However, LQG does not unambiguously predict the exact form of the energy-dependence. The possible form that is usually assumed in order to evaluate observational tests is |v/c-1|~(E/E_P)^n, where v is the speed of the photon, c is the speed of cause and effect in relativity (often referred to as the speed of light), E is the energy of the photon, E_P is the Planck energy, and n=1 or 2. Previous observations, such as the one in the arxiv paper I linked to above, have pretty much ruled out n=1, so if LQG is right, we'd presumably have to have n=2. Some people have been saying that LQG is ruled out by these measurements, but I don't think that's really correct, it's just constrained by them. Here is a paper by LQG researchers discussing the empirical tests, and they don't seem to be saying "OK, we give up." It's actually very exciting for people in quantum gravity to have observations that even have some chance of disproving a theory (or some version of a theory); the whole field is a dead end if it can never be tested by experiment.

In a broader sense, the holographic principle gives strong, model-independent reasons for believing that spacetime is probably discrete, not continuous, at the Planck scale. Otherwise it's hard to imagine how there could be an upper bound on the information content of a given region of space. And any theory in which spacetime is discrete at the Planck scale will naturally give a dispersive vacuum. Therefore I'd say that either (a) we should eventually observe dispersion of the vacuum once the observations get sensitive enough, or (b) the holographic principle is telling us something that we don't yet understand.

Two good popular-level books that get into this kind of thing are Three Roads to Quantum Gravity by Smolen, and The Black Hole War by Susskind. Because Smolen and Susskind represent very different points of view on quantum gravity, anything that both books agree on is probably correct.

Re:more information

[mbone]

A very good summary - thanks.

string theory

[astar]

Yah, but think of the poor string theorists. Here they spend 30 years working on it, and they stack the department hiring processes so they will not be criticized for never have created a testable conjecture. Now some data comes in and half their theories crash.

Re:string theory

[ceoyoyo]

Actually, the big contender here was quantum gravity, which is more or less a competitor to string theory.

Re:string theory

[astar]

thanks

http://en.wikipedia.org/wiki/Quantum_gravity

Re:Slow news day.

[johno.ie]

Your point is well made, but it was 7.8 billion years.

And the winner is...

[Anonymous Coward]

Horse race announcer: It's a quantum finish! And the winner is-(Man holds up a board with the winning horse on it)
Horse race announcer: Harry Trotter!
Professor Farnsworth: No fair! You changed the outcome by measuring it!

Dispersion

[sugarmotor]

I thought the speed of light does depend on the medium through which light travels.

  * http://en.wikipedia.org/wiki/Dispersion_(optics)
  * http://en.wikipedia.org/wiki/Prism_(optics)

What they measured is a bit surprising that way.

Stephan

Re:Dispersion

[John Hasler]

> I thought the speed of light does depend on the medium through which light
> travels.

It does when the medium is not a vacuum. This observation established an upper limit on the dispersion of the integalactic vacuum.

Re:Dispersion

[sugarmotor]

"This observation established an upper limit on the dispersion of the integalactic vacuum." ->
That is not how it is presented. It is presented as if it was known to be a vacuum. (Einstein would still have an easy way out otherwise)

Stephan

Re:Dispersion

[MillionthMonkey]

The 0.9 seconds thing could easily have happened near the explosion. There was wavelength-dependent scattering of gamma rays by elastic collisions with the massive number of neutrons that were suddenly created there. A neutron would absorb the gamma ray, and after some brief time reradiate it in some other direction to go back its ground state.

Planck length

[elrous0]

I heard a good analogy once explaining just how small the Planck length really is--and why it's so out of reach of any conceivable measurement we can even dream of:

If the nucleus of a single atom were expanded to the size of the known universe (15 billion light years across--itself an almost unimaginable distance), the Planck length would be about as long as a tall cedar tree.

Plausible

[symbolset]

It's plausible that these two photons left 0.1 seconds apart, and in their journey the distance between them expanded with the rest of the universe around them until at their arrival they were 0.9 light seconds apart. The event was observed to be 2.2 seconds long from our point of view but in local time at the event it took much less time (0.27 seconds). At least that's my understanding of 8.2 redshift.

Comment removed

[account_deleted]

Comment removed based on user account deletion

Re:Slow news day.

[pnewhook]

Actually I could argue that water itself isn't wet - it just makes things wet. This is because the definition of wet is 'to be covered or soaked with a liquid such as water'.

I missed it!

[homesnatch]

Man oh man.. I stepped out to use the bathroom and I missed it... I had been waiting 7.3 billion years for this.

Re:Slow news day.

[The_Wilschon]

One interesting thing that stood out is they used the assumption that the effect of quantum gravity would be proportional to the energy of the light; is this what the theories suggested or is this another case of science getting lost in the translation to newspapers?

As far as I understand from my colleagues who worked on this analysis (now departed for other groups/institutions), the theories of quantum gravity which predict a linear relationship between photon energy and propagation speed are the simplest to test. There are other theories, and they are worth testing too, and some of them would no doubt also be falsified by the Fermi data, but the analysis to do so is more difficult and more complicated, so nobody has done it yet.

String Theory Scale...

[Xin Jing]

In "The Elegant Universe" Brian Greene http://en.wikipedia.org/wiki/Brian_Greene made a similar analogy in regards to string theory: if an atom were expanded to the size of our solar system, an individual string would be the size of a tree.

However, He didn't specify what kind of tree.

Re:String Theory Scale...

[elrous0]

Google Books lead me to it the page in the book where he talks about this here.

Re:String Theory Scale...

[Xin Jing]

It look like we are both right:

From the NOVA 'The Elegant Universe' transcript:

"In fact, if an atom were enlarged to the size of the solar system, a string would only be as large as a tree!" http://www.scribd.com/doc/185276/NOVA-The-Elegant-Universe-Transcript, jump to page 26 or keyword search for "solar system".

I find this similarity and difference between the book and the video interesting. While Greene doesn't specifically reference the distance in the video as being measured in Planck Length, the concept of enlarging an atom on a cosmic scale and using a tree as the reference as to the size of a string is nearly the exact same example at that used in the book. It's clear the intent is the same since the string theory subject matter is the same. Does the measuring in this example start at the heliopause or the termination shock?

In think both expressions captures the essence of the distances involved, but when you take something as inherently tiny as an atom and enlarge it to the size of our solar system measured across the heliosphere to the termination shock, we're still talking about incredible vast distances, and this just an atom which we're unable to view with any clarity using scanning tunneling microscopes. The distance analogy might as well be expressed as "can we see an atom on Pluto from the Earth".

Having the expression be "if an atom were enlarged to the size of the universe" is incomprehensible. Yet perhaps it's matched to the insurmountable task that string theorists have before them to provide a testable prediction. By suggesting that an atom be expanded to the size of the universe and the observer is then required to look for a specific tree to mark a unit of measurement is again suggesting an equally impossible and untestable and unfathomable concept. Yet with the universe example, no one will ever have that opportunity to say, "yes, I can see that Planck Length example that Brian Greene used is correct. From where I sit in my chair here at the edge of the universe, my calibrated equipment can detect that tree" is absurd.

Again I reference a quote from 'The Elegant Universe' video, this one made by S. James Gates Jr. from the University of Maryland on page 14 of the transcript I linked above, "If String Theory fails to provide a testable prediction, then no one should believe it."

At one point you are left with something you can't ever verify - and that's where facts end and belief begins.

I thought intergalactic gas had more effect

[shoor]

I thought electromagnetic radiation of different frequencies traveled at different speeds through a medium (as opposed to a vacuum). In this case, the medium would be intergalactic gas, very thin, but there's 7 billion light years of it. How come that didn't spread things out? Is it because the frequencies involved are so high?

Re:I thought intergalactic gas had more effect

[mbone]

Is it because the frequencies involved are so high?

Yes. That's true even for visible light, much less gamma rays.

Was there ever a doubt?

[stakovahflow]

Was there ever a doubt that Einstein still rules. Just look at Isaac Newton, that "gravity" of his was made a law. Hooray, Science! *Just stating the obvious* -Stak

Time

[SnarfQuest]

The observed time between the events could represent a much wider differential thanm the .9 seconds. If the faster photon starts at the begining of the 'ka', and the slower one starts at the end of the 'boom', with the faster particle passing the slower one sometime during the 7.3 million years, then you have a possible difference of (0.9 + 2.2 + 0.9) = 4 seconds. What is the expected time differential expected if the speed is based on wavelength?

Original article

[TeethWhitener]

For those of us who have a subscription to Nature but not to NYT for whatever reason: Here's the original article.

Doubly Special Relativity

[tylersoze]

Here's one theory that posits the speed of light would vary depending on the energy scale. Basically the thinking is that the Planck length should also remain an invariant quantity regardless of the reference frame, so you modify the Lorentz transformation in such a way to make that work.

http://en.wikipedia.org/wiki/Doubly-special_relativity

Do you always praise yourself?

[Anonymous Coward]

1. Log in and post something you believe is impressive,

2. Log out then anonymously praise your previous post,

3. PROFIT!!! (As your original post is modded up...)

how far?

[Anonymous Coward]

How could ANYTHING get here from 7.3 billion light years without hitting something and being blocked along the way.....?

Re:how far?

[symbolset]

Space is not only really big, it's also mostly empty. That may be why they call it "space".

/Oh, and it takes a lot of mass to block gamma rays - a 1 cm thick lead panel will only block half of the photons.

Re:Slow news day.

[Anonymous Coward]

That explains why my nuts got wet in your mouth!

GRB have no known sources

[forand]

Just to be clear while there have been some correlations between super-nova and GRBs, they are not confirmed to be from any single source. None have occurred within our Galaxy during the modern era.

Are you sure about that?

[gbutler69]

Photons with different wavelengths carry more or less energy depending upon frequency. High-Frequency is Higher-Engergy. E=MC^2. So, Higher Energy Photons are affected greater by gravity. Are they not?

Re:Are you sure about that?

[John Hasler]

Higher Energy Photons are affected greater by gravity. Are they not?

No. The force of gravity on anything, including a photon, is precisely proportional to the inertial mass. See the equivalence principle .

lots of authors

[rgravina]

Funny... I sent the link to a friend who does GRB-related research, and she said "thanks, I already know about it though, I'm one of the authors" :). Apparently there are 210 authors on that paper though. Imagine coordinating that.

Anyway, I don't know a thing about astrophysics so that's about all I can contribute to this discussion.

Woops!

[gbutler69]

Guess I should shut the fuck up about something that is not my area of expertise! Sorry about that!

Re:Woops!

[bingoathome]

No no no - Imagine if every body did that - a near empty /.

Leafy green

[Anonymous Coward]

All right, break out the lettuce!

Oops, wrong Einstein

This article seems a bit hyped (Re:i'm confused)

[ErkDemon]

A detector on NASA’s Fermi Gamma-Ray Space Telescope confirmed Einstein’s proclamation in his 1905 theory of relativity that the speed of light is constant and independent of its color, energy, direction or how you yourself are moving.

No, not really.

• The speed of light isn't supposed to be globally constant (now that we've moved on from special relativity to general relativity), only //locally// constant. If it was globally constant, it'd be difficult for gravitational fields to exist. Lightspeed plus gravity equals variable lightspeed (although local observers may not be able to sense the local variations because gravity should make their own local clocks run differently by the same factor).
• The speed of light isn't independent of direction, either, when gravitational fields are involved. Gravitational gradients have a habit of making light-velocities asymmetrical (or, running the argument backwards, an asymmatricality in lightvelocities counts as evidence of a conventional gravitational field). The velocity of light leaving a GR1915 black hole, is, arguably, zero. The velocity of light entering a GR1915 black hole is, arguably, greater than the background speed of light. The //average// speed of light (round trip) reduces in a region, as seen by outside observers, when gravity there is stronger (Shapiro effect). But if you're dealing with speed and direction, you're really starting to deal with velocities, and the rules for one-way light-velocities when gravity or matter are involved are a little different to those of SR.
• The speed of light also isn't isotropic when there's moving matter present. A moving gas-cloud should make the externally-measured speed of light greater in the direction of the cloud's motion than the other way. Fizeau verified this effect back in ~1850 with flowing water.
• The speed of light isn't unaffected by the observer's motion if the observer is accelerating (accelerative frame-dragging, Einstein, ~1920).
• The speed of light is also affected locally by the observer's motion if the observer is made out of real particulate matter (as opposed to the ghostly "mathematical" observers assumed by SR). Back to the Fizeau effect - if you observe a supernova through your spaceship window, the relative motion of the window glass to the nova has already modified the speed of part of the signal path. And if the observer's "moving" location is associated with a persistent gravitational feature that's deemed to be significant (say, a planetary gravitational well), then the motion of that gravitational feature should be associated with gravitomagnetic dragging effects.
• The speed of light //should// vary with colour when there are geometrical features in the metric that are comparable in size to the wavelength of some of the light being used. It's a "fractal" argument, the short-wavelength light "sees" a longer distance because it has to ride over the lumps and bumps that the longer wavelength light rides over. That's why, when we had an experimental result a while back, whereby shorter-wavelength light from distant bodies appeared to reach us more slowly than longer-wavelength light, it wasn't a huge surprise, because that's what we'd expect if the vacuum of space isn't perfect vacuum, or if there's quantum foam at extremely small scales (or if the higher-energy light is //so// high-energy that it's associated with virtual pair-production effects that create its own local particle-churning "medium".

So the original article's way of trying to screw an "Einstein Proved Right! / Einstein Proved Wrong!" headline from the experiment was icky. The journalist actually got some good, reasonable quotes from guys like Smolin, so they seem to have done their homework for the piece. The person who comes out of this badly is the principal investigator, who gave that stinky "Einstein proved right" quote to the journalist, k

Intergalactic Race?

[alexo]

And here I was, all ready to welcome our new overlords...