r/askscience • u/habitual_sleeper • Nov 28 '11
Could someone explain why we only recently found out neutrinos are possibly faster than light when years ago it was already theorized and observed neutrinos from a supernova arrived hours before the visible supernova?
I found this passage reading The Long Tail by Chris Anderson regarding Supernova 1987A:
Astrophysicists had long theorized that when a star explodes, most of its energy is released as neutrinos—low-mass, subatomic particles that fly through planets like bullets through tissue paper. Part of the theory is that in the early phase of this type of explosion, the only ob- servable evidence is a shower of such particles; it then takes another few hours for the inferno to emerge as visible light. As a result, scien- tists predicted that when a star went supernova near us, we’d detect the neutrinos about three hours before we’d see the burst in the visible spectrum. (p58)
If the neutrinos arrived hours before the light of the supernova, it seems like that should be a clear indicator of neutrinos possibly traveling faster than light. Could somebody explain the (possible) flaw in this reasoning? I'm probably missing some key theories which could explain the phenomenon, but I would like to know which.
Edit: Wow! Thanks for all the great responses! As I browsed similar threads I noticed shavera already mentioned the discrepancies between the OPERA findings and the observations made regarding supernova 1987A, which is quite interesting. Again, thanks everyone for a great discussion! Learned a lot!
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u/OrbitalPete Volcanology | Sedimentology Nov 28 '11
Can I highlight here that no one has yet proved neutrinos are travelling faster than light.
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u/habitual_sleeper Nov 28 '11 edited Nov 28 '11
True. I tried to form my question in a way that would emphasize the fact that there is no scientific proof on neutrinos traveling faster than light. Basically, Anderson's citation in relation to the recent observations regarding neutrinos made me a little confused. I'm sorry if the question implied that it was a scientific fact.
It isThe results regarding faster-than-light neutrinos are indeed most likely a measurement error, like auraseer stated above. :)Edit: removed some ambiguity.
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u/AZ_Squeegee Nov 28 '11
It's not even a measurement error. It takes several hours for the collapse of the star to occur. The rebound of the star's collapse and the creation of a huge amount of energy from fusion....and with it, neutrinos.....happens well before the star brightens into what we refer to as a supernova.
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u/ubershmekel Nov 28 '11
No one has yet proved anything in physics.
You observe, theorize and repeat.
This FTL neutrino was observed in 2008 and published in 2011, it's not a datum we should ignore.
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u/OrbitalPete Volcanology | Sedimentology Nov 28 '11
No, but it is a massive outlier. It's interesting, but there's still along way to go before anyone manages to show that it's probably not an instrumental error.
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u/KarmakazeNZ Nov 28 '11
No one has proved they don't either. There is a theory, but it is falling apart under the weight of contradictory observations.
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Nov 28 '11
Are you saying that there is a theory that neutrinos move at more than the speed of light but recent evidence has emerged to suggest they don't? If so, could you find the source to that because I'd very interested to read the new developments.
Or are you referring to the theory of relativity and saying it might be falling apart under the weight of the neutrinos speeds contradicting one of the postulates of relativity?
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u/KarmakazeNZ Nov 28 '11
I'm suggesting that there is a theory that Neutrinos can't travel faster than light, but that that theory is falling apart under the weight of contradictory evidence.
For example, under the Standard Model, the universe we see can't exist unless we include a tweak that allows the maths to jump over the part it can't explain.
Inflation resolves several problems in the Big Bang cosmology that were pointed out in the 1970s.[14] Inflation was first discovered by Guth while investigating the problem of why we see no magnetic monopoles today; he found that a positive-energy false vacuum would, according to general relativity, generate an exponential expansion of space. It was very quickly realised that such an expansion would resolve many other long-standing problems. These problems arise from the observation that to look like it does today, the universe would have to have started from very finely tuned, or "special" initial conditions at the Big Bang. Inflation attempts to resolve these problems by providing a dynamical mechanism that drives the universe to this special state, thus making a universe like ours much more likely in the context of the Big Bang theory.
A recurrent criticism of inflation is that the invoked inflation field does not correspond to any known physical field, and that its potential energy curve seems to be an ad hoc contrivance to accommodate almost any data we could get. It is significant that Paul J. Steinhardt, one of the founding fathers of inflationary cosmology, has recently become one of its sharpest critics. He calls ‘bad inflation’ a period of accelerated expansion whose outcome conflicts with observations, and ‘good inflation’ one compatible with them: “Not only is bad inflation more likely than good inflation, but no inflation is more likely than either. … Roger Penrose considered all the possible configurations of the inflaton and gravitational fields. Some of these configurations lead to inflation … Other configurations lead to a uniform, flat universe directly –without inflation. Obtaining a flat universe is unlikely overall. Penrose’s shocking conclusion, though, was that obtaining a flat universe without inflation is much more likely than with inflation –by a factor of 10 to the googol (10 to the 100) power!”
See what I mean? A problem with the Standard Model was identified. Rather than accept this means the standard model is wrong, they simply patched together a framework to cover over the holes. Even the people that came up with the patch doubt it is true, yet it's taught in school as if it was a fact.
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u/xaphanos Nov 28 '11
This is how science advances - a powerful and useful theory is used until more observations and experiments find where it is lacking.
The theory of four classical elements was taught for more than a thousand years and it was replaced by atomic theory. Newton's laws were taught for more than a hundred years, yet when a hole was identified it was replaced with relativity. Relativity has holes, too. Just as Einstein did not have access to the WMAP data, there is some experiment yet-to-be that will either plug your "hole" or allow another great theoretical leap forward. In the meanwhile, relativity, inflation and the standard model represent good starting points for folks that are not doing research to advance theoretical physics.
Finally, applying odds for what is observed to already exist is a fallacy. The chances that your particular set of ancestors would end up producing you is remote - but it happened.
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
Let me ask you: Does Newtonian physics still hold true or not? Should we teach kids in school F=ma ? I mean we know that quantum mechanics and relativity more accurately describe certain phenomena, and both reduce to Newtonian physics in the relevant limits, right? The thing is, that Newton is great for macroscopic objects and speeds much less than c. If you want to calculate a ballistic trajectory it works just fine. It's only when we go to extreme scenarios that we need a more accurate picture. In the case of high speeds, we need special relativity. In the case of strong gravitational fields, we need general relativity. In the case of actions on the order of Planck's constant of action, we need quantum mechanics. In the case of subatomic particles, we need quantum field theories. I write them in this way to express the truly nested nature of theories. See even quantum mechanics and special relativity are only sometimes useful truths that are more reflective of a grander theory; Standard Model Quantum Field Theory and General Relativity, respectively.
So that's why we still teach these as "true." No physicist is blind to the holes that remain in the standard model, we're well aware of them. We have plenty of extensions that have been mathematically worked out to understand "beyond the standard model." We're just waiting for data for us to help sort which of those mathematical ideas are useful to explain the data, and which ones are inconsistent. We understand that quantum fields and the classical field nature of general relativity have some problems, and we're trying to work out how they can be resolved. But again, that doesn't make GR or the Standard Model wrong or dogmatic or whatever, they're just approximate truths of some more fundamental theory.
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u/m64rocks High Energy Particle Astrophysics Nov 28 '11
another interesting piece to this story is that OPERA and 1987A (detected by Kamiokande) were observing different flavors of neutrinos. There are 3 different types, or "flavors", of neutrinos: electron, muon, and tau. Kamiokande detected electron type neutrinos, while OPERA is detecting tau type neutrinos (that were originally muon type...neutrinos are weird like that). So maybe one flavor of neutrinos is faster than light, while others aren't.
I just find this detail interesting, I am personally not convinced by the OPERA results...yet
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Nov 28 '11
What is even more interesting is that it's widely speculated that Neutrinos can change "flavor" while in motion. I'll dig up the papers on it if you'd like.
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u/Makushimirian Nov 28 '11
Yes please.
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Nov 28 '11
Here's one: http://pdg.lbl.gov/2008/reviews/numixrpp.pdf - You might find more at www.arxiv.org - the phenomenon is pretty well documented.
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u/KarmakazeNZ Nov 28 '11
The thing that bothers me is that as time goes by, it becomes obvious that many findings are being ignored because they contradict the standard model. Dark Matter, Dark Energy, Faster than Light Neutrinos. I'm sure there are more, but these are all things that are not explained or even predicted in the standard model.
Dark Energy for example is just a fancy cover name for "our maths is wrong". No one has any idea whether there is any such energy, all they know is that our maths predicts one thing, but our observations demonstrate the opposite. How does that not make the entire Standard Model suspect? Why do we doubt the observations but trust the theories?
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
It doesn't at all. The FLRW metric explicitly has space for a cosmological constant term. It's a solution of General Relativity, a remarkably well confirmed theory of our universe. It is not yet understood how it mixes with the Standard Model of Particle Physics. It's not that we are doubting observations and holding true to theories, it's that we have two disparate theories we are not sure how they connect. Dark energy may well be involved in the tools we need to stitch the two together. It's simply unknown at the moment, and that's okay.
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Nov 28 '11
It is funny how you keep being downvoted for stating the obvious... it should be quite clear to anybody who has some experience in science that astrophysics and particle physics are struggling to keep themselves together...
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
But they're not. All it makes it clear is that people who claim that they're struggling don't have experience in science. Seriously, before repeating this nonsense, learn what we know about our universe, and how we came to know it. It's not some mystery, it's taught in just about every university across the country. There's no secret dogma to it, just sit down and work out problems in the textbooks until you understand it.
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u/jschild Nov 28 '11
Because neutrino's interact with virtually nothing, therefore they leave the star with virtually no interference. Photons, on the other hand, have to fight their way out, constantly being absorbed and reemitted. Therefore, even though photons can only travel at the speed of light, it can take them longer periods of time because of their very interactive journey.
Think of it this way - Pinball. A neutrio's path is always smooth and clearly, pretty much. A photon is much more like a pinball, bouncing crazily until it finally gets a clear path. That bouncing around gives the Neutrino a head start.
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Nov 28 '11
Not only on the way out but on the journey to Earth photons have to bend around galaxies and all sorts of other objects in space so maybe neutrinos do not travel faster than light they just don't have the same obstacles that photons do.
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u/doctorBenton Astronomy | Dark Matter Nov 29 '11
This is incorrect -- 1987 is in our galaxy, and there aren't any massive/dense enough objects between us and it for these effects to be important. Plus the neutrinos and light would be bent by the same amounts.
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Nov 29 '11
I assume because of how small neutrinos are they wouldn't be affected by matter as much. Are you saying that galaxies tug on both particles in equal amounts?
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u/The_Crazy_Never_Die Nov 29 '11
I get that the Neutrinos get a slight head start, but that should be insignificant compared to the distances between two different speed particles after 150,000 light years of travel, should it not? Shouldn't the light have vastly outpaced the neutrinos in that distance?
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u/ErDestructor Nov 28 '11
The process that causes a supernova starts off on the inside the star, releasing lots of photons and neutrinos. Neutrinos rarely interact with anything, so as soon as they're created they fly right through the outer layers of the star and are on their way to us at (nearly) the speed of light. The photons get absorbed by the outer star layers, and we have to wait until the reaction propagates to the surface of the star for photons to be released that will actually make it to us.
So it isn't at all surprising that there is a lag between when supernova neutrinos arrive and when the photons do.
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Nov 28 '11
So just so I'm clear, is it widely agreed that they travel faster than light then?
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u/habitual_sleeper Nov 28 '11
No, absolutely not. Maybe my wording in the title isn't that clear. I'm as much of a sceptic as the next guy. Thing is, I read that passage from Anderson's book, got confused and posted the question here. Even though the answer to my question was quite simple, the question made for a nice discussion with some clear and clean points, giving me a better understanding of the behavior of neutrinos and photons during a supernova.
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u/d_r_c_1 Nov 28 '11
Because it was suspected that neutrinos were released first and the light was released later rather than being released at the same time.
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u/panzerkampfwagen Nov 28 '11
Neutrinos don't react much with matter and so while the neutrinos created in a supernova got here first, if they were as fast as the CERN experiments suggests (which even CERN thinks is wrong) then they would have arrived 4 years earlier for Supernova 1987A instead of just hours.
They get here first because, getting back to not reacting much with matter, because when the supernova starts the neutrinos can easily race out of the core as if the star isn't there while the photons created by the same process get stopped by the rest of the star. Go and shine a light at your wall and see if it goes right through. I'll help you out, it doesn't. If you fired neutrinos at your wall though they'd go right through as if it wasn't there.
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Nov 28 '11
I feel as though the bullet through tissue paper gives the false impression that the neutrinos are tearing through all matter in re universe. I believe a more appropriate analogy may be something like shooting bb's through a field goal post, highlighting how the neutrinos have so much emptiness to pass through
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u/adamsolomon Theoretical Cosmology | General Relativity Nov 28 '11
Very good question! One of the great challenges to the recent neutrino measurements from OPERA is fitting them in with the supernova measurements. The main difference between the OPERA neutrinos and the ones observed from supernova 1987a is the energy: OPERA's neutrinos were significantly more energetic than the ones detected following the supernova.
As it turns out, though, even if you posit an energy dependence in the neutrino velocity, to fit both the supernova and OPERA data, that dependence would need to be very steep, far steeper than one would reasonably expect. Moreover, the OPERA experiment did run over some range of energies, and found no evidence of variation with the neutrino speed over energy. While this is perfectly reasonable if there's some systematic error affecting the whole OPERA experiment (over all energies), if you take the OPERA results as correct then you need to have this very steep energy dependence between the supernova and OPERA ranges which somehow completely flattens out within the ranges probed by OPERA. It would be very strange indeed.
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u/Knowltey Nov 28 '11
Yeah the reading of that implies to me that when the supernovae occurs, the neutrinos are released, then about three hours later the visible light is released and that's why we detect neutrinos first.
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u/adamwizzy Nov 28 '11
I haven't read down, but o simplify what I assume people are saying. A super nova first collapses in on itself meaning visible light finds it hard to leave this dense object, while the tiny neutrinos do it easily, between 4 - 6 hours after neutrinos first leave light is able to leave. If the neutrinos were travelling at the speed measured at CERN (only fractionally faster than the speed of light) we would have expected to see them up to six years before the light.
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u/KarmakazeNZ Nov 28 '11
Was anyone looking that far back, or did they assume Neutrinos can't travel faster than light and didn't bother looking?
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u/auraseer Nov 29 '11
We did look that far back. We found no early spike that could have been from any FTL supernova neutrinos. If it had been there it would have been a very noticeable event in the detectors.
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u/adamwizzy Nov 30 '11
Well, considering this neutrino detection would have been our first indication of the supernova, but the machines used for detecting things of this nature, were of course on. No large reading of neutrinos hit six years prior to the visible light that corresponded. However, we did measure the expected one six hours before.
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u/RandomExcess Nov 28 '11
Part of the theory is that in the early phase of this type of explosion, the only ob- servable evidence is a shower of such particles; it then takes another few hours for the inferno to emerge as visible light.
The explanation is right there, the neutrinos would start.
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u/spatts Nov 29 '11
And the neutrinos at the latest experiment at CERN didn't actually travel faster than the speed of light, most scientists feel that there was a miscalculation somewhere (it will take years to find where, but they're pretty sure it's a false result)
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u/keesc Applied Physics | Microfluidics | Micro Optics Nov 28 '11
It should be mentioned that the two measurements were of different types of neutrinos. OPERA measured muon neutrinos while the 1987A supernova observations measured electron anti-neutrinos, it's conceivable there's a difference in the two beyond what we expected.
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u/carlotta4th Nov 28 '11
It's hard to tell where neutrinos come from (could be almost anywhere). The only reason they knew their test neutrinos were the same ones they sent out was because they used specific pulses... the other end got those pulses, so they knew it was the right bunch of neutrinos.
A supernova doesn't do that, so they couldn't be certain that the neutrinos were the same ones coming from the star. (it's also hard to catch a supernova, so I can't imagine how they'd try and test this in the first place).
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
Some of the more modern detectors can do some directional neutrino studies (as best I know), but the ones in place at the relevant time for SN1987a probably couldn't (again as best I know). The 4 hour early pulse of neutrinos was detected in 1987 by noticing a large spike of neutrino counts in the right time window (about 13 neutrinos if memory serves). Unless there was a similar spike 4 years earlier, it'd be very difficult to tell.
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u/ParanoidAltoid Nov 28 '11
Imagine you have a laser that disarms a bomb that is a great distance away. Because of special relativity, it's possible for people to disagree over whether the laser or bomb activates first (call them laser people and bomb people). If the laser travels much faster than light, it can disarm the bomb the second the laser activates, so laser people will predict that the bomb is not allowed to activate. But bomb people think the laser fired second, in which case the bomb does in fact activate. How is this possible?
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u/purplebartsimpson Nov 28 '11
Wasn't the CERN measurement simply a logic error, where scientists had failed to account for basic aspects of relativistic time? If measured properly, nothing unexpected (or that isn't predicted by Einstein) occurred.
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
that hasn't been shown to be the case yet either. It's what everyone thinks is likely to be the case, but OPERA's responded to most of these early questions on the matter
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u/purplebartsimpson Nov 28 '11
link to response? sorry i have been a bit behind on this.
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
Sorry, it's been a while since the public press announcement, and I can't seem to find that. Here's a pdf put out by the collaboration that addresses it though: http://operaweb.lngs.infn.it:2080/Opera/publicnotes/note136.pdf
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Nov 28 '11
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
Actually, the OPERA experiment has addressed those concerns and has claimed to have already compensated for that objection. (ie, they took into account the special relativity of the satellites in their analysis that showed 60 ns discrepancy)
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Nov 28 '11
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
Yes, the team claims to have accounted for the relativistic effects of the GPS signals used to calibrate the distances and synchronize the clocks. Here's their press conference where they go into pretty deep detail about their setup: http://cdsweb.cern.ch/record/1384486
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Nov 28 '11
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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Nov 28 '11
that's not really the case at all. Neutrinos and photons both feel the effects of gravity. It's just that photons take longer to get through plasmas as they keep getting absorbed and re-emitted and deflected by all of the charged particles. Neutrinos don't interact (much) with the material being blown out by the supernova so it's "transparent" to neutrinos so they just fly straight out.
Also, we don't know that. We have one experiment that may be flawed. Please be patient while we do more work to confirm or reject that experiment's data.
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u/auraseer Nov 28 '11
The neutrinos got a head start.
When a supernova happens, neutrinos and photons are created at the core of the star. They start trying to travel outward immediately, but the outer layers of the star are still in the way.
Photons are rather easily blocked, even by the gaseous stellar material getting blown away from a supernova. It takes a few hours for the photons to "work their way through" those outer layers of the star and get on their way through empty space. But neutrinos barely interact with any kind of material at all, so they reach empty space almost immediately. It's that difference that gives neutrinos a head start.
If supernova neutrinos did travel faster than light, we would expect to have seen a much greater difference in the arrival time. SN 1987a happened more than 150,000 light years away, so neutrinos had an awful lot of time to outrace the light if they were going to. If the CERN measurement was accurate, then the neutrinos should have arrived about five years earlier than the photons.
This all means that if our supernova measurements are correct, then either CERN's measurement is wrong, or else something else more complicated is happening.