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On 9/8/2018 at 8:09 AM, HansonKerman said:

How fast does a neutrino move?

This is actually one of the big current questions in particle physics! The honest answer is no one knows for sure. What we do know is that they move unmeasurably close to the speed of light, but they also have oscillations in what kind of neutrino they are which suggests they experience time. From relativity we expect that if you travel at fully the speed of light you don't experience time, so the common answer is that they probably travel very very close to the speed of light.

[SillySarcasm] Unless your measuring equipment has loose cables, then they can travel even faster than light! [/SillySarcasm] http://www.sciencemag.org/news/2012/06/once-again-physicists-debunk-faster-light-neutrinos

I'll try to find the relevant articles and edit them in later today, but one of the most striking pieces of evidence we have that they travel immeasurably close to the speed of light is a simultaneous signal we got of neutrinos and high energy photons called gamma rays reaching earth at the same time from an extremely short lived and distant event called a blazar. In a race of even immeasurable distance, it seems that neither light nor neutrinos have a serious edge! The experience of time was originally called the Solar Neutrino Problem, and I believe was solved by.... Super K. in Japan? I'll need to look it up and edit it in later! Edit: Super K. was the first, and SNO confirmed it.

Edit: Found a bunch of the original papers about the findings, but (to my surprise) nothing generally consumable that would be useful to paste in. I really thought I would!

Edited by Cunjo Carl
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1 hour ago, K^2 said:

Almost certainly not.

When you will make an experiment where certainly not, these words will mean.
Or a stopped neutrino.
Until then - any difference is below accuracy. :D And sometimes faster.

Edited by kerbiloid
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So many beautiful theories were crushed under weight of reality...

P.S.
Distance = 1.000 ly.
Flight time of neutrino?

P.P.S.
Before judging someone's understanding, do you at least realize the difference between "=" and "" ?

Edited by kerbiloid
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18 minutes ago, kerbiloid said:

Distance = 1.000 ly.
Flight time of neutrino?

Distance 100km. Flight time of an aircraft? I'll let you figure out what the critical bit of information you're missing relevant to an elementary particle.

Luminal speed has implications. It says, explicitly, that worldline is on a light cone. And that means that the particle is either massless or off the shell. Since a free particle has to be on-shell, and neutrinos exhibit behavior inconsistent with massless particles, clearly 'lightspeed' is always wrong. But you can't even claim an approximation. Everything we know about physics says that walking-pace neutrinos aren't just possible, they're all around us. It's another matter that we can only detect neutrinos possessing enough energy to trip a sensor. So a detectable neutrino travels very close to light speed. Saying that all neutrinos travel at lightspeed, even if you just forgot to use the word "nearly" in there, is flat wrong.

And I'm well aware of the difference between identity (тождество) and equality (равенство). I'm also well aware that neither of these imply an approximation, so either you need to brush up on these yourself, or I have no idea where you're going with these.

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3 hours ago, K^2 said:

Distance 100km. Flight time of an aircraft?

A plane speed may vary from 150 to 2000 km/h.
Have neutrinos moving at 0.1c speed already been registered?
Have 0.999c ones been?

So, without sci-looking blah-blah the answer is just 1 ly / 1 c.
If there are 0.999999999999999998c and 0.999999999999999999c fast neutrinos, today you anyway can't measure the difference, so a practically reasonable answer is "1 year"..

Also don't just forget to use the word "nearly" with any physical value by default.
In your first year in a college they will explain this to you (see Metrology).

3 hours ago, K^2 said:

<snip> blah-blah and my bio

The question was: "how fast".
I gave a brief answer: Lightspeed.
Cunjo Carl gave an excellent detailed answer discovering the real nature of things.
If you were late to answer, feel free to bring more info.

 

Edited by kerbiloid
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39 minutes ago, kerbiloid said:

Have neutrinos moving at 0.1c speed already been registered?

You could try reading the paragraph above. No neutrino has ever been registered directly, period. Their very existence is inference on indirect measurements. Indirect measurements say walking pace neutrinos exist. So yes, you are still absolutely wrong when you say neutrinos travel at (nearly) lightspeed.

And maybe they teach you not to use the words like "nearly" and "exactly" when talking about physical quantities at the same institution that taught you not to write clean code for a short demo. If you ever actually had taken even a survey course in physics or mathematics from a reputable university, they would teach you better. The fact that you are completely wrong regardless of this is an excellent indication of why nuances are important. You can't divide a real number by zero, but you can divide by nearly zero all day long. And if you don't think that's important, I would recommend a career in arts, far away from anything where precision actually matters.

Again, I'd let it slide if you were simply wrong on the basis of missing that "nearly", but the fact that you're still under a miraculous impression that your claim was right after being told by somebody who studied particle physics for nearly a decade that it's not even remotely close, is the exact reason why its actually critical in highlighting your ignorance of the subject.

You systematically replace facts by fiction, and if you simply answered questions outside of your competence, which is common enough on this forum, that wouldn't be a problem. The problem is that when you are given the exact reason why it is wrong, you don't even understand enough to get the explanation. And rather than say, "well, I don't understand that," you double down on your misinformation and pretend that anything you don't understand does not exist. I'm surprised, you acknowledge existence of subatomic particles at all, at this rate.

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2 hours ago, K^2 said:

You could try reading the paragraph above. No neutrino has ever been registered directly, period. Their very existence is inference on indirect measurements. Indirect measurements say walking pace neutrinos exist. So yes, you are still absolutely wrong when you say neutrinos travel at (nearly) lightspeed.

https://en.wikipedia.org/wiki/Neutrino#Speed

They still are trying to measure the difference. 

2 hours ago, K^2 said:

taught you not to write clean code for a short demo

Yeah, I remember that thread where you were trying to show up with your olympic achievements thinking that creating/deleting a local object in a loop differs from creating/deleteing the same local object in a function to be made and called from that loop.
As well as not even understancding that it takes less type conversions to make (int) once in the "for", rather than do (unsigned int) or (uint64) on every loop pass.

That was funny, but you are wrong (as almost always): that was not a sample of code. That was a calculation result with its source in case if anyone wants to make it better.

2 hours ago, K^2 said:

You can't divide a real number by zero

In the first year they'll explain L'Hospital rule also. Usually you don't need to divide something by zero.
Also you should be very careful with real number arithmetics at all, and always use a precision value (like I do).

2 hours ago, K^2 said:

And if you don't think that's important, I would recommend a career in arts, far away from anything where precision actually matters.

In arts I'm even much worse, so no.

2 hours ago, K^2 said:

Again, I'd let it slide if you were simply wrong on the basis of missing that "nearly", but the fact that you're still under a miraculous impression that your claim was right after being told by somebody who studied particle physics for nearly a decade that it's not even remotely close, is the exact reason why its actually critical in highlighting your ignorance of the subject.

You systematically replace facts by fiction, and if you simply answered questions outside of your competence, which is common enough on this forum, that wouldn't be a problem. The problem is that when you are given the exact reason why it is wrong, you don't even understand enough to get the explanation. And rather than say, "well, I don't understand that," you double down on your misinformation and pretend that anything you don't understand does not exist. I'm surprised, you acknowledge existence of subatomic particles at all, at this rate.

Let's see. All this waterfall has been caused by just one word: "lightspeed" (and btw it's a quote).

Not to insult one's profile, but your "Brain" avatar tells me much more about you than my silly answers tell you about me.

Nice to have such loyal fans ready to follow every my post, but maybe Brain just lacks Pinkies irl.

 

Edited by kerbiloid
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I am not a physicist, but i find tone and explanations wanting until now, except @Cunjo Carl of course.

In an attempt to solve the problem, as a computer gaming archaeologist i see it that way that all neutrinos until now that were experimentally caught were traveling immeasurably close to c. But it is also clear that they have a small rest mass, so traveling at exactly c is theoretically not possible. But it is theoretically possible that they could travel at any speed, including hanging right in front of my nose and doing the Old Biff "McFly ... ?" :-)

It is only, practically that hasn't been detected in any experiment (the hanging part as well the Old Biff part) and nobody knows how to accomplish this. And what counts in physics is the experiment.

Right ? Right. Or not ? :-)

 

Edited by Green Baron
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My vision:
Neutrino velocity may or may not be the same as "lightspeed".
(It shocks me that a lepton can move at c, it should be slower).
But in math there are "=" (is equal), "" (is nearly equal), and "" (same as).

So, as far as it can be measured in known experiments, neutrino speed is "" c, and any measured difference is below accuracy limit.
Which means that there is currently no experimental evidence if it is "=" "equal" or "" "same as" or not, and any guessing about it is a theoretical speculation based on a used world model.

So, for "practical" (if this word can relate to neutrinos, lol) use, say for flight time, it can be considered as "=" "equal" (having in mind any reasonable result precision).

The question "how fast" can mean both "brief and rough" and "detailed and exact" answers.
I gave the former, Cunjo Carl gave the latter.

Is it "" (same as) or "=" (equal), can be known only since some experiment will give a result measurably differing from "1.0 +/- 0.00001".

P.S.
And btw how fast is photon? Lightspeed is a math abstraction (so ideally precise), photon is a physical particle (so by definition fuzzy).

Edited by kerbiloid
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1 hour ago, kerbiloid said:

https://en.wikipedia.org/wiki/Neutrino#Speed

They still are trying to measure the difference. 

Yes, because that would be direct confirmation of zero mass. Something physicists really like to have. Nonetheless, flavor oscillation is impossible under standard model if they are massless. And if they have a mass, they can travel at absolutely any speed. If you are not convinced by this argument, you should be arguing that neutrinos don't exist. We cannot measure them directly, just showers of particles they produce when they interact with matter. This is also why they have to be traveling at damn-near speed of light to be detected. Saying, "I believe they exist, but I don't believe they can travel at 10 miles per hour," is the kind of idiocy I generally expect from flat-earthers and creationists. They also like to selectively ignore the evidence.

1 hour ago, kerbiloid said:

Yeah, I remember that thread where you were trying to show up with your olympic achievements thinking that creating/deleting a local object in a loop differs from creating/deleteing the same local object in a function to be made and called from that loop.
As well as not even understancding that it takes less type conversions to make (int) once in the "for", rather than do (unsigned int) or (uint64) on every loop pass.

The fix I gave you avoided allocation all together, because std::vector::assign does not allocate if resize isn't required. I didn't realize that you remained clueless about that after I gave you the correct way to handle that loop. Moreover, assign itself will compile to a loop with just a few instructions and be inlined. There isn't an actual function call when you do std::vector::assign with an integral type. It's faster than memcpy.

I'm not even going to respond to the type portion, because you obviously never learned how to use a disassembler, if you still think STL sizes return ints on x64.

Please, please, just promise me you'll never come work in the Valley, and I'll leave your code alone.

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is this a "what is kerbiloid and how to struggle against it" thread?

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1 minute ago, K^2 said:

The fix I gave you avoided allocation all together, because std::vector::assign does not allocate if resize isn't required. I didn't realize that you remained clueless about that after I gave you the correct way to handle that loop. Moreover, assign itself will compile to a loop with just a few instructions and be inlined. There isn't an actual function call when you do std::vector::assign with an integral type. It's faster than memcpy.

I'm not even going to respond to the type portion, because you obviously never learned how to use a disassembler, if you still think STL sizes return ints on x64.

Please, please, just promise me you'll never come work in the Valley, and I'll leave your code alone.

Just believe me, I don't need advices from such "experts", I saw a lot of them.

 

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17 hours ago, Green Baron said:

[snip]

It is only, practically that hasn't been detected in any experiment (the hanging part as well the Old Biff part) and nobody knows how to accomplish this. And what counts in physics is the experiment.

Right ? Right. Or not ? :-)

I'm an experimentalist, so of course I say 'spot on!' :D

To quote a very nice recent paper on neutrino mass I just came across, we can rest assured that: "People are trying."
https://arxiv.org/pdf/1605.03159.pdf

What does a video game archeologist do? I'm actually really curious! I'm assuming it's more than trying to dig up copies of ET? ^_^

 

20 hours ago, kerbiloid said:

So many beautiful theories were crushed under weight of reality...

True. Too true... I'm still rooting for you though, de Broglie Bohm mechanics!

 

20 hours ago, kerbiloid said:

Distance = 1.000 ly.

Flight time of neutrino?

Assuming a 'prototypical' solar neutrino (300keV), and an approximation of the present best guess of neutrino mass based on cosmological experiments (50meV), the time of flight would be ~1yr + 500ns ! That's a fun thought experiment.

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4 hours ago, Cunjo Carl said:

Assuming a 'prototypical' solar neutrino (300keV), and an approximation of the present best guess of neutrino mass based on cosmological experiments (50meV), the time of flight would be ~1yr + 500ns ! That's a fun thought experiment.

How about 100 μeV neutrinos present in cosmic background radiation?

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6 hours ago, Cunjo Carl said:

What does a video game archeologist do? I'm actually really curious! I'm assuming it's more than trying to dig up copies of ET? ^_^

Idk. I don't play ET. I have studied prehistory (a subject of geoscience), but don't work in the field. And sometimes i play :-)

2 hours ago, K^2 said:

How about 100 μeV neutrinos present in cosmic background radiation?

"Almost certainly not" :sticktongue:

The paper sets the lower limit 3 magnitudes higher but states experiments are lacking.

https://www.katrin.kit.edu/

These guys plan to search between 10meV and 2eV.

 

btw.: Is it eV or eV/c² ? The latter, of course ... silly me.

Edited by Green Baron
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46 minutes ago, Green Baron said:

"Almost certainly not" :sticktongue:

The paper sets the lower limit 3 magnitudes higher but states experiments are lacking.

The post I quoted contains the 50 meV rest mass estimate. I don't claim to read absolutely everything, but I at least take time to read things I quote. The 100 μeV is the typical kinetic energy of background neutrons. That would put total energy at 50.1meV. This is standard notation, too. If you look at any literature on background neutrinos, you will see people talking about them being in 10-6 - 10-4 eV ranges. In general, when we talk about particles at non-relativistic velocities, kinetic energy is the value that's being quoted. Always. Including rest mass in energy is pointless when talking about things happening at small fractions of c. The electrons in a CRT are 5keV, not 516keV, because including 511keV in the energy is not useful. And neutrinos in question are 100 μeV.

Look, I've been doing particle physics for a living for a number of years. You're not going to catch me making dumb mistakes here.

But at least, you can tell the difference between meV and μeV. I do appreciate that.

P.S. dropping c² is pretty typical. Particle physics is usually done in "natural units", where c = 1 and ℏ = 1. It's a trivial matter to insert it back into results if ever we need the SI/cgs numbers. But otherwise, absolutely everything is measured in either eV or eV-1. Energy, mass, distances, and time.

Edited by K^2
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18 minutes ago, K^2 said:

But at least, you can tell the difference between meV and μeV. I do appreciate that.

And you're really having fun underestimating people and putting everyone down who doesn't feed your ego, is that so ? Because you make sloppy and marginally correct remarks to others, wait for a reply and then put them down in a personal way. Nice guy.

Breathe though the nose, relax, lean back, smile, think something positive like a successful return from Tylo. You're not the only educated person in the world, everybody has his/her specialties and here we can meet to discuss them.

Edited by Green Baron
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I don't expect people to be competent in everything. I expect people to understand limits of their competence. At least when they are demonstrated. Is that seriously too high of a bar for a sci & space subforum?

When I make a mistake and somebody points it out, my first response is to thank them for it. Because it makes me better, and it's these rare occasions for which I mostly visit this forum. If somebody else makes a mistake, I point it out just as I'd want it pointed out to me. If it's questioned, I provide an explanation. And I tend to have pretty good patience for it. I will write out pages-long detailed explanations, and I will break it down as far as I possibly can into understandable terms. But that patience is finite and does not apply to willful ignorance.

People who argue from nothing but ignorance, choosing to remain oblivious to their own incompetence do make me angry. And they should make you angry too. That kind of behavior reduces ability of others to learn something from a discussion. It is bad for absolutely all of us. It is not a behavior that should be protected.

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