7 ms·

The Case of the 5-Millisecond Cosmic Radio Burst (2014)

57 points by kposehn 12y ago

ghshephard 12y ago
re: " If the star is above that critical mass but spinning, the centrifugal force can help keep the star from collapsing right away" I still resent my Grade 11/12 physics teacher for insisting that there was no such thing as centrifugal force, and that what was really occurring was centripetal acceleration only. He basically decided that newtons third law would not exist in his classroom.
- pmalynin 12y ago
  He's not entirely wrong. The thing with centrifugal force is that by picking a different frame of reference, it completely disappears and the reason it arises is due to your frame of reference being different. Interestingly, however, is that it is possible to pick a frame of reference such that gravity disappears, so it too is a fictitious force in a way.
  - danbruc 12y ago
    Interestingly, however, is that it is possible to pick a frame of reference such that gravity disappears, so it too is a fictitious force in a way. I am not a physicist but that seems wrong to me or at least imprecise. You can select a frame of reference that makes gravitational forces disappear locally but there is no frame of reference that makes them go away globally.
    - jacquesm 12y ago
      That's the whole point of the exercise: to show that these frames of reference are all relative. And if you think about it, the exact point of origin of the 'big bang' might actually be a frame of reference relative to which gravity disappears globally. Relativity is a very tricky concept. Of course gravity is a 'real' force but the ability to shift your frame of reference is a powerful reminder that gravity and acceleration can look the same until you exit your frame of reference.
      - danbruc 12y ago
        I am not sure if I just misunderstand you, but we don't know if there was something like a singularity at the big bang and I would guess many doubt that there was. But if there was such a thing it was probably not at a specific point but everywhere. And you don't have to leave your frame of reference to see a difference between acceleration and gravity, they are distinguishable in any frame of reference.
        SixSigma 12y ago
        You're also talking as though the "big bang" is proven.
        danbruc 12y ago
        Depends on how narrow or broad you interpret the term. I would say back to the origin of the cosmic microwave background 380,000 years past the big bang the story is pretty well understood. Back to ten to the minus thirty two seconds the model still looks reasonable to me. The time before that makes me feel uneasy, inflation looks to ad hoc to me as a laymen. And I really don't believe there was some kind of singularity with infinite density at the very beginning, but I doubt many do. You can of course never prove something in science but the model seems to provide a reasonable explanation of our observations. There are of course definitely issues and things not yet understood and other things may turn out to be incorrect but that is the nature of science.
        stolio 12y ago
        > And you don't have to leave your frame of reference to see a difference between acceleration and gravity, they are distinguishable in any frame of reference. One of Einstein's great contributions is the knowledge that this isn't actually true. If you're in a box with no windows it's literally impossible to tell if you're on the ground in a planet's gravity or if you're being accelerated in empty space. http://en.wikipedia.org/wiki/Equivalence_principle http://en.wikipedia.org/wiki/Equivalence_principle
        12y ago
- xahrepap 12y ago
  My physics teacher did the same thing. When it came down to it, he was talking about vocabulary, not science. The definition of "force" he was trying to get across meant that there was no such thing as "centrifugal force".
  - ghshephard 12y ago
    Yeah, I get that he was teaching out of a book that told him (and probably every science teacher in existence) to teach this way - it just never made any sense. Anybody who has ever ridden a tilt-a-whirl instinctively knows there is a force pushing you out (otherwise you would go falling to the ground when it went vertical). Why science instructors are so focussed on the inwards force (in the case of a tilt-a-whirl, it's the outer frame, in the case of orbiting a planet/spinning neutron star, it's gravity) to the exclusion of everything else never made any sense to me, and caused me know end of distress. It probably came from the same place that suggested a charged item can attract a neutral object, but that a neutral object cannot attract a charged item. That made even less sense to me, but was right out of the book. Needless to say, my high school physics instructor and I never really got along very well.
    - EliRivers 12y ago
      Yeah, I get that he was teaching out of a book that told him (and probably every science teacher in existence) to teach this way - it just never made any sense. It makes an enormous amount of sense.
    - aptwebapps 12y ago
      If you tell someone there's no such thing as a centrifugal force and that (in rotation) there's only the centripetal force, you're half wrong. There's also ordinary inertia which is what is pushing you against the side of the tilt-a-whirl. Telling someone there's no such thing as the centrifugal force in physics is a good starting point but you shouldn't stop there.
      - tjradcliffe 12y ago
- deleted 12y ago
  [deleted]
- logicallee 12y ago
  if you haven't seen it yet this is an absolute gem - https://xkcd.com/123/ https://xkcd.com/123/
- GFK_of_xmaspast 12y ago
  That seems like a long time to carry such a petty grudge.
  - ghshephard 12y ago
    I ended up ignoring him for the next two years, thinking he was just a doofus who didn't know anything, as did many of my classmates. Probably missed out on a good physics education as a result.
bladedtoys 12y ago
While calling the bursts FRB is certainly descriptive, I kind of miss the whimsy of names like LGM [0] http://en.wikipedia.org/wiki/PSR_B1919%2B21 http://en.wikipedia.org/wiki/PSR_B1919%2B21
- TheOtherHobbes 12y ago
  See also: http://arxiv.org/pdf/1503.05245v2.pdf http://arxiv.org/pdf/1503.05245v2.pdf which suggests the FRB dispersions are quantised to a standard unit. A lot of newsies picked this up last week and suggested it was proof of... something unusual. The authors think it suggests the opposite. Given the date, I can't tell if the paper is serious or not. But if it's meant to be serious, the effect seems real - possibly an artefact of a very small sample size, but it's hard to tell. It would be useful to have access to the raw data to see the exact dispersion shape and frequency range, to check whether it matches - say - any standard radar chirp signal.
fullwedgewhale 12y ago
Just in time for the X-Files coming back this summer!

57 points by kposehn 12y ago

re: " If the star is above that critical mass but spinning, the centrifugal force can help keep the star from collapsing right away" I still resent my Grade 11/12 physics teacher for insisting that there was no such thing as centrifugal force, and that what was really occurring was centripetal acceleration only. He basically decided that newtons third law would not exist in his classroom.

pmalynin 12y ago
He's not entirely wrong. The thing with centrifugal force is that by picking a different frame of reference, it completely disappears and the reason it arises is due to your frame of reference being different. Interestingly, however, is that it is possible to pick a frame of reference such that gravity disappears, so it too is a fictitious force in a way.
- danbruc 12y ago
  Interestingly, however, is that it is possible to pick a frame of reference such that gravity disappears, so it too is a fictitious force in a way. I am not a physicist but that seems wrong to me or at least imprecise. You can select a frame of reference that makes gravitational forces disappear locally but there is no frame of reference that makes them go away globally.
  - jacquesm 12y ago
    That's the whole point of the exercise: to show that these frames of reference are all relative. And if you think about it, the exact point of origin of the 'big bang' might actually be a frame of reference relative to which gravity disappears globally. Relativity is a very tricky concept. Of course gravity is a 'real' force but the ability to shift your frame of reference is a powerful reminder that gravity and acceleration can look the same until you exit your frame of reference.
    - danbruc 12y ago
      I am not sure if I just misunderstand you, but we don't know if there was something like a singularity at the big bang and I would guess many doubt that there was. But if there was such a thing it was probably not at a specific point but everywhere. And you don't have to leave your frame of reference to see a difference between acceleration and gravity, they are distinguishable in any frame of reference.
      - SixSigma 12y ago
        You're also talking as though the "big bang" is proven.
        danbruc 12y ago
        Depends on how narrow or broad you interpret the term. I would say back to the origin of the cosmic microwave background 380,000 years past the big bang the story is pretty well understood. Back to ten to the minus thirty two seconds the model still looks reasonable to me. The time before that makes me feel uneasy, inflation looks to ad hoc to me as a laymen. And I really don't believe there was some kind of singularity with infinite density at the very beginning, but I doubt many do. You can of course never prove something in science but the model seems to provide a reasonable explanation of our observations. There are of course definitely issues and things not yet understood and other things may turn out to be incorrect but that is the nature of science.
      - stolio 12y ago
        > And you don't have to leave your frame of reference to see a difference between acceleration and gravity, they are distinguishable in any frame of reference. One of Einstein's great contributions is the knowledge that this isn't actually true. If you're in a box with no windows it's literally impossible to tell if you're on the ground in a planet's gravity or if you're being accelerated in empty space. http://en.wikipedia.org/wiki/Equivalence_principle http://en.wikipedia.org/wiki/Equivalence_principle
        12y ago
xahrepap 12y ago
My physics teacher did the same thing. When it came down to it, he was talking about vocabulary, not science. The definition of "force" he was trying to get across meant that there was no such thing as "centrifugal force".
- ghshephard 12y ago
  Yeah, I get that he was teaching out of a book that told him (and probably every science teacher in existence) to teach this way - it just never made any sense. Anybody who has ever ridden a tilt-a-whirl instinctively knows there is a force pushing you out (otherwise you would go falling to the ground when it went vertical). Why science instructors are so focussed on the inwards force (in the case of a tilt-a-whirl, it's the outer frame, in the case of orbiting a planet/spinning neutron star, it's gravity) to the exclusion of everything else never made any sense to me, and caused me know end of distress. It probably came from the same place that suggested a charged item can attract a neutral object, but that a neutral object cannot attract a charged item. That made even less sense to me, but was right out of the book. Needless to say, my high school physics instructor and I never really got along very well.
  - EliRivers 12y ago
    Yeah, I get that he was teaching out of a book that told him (and probably every science teacher in existence) to teach this way - it just never made any sense. It makes an enormous amount of sense.
  - aptwebapps 12y ago
    If you tell someone there's no such thing as a centrifugal force and that (in rotation) there's only the centripetal force, you're half wrong. There's also ordinary inertia which is what is pushing you against the side of the tilt-a-whirl. Telling someone there's no such thing as the centrifugal force in physics is a good starting point but you shouldn't stop there.
    - tjradcliffe 12y ago
deleted 12y ago
[deleted]
logicallee 12y ago
if you haven't seen it yet this is an absolute gem - https://xkcd.com/123/ https://xkcd.com/123/
GFK_of_xmaspast 12y ago
That seems like a long time to carry such a petty grudge.
- ghshephard 12y ago
  I ended up ignoring him for the next two years, thinking he was just a doofus who didn't know anything, as did many of my classmates. Probably missed out on a good physics education as a result.

bladedtoys 12y ago

While calling the bursts FRB is certainly descriptive, I kind of miss the whimsy of names like LGM [0] http://en.wikipedia.org/wiki/PSR_B1919%2B21 http://en.wikipedia.org/wiki/PSR_B1919%2B21

TheOtherHobbes 12y ago
See also: http://arxiv.org/pdf/1503.05245v2.pdf http://arxiv.org/pdf/1503.05245v2.pdf which suggests the FRB dispersions are quantised to a standard unit. A lot of newsies picked this up last week and suggested it was proof of... something unusual. The authors think it suggests the opposite. Given the date, I can't tell if the paper is serious or not. But if it's meant to be serious, the effect seems real - possibly an artefact of a very small sample size, but it's hard to tell. It would be useful to have access to the raw data to see the exact dispersion shape and frequency range, to check whether it matches - say - any standard radar chirp signal.

fullwedgewhale 12y ago

Just in time for the X-Files coming back this summer!