I Regarding the accuracy of the description of a pulsar in a 1977 paper

[tade]

I was reading this 1977 paper about a method of trying to test the speeds of light by making use of pulsars, in it the author Kenneth Brecher describes a model of a pulsar, and I'm wondering about its accuracy and I'd like to double-check.

In the second page, the left column, the upper part, he writes: "Let one of the sources emit pulses at a constant rate in its own rest frame."

And this description strikes me as rather odd, because I had thought that pulsars don't actually pulse and they just rotate continuously like a lighthouse, to use the lighthouse analogy, and in the paper Brecher seems to have described a model which pulses literally.

And so what are your thoughts on the accuracy of the pulsar model, interestingly I think that there is something significant about the description of the model, though yet at the same time it seems too significant an issue to be one for a published paper, of an MIT prof and especially in a publication such as Physical Review Letters in the 1970's

 

[Ibix]

I had thought that pulsars don't actually pulse and they just rotate continuously like a lighthouse,

They do - the beam sweeps out a cone.

in the paper Brecher seems to have described a model which pulses literally.

I don't see a problem. Imagine a giant mirror between the Earth and the pulsar that would block our view of it, except it has a hole in it that happens to be on the line between Earth and the pulsar. All parts of the beam that aren't pointed at Earth are reflected and we do then have a pulse stream. But what we see on Earth is the same whether the mirror is there or not.

So it's an incorrect description, but I don't see any consequences relevant to the point he's making.

 

[renormalize]

In the second page, the left column, the upper part, he writes: "Let one of the sources emit pulses at a constant rate in its own rest frame."

And this description strikes me as rather odd, because I had thought that pulsars don't actually pulse and they just rotate continuously like a lighthouse, to use the lighthouse analogy, and in the paper Brecher seems to have described a model which pulses literally.

I think the author's analysis is framed in terms of the orbital velocities of the emitters and is insensitive to whether the received pulses are due to a rotating "lighthouse beam" or some other mechanism like, e.g., radial pulsations of the emitters. Hence, he only needs the fact that we observe regular pulses from the emitters, irrespective of their detailed cause.

 

[tade]

I don't see a problem. Imagine a giant mirror between the Earth and the pulsar that would block our view of it, except it has a hole in it that happens to be on the line between Earth and the pulsar. All parts of the beam that aren't pointed at Earth are reflected and we do then have a pulse stream. But what we see on Earth is the same whether the mirror is there or not.

So it's an incorrect description, but I don't see any consequences relevant to the point he's making.

hmm i see, and i'm also thinking that the switch to a basic lighthouse-model also comes with some additional parameters, such as:

- the direction of the vector of the angular momentum of the pulsar (parallel with the rotational axis)
- the angle between the rotational axis and the emission axis
- if the neutron star had no rotation, the relationship between the direction and the intensity of an emission, which would be the angle between said direction and the emission axis
- the radius of the neutron star, which would affect the tangential velocities as star rotates

and what effects do you think such parameters would have on the velocities and intensities (the intensities as a function of time) of rays of the stream (i guess if assuming an emission theory of light)
and i was thinking that all these parameters might have effects on each other for the overall calculations and results

also what are your thoughts on the notion that sometimes figuring out the basic properties of astronomical objects relies on assumptions about the theory of light used to infer those basic properties, as the theory can have effects on the visual observations and our interpretations of those observations that we make, and hence, if its the theory of light that's being tested, that it might also have effects on what we can infer about the basic properties

 

[tade]

I think the author's analysis is framed in terms of the orbital velocities of the emitters and is insensitive to whether the received pulses are due to a rotating "lighthouse beam" or some other mechanism like, e.g., radial pulsations of the emitters. Hence, he only needs the fact that we observe regular pulses from the emitters, irrespective of their detailed cause.

oh i see, and so speaking of the significance of their detailed causes, i was thinking about certain considerations as described above in #4

 

[Ibix]

what effects do you think such parameters would have on the velocities and intensities (the intensities as a function of time) of rays of the stream (i guess if assuming an emission theory of light)

They all might affect the period of the pulsar, but the only fact about the period being used is that it doesn't change. The point about emission theory is that light has a variable speed, so some pulses from the pulsar are going faster than others and overtake earlier ones. We never see this.

It's certainly possible to imagine circumstances where variation in pulsar pulse rate cancels out speed-induced arrival time variation. But such a thing is distance and angle dependent - the cancellation would only be exact at a particular distance and observers at other places would see timing variation. So you'd need to explain why it always happens for Earth. Not to mention stacks of other lines of evidence suggesting emission theory is wrong.

also what are your thoughts on the notion that sometimes figuring out the basic properties of astronomical objects relies on assumptions about the theory of light used to infer those basic properties, as the theory can have effects on the visual observations and our interpretations of those observations that we make, and hence, if its the theory of light that's being tested, that it might also have effects on what we can infer about the basic properties

I think that if the only available sources of EM radiation were astronomical objects, or there were no such thing as artificial satellites and space probes, you might have a point. But we can study light from terrestrial sources and we can study light from sources in space that we control, and it all behaves the same way.

More generally "different rules might apply to situation X" will always be met with "yes of course - so what rules did you have in mind?" Emission theory provides a set of rules for how light behaves that can be used to make predictions. Those predictions don't match any experiment we've ever done that's capable of discriminating it.