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Quasars outshine the galaxies they are in so 'tis difficult to get a handle on the size of such entities - this is all I am saying. The general portrayal is tha

Quasars outshine the galaxies they are in so 'tis difficult to get a handle on the size of such entities - this is all I am saying. The general portrayal is that they are smaller than solar system sizes. But that is an assumption that may be completely wrong. Even if hundreds of light years across, at the distances they are seen and in comparison to the sizes of galaxies, this is still small - almost point source in effect. Our own galaxy is, what, 150,000 to 200,000 light years across. The problem is the basis assumption. It is correct? Is it even valid? A lot more effort is required to determine this. It is a worthy area to investigate, don't you think?

Cogito 8y ago
> The general portrayal is that they are smaller than solar system sizes. But that is an assumption that may be completely wrong. What do you mean by this? People think they're that size because that's the size they've been measured at. There are different ways to measure a thing, and so far they all agree on the size, with no evidence to suggest otherwise. Are you suggesting they try and measure the size some other way?
- oldandtired 8y ago
  What are the error bounds on measuring such an object at the distances they exist at? > What do you mean by this? We make assumptions all the time when we measure things and often we do not question whether what we are measuring is actually correct. We assume. In these cases, we have to use proxies to determine distances and sizes. if any of those proxies are even a little out, our errors can be huge. > Are you suggesting they try and measure the size some other way? Not necessarily, but I am suggesting that the basis assumptions be looked at to see what else may be more applicable. If you do this, valuable insights may be gained and a different approach suggested. This kind of activity is undertaken for simple system like computer models. Why not do this for other such areas as well? Going back to my original comment, as the model does not accord with the data, maybe we need to be looking at the basis assumption that are being used. However, it appears that there are many who believe that the assumptions are true (for all intents and purposes) and can see no point as to question them. I have taken a strong interest in looking at the mathematical basis for much of our engineering and science. It is very obvious that the universe around at all levels is vastly more complicated than any of the mathematics we use to build our theories and models. That is not a problem, but it does mean that we need to clearly keep in mind that our theories and models are, at best, just an approximation and that we should not get caught up in believing that they are true but simply consider them as useful. When they are no longer useful, we can discard them for something more useful. Our understanding of the universe around will always be flawed. However, the fun is trying to get a handle on the universe by the models and theories we use. Too many people take themselves too seriously in the belief they put into the models and theories they ascribe to. If you are basing your reputation on being right about your model or theory, then I think you are taking the wrong approach to science. Offer up ideas to be investigated, let them be investigated. If they don't pan out then move on to something else. There is so much to look at at every level, let's have fun doing this. Don't be afraid t revisit old ideas or look at new ideas. There may be gems that will open up completely new areas of investigation and discovery.
  - Cogito 8y ago
    > What are the error bounds on measuring such an object at the distances they exist at? Let's look at two ways of judging the size of a quasar. We have photos of quasars, each at the middle of the galaxy they are at the centre of. We know the distance to the galaxy (and to the quasar) and can measure the size of the galaxy by the arc length it covers. Our errors on these measurements come down to how accurately we can measure the distance to galaxy and its size, but the quasar is very obviously much smaller than the galaxy. The other way is to look at how fast the luminosity of the quasar changes. If an object is observed to change at a certain rate (in the case of quasars, over the course of a few days sometimes) we have a limit on how big the object is. Looking for an upper limit, let's assume that the entire object changes at the same time; some process coordinates the change so that the whole thing gets brighter or dimmer at the same time. The light from each part of the object travels to us and arrives at different times. The parts that were close to us arrive first, the ones farther away last. Even an instantaneous change will be smeared out from the perspective of an observer, the bigger the smear the bigger the object. Importantly, the object (at least the light producing parts of the object, the parts we care about) can't be larger than implied by the smear. If it was bigger, the smear would be bigger. A smaller object can have a bigger smear, by slowing changing over time, but a bigger object can't have a smaller one. Quasars often change luminosity significantly on the order of weeks or days, so we know that they are no bigger than a few light-weeks or light-days across. For reference, our solar system is at least a light-day across, and by some definitions more than a light-year in size (or roughly half the way to the next star). > We make assumptions all the time when we measure things and often we do not question whether what we are measuring is actually correct. We assume. In these cases, we have to use proxies to determine distances and sizes. if any of those proxies are even a little out, our errors can be huge. Who is we in this case? Sure assumptions are made, all the time. When astronomers first started trying to measure distance to galaxies they assumed that all similar looking galaxies were the same size (the 'standard ruler' method). No one thought this was absolutely correct, but it was useful and allowed measurements to be made. Once you have those measurements you can compare with other measuring techniques and see if they agree. Sometimes changes will be made, but the errors are very very rarely 'huge'. As you walk towards a distant mountain, you are better able to see the slopes and craggy outline - it doesn't just disappear. > I am suggesting that the basis assumptions be looked at to see what else may be more applicable. If you do this, valuable insights may be gained and a different approach suggested. This kind of activity is undertaken for simple system like computer models. Why not do this for other such areas as well? Which 'basis assumptions' are you asking to be revisited here? In the article they walked through some of different theories that have been proposed to try and address the mechanics that underlie these objects. > Going back to my original comment, as the model does not accord with the data, maybe we need to be looking at the basis assumption that are being used. But the data does accord with the model! Up until this observation was made, the data very much did agree with what the model predicted. A new observation came up that showed some predictions were incorrect, but the model didn't suddenly become meaningless. Relativity showed that Newtonian physics didn't accurately describe fast moving objects, but Newtonian physics still accurately predicts almost everything else. > Don't be afraid t revisit old ideas or look at new ideas. There may be gems that will open up completely new areas of investigation and discovery. I don't disagree at all, but simply saying we need to reconsider our 'basis assumptions' doesn't do any of that. We have incredibly successful and accurate models, and are excited to find situations in which they don't hold up as that is an opportunity to improve our understanding of the world. But you go and investigate that specific failing, reworking the model to account for the difference. It is a rare and special thing to have to fundamentally change a model based on new observation, and there is no reason to suspect such a change is needed here, yet. Approaching any discrepancy between a model's prediction and an observation with "let's revisit our entire understanding of this subject" is neither useful nor scientific.
ceejayoz 8y ago
It's not an assumption, though. https://briankoberlein.com/2015/06/03/sizing-things-up/ https://briankoberlein.com/2015/06/03/sizing-things-up/ > Basically if an object is changing brightness, it can’t do that at a rate faster than the time it takes one side of the object to know what the other side is doing. That time is limited by the speed of light, so if you know the rate at which brightness varies, you know the maximum possible size of the object. Since these objects are also greatly redshifted we have to account for that as well (high redshift means time dilation), but that’s pretty easy to do. So we can take our quasar and AGN observations and calculate a maximum size for each one. Taking data for various quasars, I’ve plotted how many are at each particular size. While they vary in size, the most common size is most commonly around 5 on this graph, which equates to 100,000 AU, or about 1.5 light years across.
- oldandtired 8y ago
  > which equates to 100,000 AU, or about 1.5 light years across. This comment disputes the assumption that the quasar objects are only solar system sized as described in the original article. >> Basically if an object is changing brightness, it can’t do that at a rate faster than the time it takes one side of the object to know what the other side is doing. However, even this portion of the comment referenced is making an assumption that there has to be communication between the two sides. There is no requirement for such to actually occur, particularly if the effect is initiated at the central point and effects propagate outward. So if the assumption that quasars are black holes with accretion disks is incorrect, then the assumptions underlying the referenced comment can be completely irrelevant.
- Ono-Sendai 8y ago
  I read about an interesting counter-point to this a while ago. Imaging a ring of matter facing us, with a small source of radiation in the middle, which periodically emits a bunch of radiation. This radiation will strike the ring roughly at the same time, which is then re-rediated at us, in synchrony, even though the ring may very large (e.g. a light year across).

Cogito 8y ago

> The general portrayal is that they are smaller than solar system sizes. But that is an assumption that may be completely wrong. What do you mean by this? People think they're that size because that's the size they've been measured at. There are different ways to measure a thing, and so far they all agree on the size, with no evidence to suggest otherwise. Are you suggesting they try and measure the size some other way?

oldandtired 8y ago
What are the error bounds on measuring such an object at the distances they exist at? > What do you mean by this? We make assumptions all the time when we measure things and often we do not question whether what we are measuring is actually correct. We assume. In these cases, we have to use proxies to determine distances and sizes. if any of those proxies are even a little out, our errors can be huge. > Are you suggesting they try and measure the size some other way? Not necessarily, but I am suggesting that the basis assumptions be looked at to see what else may be more applicable. If you do this, valuable insights may be gained and a different approach suggested. This kind of activity is undertaken for simple system like computer models. Why not do this for other such areas as well? Going back to my original comment, as the model does not accord with the data, maybe we need to be looking at the basis assumption that are being used. However, it appears that there are many who believe that the assumptions are true (for all intents and purposes) and can see no point as to question them. I have taken a strong interest in looking at the mathematical basis for much of our engineering and science. It is very obvious that the universe around at all levels is vastly more complicated than any of the mathematics we use to build our theories and models. That is not a problem, but it does mean that we need to clearly keep in mind that our theories and models are, at best, just an approximation and that we should not get caught up in believing that they are true but simply consider them as useful. When they are no longer useful, we can discard them for something more useful. Our understanding of the universe around will always be flawed. However, the fun is trying to get a handle on the universe by the models and theories we use. Too many people take themselves too seriously in the belief they put into the models and theories they ascribe to. If you are basing your reputation on being right about your model or theory, then I think you are taking the wrong approach to science. Offer up ideas to be investigated, let them be investigated. If they don't pan out then move on to something else. There is so much to look at at every level, let's have fun doing this. Don't be afraid t revisit old ideas or look at new ideas. There may be gems that will open up completely new areas of investigation and discovery.
- Cogito 8y ago
  > What are the error bounds on measuring such an object at the distances they exist at? Let's look at two ways of judging the size of a quasar. We have photos of quasars, each at the middle of the galaxy they are at the centre of. We know the distance to the galaxy (and to the quasar) and can measure the size of the galaxy by the arc length it covers. Our errors on these measurements come down to how accurately we can measure the distance to galaxy and its size, but the quasar is very obviously much smaller than the galaxy. The other way is to look at how fast the luminosity of the quasar changes. If an object is observed to change at a certain rate (in the case of quasars, over the course of a few days sometimes) we have a limit on how big the object is. Looking for an upper limit, let's assume that the entire object changes at the same time; some process coordinates the change so that the whole thing gets brighter or dimmer at the same time. The light from each part of the object travels to us and arrives at different times. The parts that were close to us arrive first, the ones farther away last. Even an instantaneous change will be smeared out from the perspective of an observer, the bigger the smear the bigger the object. Importantly, the object (at least the light producing parts of the object, the parts we care about) can't be larger than implied by the smear. If it was bigger, the smear would be bigger. A smaller object can have a bigger smear, by slowing changing over time, but a bigger object can't have a smaller one. Quasars often change luminosity significantly on the order of weeks or days, so we know that they are no bigger than a few light-weeks or light-days across. For reference, our solar system is at least a light-day across, and by some definitions more than a light-year in size (or roughly half the way to the next star). > We make assumptions all the time when we measure things and often we do not question whether what we are measuring is actually correct. We assume. In these cases, we have to use proxies to determine distances and sizes. if any of those proxies are even a little out, our errors can be huge. Who is we in this case? Sure assumptions are made, all the time. When astronomers first started trying to measure distance to galaxies they assumed that all similar looking galaxies were the same size (the 'standard ruler' method). No one thought this was absolutely correct, but it was useful and allowed measurements to be made. Once you have those measurements you can compare with other measuring techniques and see if they agree. Sometimes changes will be made, but the errors are very very rarely 'huge'. As you walk towards a distant mountain, you are better able to see the slopes and craggy outline - it doesn't just disappear. > I am suggesting that the basis assumptions be looked at to see what else may be more applicable. If you do this, valuable insights may be gained and a different approach suggested. This kind of activity is undertaken for simple system like computer models. Why not do this for other such areas as well? Which 'basis assumptions' are you asking to be revisited here? In the article they walked through some of different theories that have been proposed to try and address the mechanics that underlie these objects. > Going back to my original comment, as the model does not accord with the data, maybe we need to be looking at the basis assumption that are being used. But the data does accord with the model! Up until this observation was made, the data very much did agree with what the model predicted. A new observation came up that showed some predictions were incorrect, but the model didn't suddenly become meaningless. Relativity showed that Newtonian physics didn't accurately describe fast moving objects, but Newtonian physics still accurately predicts almost everything else. > Don't be afraid t revisit old ideas or look at new ideas. There may be gems that will open up completely new areas of investigation and discovery. I don't disagree at all, but simply saying we need to reconsider our 'basis assumptions' doesn't do any of that. We have incredibly successful and accurate models, and are excited to find situations in which they don't hold up as that is an opportunity to improve our understanding of the world. But you go and investigate that specific failing, reworking the model to account for the difference. It is a rare and special thing to have to fundamentally change a model based on new observation, and there is no reason to suspect such a change is needed here, yet. Approaching any discrepancy between a model's prediction and an observation with "let's revisit our entire understanding of this subject" is neither useful nor scientific.

ceejayoz 8y ago

It's not an assumption, though. https://briankoberlein.com/2015/06/03/sizing-things-up/ https://briankoberlein.com/2015/06/03/sizing-things-up/ > Basically if an object is changing brightness, it can’t do that at a rate faster than the time it takes one side of the object to know what the other side is doing. That time is limited by the speed of light, so if you know the rate at which brightness varies, you know the maximum possible size of the object. Since these objects are also greatly redshifted we have to account for that as well (high redshift means time dilation), but that’s pretty easy to do. So we can take our quasar and AGN observations and calculate a maximum size for each one. Taking data for various quasars, I’ve plotted how many are at each particular size. While they vary in size, the most common size is most commonly around 5 on this graph, which equates to 100,000 AU, or about 1.5 light years across.

oldandtired 8y ago
> which equates to 100,000 AU, or about 1.5 light years across. This comment disputes the assumption that the quasar objects are only solar system sized as described in the original article. >> Basically if an object is changing brightness, it can’t do that at a rate faster than the time it takes one side of the object to know what the other side is doing. However, even this portion of the comment referenced is making an assumption that there has to be communication between the two sides. There is no requirement for such to actually occur, particularly if the effect is initiated at the central point and effects propagate outward. So if the assumption that quasars are black holes with accretion disks is incorrect, then the assumptions underlying the referenced comment can be completely irrelevant.
Ono-Sendai 8y ago
I read about an interesting counter-point to this a while ago. Imaging a ring of matter facing us, with a small source of radiation in the middle, which periodically emits a bunch of radiation. This radiation will strike the ring roughly at the same time, which is then re-rediated at us, in synchrony, even though the ring may very large (e.g. a light year across).