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> The idea may be plausible, but it comes with a big problem: it can't be tested. Doesn't that imply that the accepted model can't be tested? I mean, in the se

> The idea may be plausible, but it comes with a big problem: it can't be tested. Doesn't that imply that the accepted model can't be tested? I mean, in the sense of distinguishing it from this one.

oarla 8y ago
Not a physicist, but I recall reading that there is enough empirical evidence to support the current model of expanding universe.
- mirimir 8y ago
  OK. But if that evidence were adequate to exclude this new hypothesis, then one could reject it. And TFA says that one can't. That implies that existing empirical evidence is just as consistent with the new hypothesis as it is with the accepted one.
- DougN7 8y ago
  I always wonder about that. I remember very specifically learning 40(?) years ago that the expansion was slowing, supposedly proven by some sort of red shift in light. That is now out of favor, but a few more new facts just might swing things the other way again.
  - pdonis 8y ago
    > That is now out of favor It's not "out of favor" just as a matter of fashion: a lot more data was collected, extending much further away and therefore much further into the past. > a few more new facts just might swing things the other way again. No, it would take a lot more than that, because our current model of accelerating expansion for the past few billion years (note that before that, the expansion was decelerating) is based on a lot more data than we had 40 or so years ago.
  - sanxiyn 8y ago
    Accelerating universe is supported by supernova data. We have incomparably more supernova data compared to the past. Discovery of accelerating universe was mainly due to radically scaling up supernova discovery process.
    - madaxe_again 8y ago
      Yes, but that’s still dependent on a differential velocity model for the origin of redshift. This paper changes that core assumption, meaning the same data can be interpreted to have a radically different meaning. Afaik, we have no direct observations of galaxies moving away from us - over such enormous distances we have not had enough time since the start of observations to actually see a galaxy recede.
      - gcthomas 8y ago
        No, the origin of the cosmological redshift is not proposed to be due to differences in velocity, but metric expansion.
        platz 8y ago
        ... which causes a change in relative velocities
        gcthomas 8y ago
        That makes it sound like cosmological redshift is a form of Doppler shift. In reality, the target object emits light towards us with little Doppler shift as it will have experienced little acceleration in its reference frame. The light becomes redshifted as it moves through the universe while the universe is expanding, effectively stretching out the wavelength of the light. The change in wavelength is exactly proportional to the increase in size of the universe during the time of flight, and it is not directly related to speed of recession except in common and inaccurate discussion. The link to relative velocity (if that concept makes sense for objects in widely separated and unrelated reference frames) is model dependent, while the metric expansion measurement is directly measured.
yk 8y ago
Yes, depending on your favorite definition of "different model" there are models that can not be distinguished even in principle. Most famous example is the different interpretations of quantum mechanics. In my opinion the reasonable way to deal with that, is to assume that they are the same model since they describe the same physics and leave the semantics to the philosophers.
- mirimir 8y ago
  Yeah, I was thinking along similar lines, but it seemed too outrageous. The various interpretations of QM are so-far indistinguishable because they're based on the same (or equivalent) mathematics, and so make the same predictions. This one, though. I mean, the fundamental observation is that red shift increases with distance. The accepted model has red shift caused by motion away from us, and so we conclude that recessional velocity increases with distance. That is, the Universe is expanding. This new model has blue shift caused by increasing mass. And so we are blue-shifted relative to distant stuff, which we see only in the past. So it looks red-shifted to us. And distance is proportional to time delay, so stuff that's farther away is more red-shifted. Bu I don't see how the temporal rate of mass increase could be related to -- or rather, another reflection of -- the expansion of the Universe. But then, IANAP, so hey.

> The idea may be plausible, but it comes with a big problem: it can't be tested. Doesn't that imply that the accepted model can't be tested? I mean, in the sense of distinguishing it from this one.

oarla 8y ago

Not a physicist, but I recall reading that there is enough empirical evidence to support the current model of expanding universe.

mirimir 8y ago
OK. But if that evidence were adequate to exclude this new hypothesis, then one could reject it. And TFA says that one can't. That implies that existing empirical evidence is just as consistent with the new hypothesis as it is with the accepted one.
DougN7 8y ago
I always wonder about that. I remember very specifically learning 40(?) years ago that the expansion was slowing, supposedly proven by some sort of red shift in light. That is now out of favor, but a few more new facts just might swing things the other way again.
- pdonis 8y ago
  > That is now out of favor It's not "out of favor" just as a matter of fashion: a lot more data was collected, extending much further away and therefore much further into the past. > a few more new facts just might swing things the other way again. No, it would take a lot more than that, because our current model of accelerating expansion for the past few billion years (note that before that, the expansion was decelerating) is based on a lot more data than we had 40 or so years ago.
- sanxiyn 8y ago
  Accelerating universe is supported by supernova data. We have incomparably more supernova data compared to the past. Discovery of accelerating universe was mainly due to radically scaling up supernova discovery process.
  - madaxe_again 8y ago
    Yes, but that’s still dependent on a differential velocity model for the origin of redshift. This paper changes that core assumption, meaning the same data can be interpreted to have a radically different meaning. Afaik, we have no direct observations of galaxies moving away from us - over such enormous distances we have not had enough time since the start of observations to actually see a galaxy recede.
    - gcthomas 8y ago
      No, the origin of the cosmological redshift is not proposed to be due to differences in velocity, but metric expansion.
      - platz 8y ago
        ... which causes a change in relative velocities
        gcthomas 8y ago
        That makes it sound like cosmological redshift is a form of Doppler shift. In reality, the target object emits light towards us with little Doppler shift as it will have experienced little acceleration in its reference frame. The light becomes redshifted as it moves through the universe while the universe is expanding, effectively stretching out the wavelength of the light. The change in wavelength is exactly proportional to the increase in size of the universe during the time of flight, and it is not directly related to speed of recession except in common and inaccurate discussion. The link to relative velocity (if that concept makes sense for objects in widely separated and unrelated reference frames) is model dependent, while the metric expansion measurement is directly measured.

yk 8y ago

Yes, depending on your favorite definition of "different model" there are models that can not be distinguished even in principle. Most famous example is the different interpretations of quantum mechanics. In my opinion the reasonable way to deal with that, is to assume that they are the same model since they describe the same physics and leave the semantics to the philosophers.

mirimir 8y ago
Yeah, I was thinking along similar lines, but it seemed too outrageous. The various interpretations of QM are so-far indistinguishable because they're based on the same (or equivalent) mathematics, and so make the same predictions. This one, though. I mean, the fundamental observation is that red shift increases with distance. The accepted model has red shift caused by motion away from us, and so we conclude that recessional velocity increases with distance. That is, the Universe is expanding. This new model has blue shift caused by increasing mass. And so we are blue-shifted relative to distant stuff, which we see only in the past. So it looks red-shifted to us. And distance is proportional to time delay, so stuff that's farther away is more red-shifted. Bu I don't see how the temporal rate of mass increase could be related to -- or rather, another reflection of -- the expansion of the Universe. But then, IANAP, so hey.