On The Relativity of Redshifts: Does Space Really “Expand”?

I've written an article 'On the Relativity of Redshifts: Does Space Really "Expand"?' which has appeared in Australian Physics (2016, 53(3), 95-100). For some reason, the arXiv has put the article on hold, so you can download it here.


I like it :)
Location: Sydney NSW, Australia

Comments

  1. Phillip Helbig27 May 2016 at 04:07

    Haven't read it yet, but will do so soon. Surprised that the references contain neither Harrison's ApJ paper nor Bunn and Hogg.

    More later.

    And do let me know why the paper was put on hold, if you ever find out, and let me know when it shows up on arXiv. Personal email would be best (and post here as well if you want).

    ReplyDelete
    Replies
    1. Cusp27 May 2016 at 07:42

      It's a semi-popular level article, not a paper. The goal was not to provide a complete review of the literature, but an overview. Hence, not that many fires to my own work :)

      Delete
  2. Phillip Helbig27 May 2016 at 05:18

    In this corner, we have Peacock, Rees, and Weinberg. And in this corner, we have Harrison, certainly no slouch. Here and in his textbook, Harrison defends the expanding-space view.

    Bunn and Hogg have written a paper which takes the opposite point of view, and explains Narlikar's work in a more accessible way.

    For me, the idea of an empty universe which is expanding is "proof" that space expands. Yes, it can be transformed away, but I still think that it is a useful picture. In particular, the entire concept of horizons, as well as questions like "how can this galaxy be receding at more than the speed of light", are easier to understand in this picture.

    At the end of the day, does it matter? You mention that developing an intuition is important, and I agree. However, different intuitions work for different people. Some want to see an equation, some want to make a plot, some want a series of figures. Some think mathematically, some not; some visually, some not. What really matters is whether one gets the right answer. Like polar and cartesian coordinates, it is not so much a question of which is right as of which is more convenient (in a particular situation).

    Yes, abusing the expanding-space picture can lead to wrong results, but so can abusing a model which does not include expanding space. I'm sure that all interesting results can be derived in the expanding-space picture as well.

    An analogy is perhaps the membrane paradigm with respect to black holes. It's a different picture, but can be useful. Or different interpretations of quantum mechanics. As long as the calculations turn out correctly, does it matter?

    ReplyDelete
    Replies
    1. Cusp27 May 2016 at 07:44

      Some talk about expanding space as a "thing" and that, simply, is wrong. It's a picture for some, and that is all.

      Delete
  3. Phillip Helbig29 June 2016 at 19:26

    Consider a universe with a positive cosmological constant, lambda, > 1, and zero matter density. This is the Lanczos model, an empty bounce model. At least in the expanding-space view, it has a definite volume, measured in pints if you like, which changes with time. There is no matter in it. The energy density due to the cosmological constant does not change with time.

    How can one describe this without using the expanding-space view?

    ReplyDelete
  4. Unknown16 February 2017 at 22:09

    Midbrain Activation Academy
    Midbrain Activation Academy
    Midbrain Activation Academy
    Midbrain Activation Academy
    Midbrain Activation Academy
    Midbrain Activation Academy
    Midbrain Activation Academy

    ReplyDelete
  5. Anonymous29 January 2018 at 22:07

    kiss day hd images with quotes
    kisss day love images download
    best hug day quotes for her
    funny happy hug day quotes

    ReplyDelete
  6. Bmarkify17 November 2024 at 03:29

    Great article! I thoroughly enjoyed the detailed exploration of redshifts and the thought-provoking insights into the nature of space expansion. It’s fascinating to dive into the nuances of cosmic phenomena and how they shape our understanding of the universe.

    If you’re interested in engaging with more cosmic-themed content, you might also enjoy our blog on Cosmos Persona Quiz Where & How to Play. It’s a fun and interactive way to connect with the mysteries of the cosmos and uncover your cosmic persona.

    Looking forward to more enlightening posts on your blog! Keep up the great work.

    ReplyDelete

Post a Comment

Popular posts from this blog

Falling into a black hole: Just what do you see?

Image
Everyone loves black holes. Immense gravity, a one-way space-time membrane, the possibility of links to other universes. All lovely stuff. A little trawl of the internets reveals an awful lot of web pages discussing black holes, and discussions about spaghettification, firewalls, lost information, and many other things. Actually, a lot of the stuff out there on the web is nonsense, hand-waving, partly informed guesswork. And one of the questions that gets asked is "What would you see looking out into the universe?" Some (incorrectly) say that you would never cross the event horizon, a significant mis-understanding of the coordinates of relativity. Other (incorrectly) conclude from this that you actually see the entire future history of the universe play out in front of your eyes. What we have to remember, of course, is that relativity is a mathematical theory, and instead of hand waving, we can use mathematics to work out what we will see. And that's what I did. ...
Read more

Journey to the Far-Side of the Sun

Image
There was a movie, in the old days, Journey to the Far-Side of the Sun  (also known as Doppleganger) which (spoiler alert) posits that there is a mirror version of the Earth hidden on the other side of the Sun, sharing the orbit with our Earth. The idea is that this planet would always be hidden behind the Sun, and so we would not know it there there. This idea comes up a lot, over and over again. In fact, it came up again last week on twitter. But there's a problem. It assumes the Earth is on a circular orbit. I won't go into the details here, but one of the greatest insights in astronomy was the discovery of Kepler's laws of planetary motion , telling us that planets move on elliptical orbits. With this, there was the realisation that planets can't move at uniform speeds, but travel quickly when closer to the Sun, while slowing down as their orbits carry them to larger distance.  There has been a lot of work examining orbits in the Solar System, and you can  s...
Read more

Moving Charges and Magnetic Fields

Image
Still struggling with grant writing season, so another post which has resulted in my random musings about the Universe (which actually happens quite a lot). In second semester, I am teaching  electricity and magnetism to our First Year Advanced Class . I really enjoy teaching this class as the kids are on the ball and can ask some deep and meaningful questions. But the course is not ideal. Why? Because we teach from a textbook and the problem is that virtually all modern text books are almost the same. Science is trotted out in an almost historical progression. But it does not have to be taught that way. In fact, it would be great if we could start with  Hamiltonian and Lagrangian  approaches, and derive physics from a top down approach. We're told that it's mathematically too challenging, but it really isn't. In fact, I would start with a book like  The Theoretical Minimum , not some multicoloured compendium of physics. We have to work with what we have! ...
Read more