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arXiv:astro-ph/0310808astro-ph

Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe

Tamara M. Davis, Charles H. Lineweaver

Abstract

We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the Universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard Lambda-CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ``observable universe'' and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23 sigma.

arXiv comments
To appear in Publications of the Astronomical Society of Australia, 26 pages (preprint format), 6 figures. Version 2: Section 4.1 revised
Journal reference
DOI
doi:10.1071/AS03040
Subjects
astro-phAstrophysics

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Linked by 6 identifiable commenters in 10 comments across 9 threads, from Jul 2011 to Oct 2024.

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Discussed in comments9 threads

  1. On the Nature of Time 1 comment
  2. Webb captures iconic Horsehead Nebula in unprecedented detail 1 comment

    • > The density in the observed universe is used to extrapolate the number of galaxies in the non-observed universe. As has already been pointed out, our best current model of our universe is that it is spatially infinite. That means an infinite number of galaxies. The finite…

      pdonisView on HNParent context

  3. Astronomers posit that we live in an area with below average density 1 comment

    • > Your statement that matter has average uniform density in all directions around us is obviously only correct in sufficiently large frames of reference Yes, agreed. But the distance to our cosmological horizon is large enough that the averaging assumption is fine on that scale.…

      pdonisView on HNParent context

  4. Shouldn't distant objects appear magnified? 1 comment

    • This educational paper [0] titled "Expanding Confusion" (2003) is a classic on the general topic and well worth the read. Holding the two concepts of an accelerated (!) (in terms of objects [1]) expanding universe and the fixed finite speed of light simultaneously in one's…

      dav_OzView on HNParent context

  5. 12 Billion-year-old signal from the end of the universe's 'dark age' 1 comment
  6. Astronomers report the most distant radio galaxy ever discovered 1 comment

    • Here: "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe" https://arxiv.org/abs/astro-ph/0310808

      jobigoudView on HNParent context

  7. Olbers' paradox 1 comment

    • > If two points are so far apart that the expansion of space inflates the distance between them faster than light can cross it, then no light can ever reach from one to the other, even if it travels for an infinitely long time Actually, it can. The issue is quite subtle. What…

      jobigoudView on HNParent context

  8. How big is the entire universe? 2 comments

    • The short answer is nobody has a plausible upper bound on the size of the entire Universe, and there's no firm consensus on whether it's literally infinite. If it is finite, there is no "wall" or "center", since it's not a big sphere -- a finite Universe just means that if you…

      goodsideView on HNParent context

    • This is a misconception. If you just want a satisfying mental image of the Universe: It's really big, it doesn't have any point defined as its center, and it doesn't have any wall-like borders. Aliens living 14.6 billion LY away from us see a Universe that looks just like what…

      goodsideView on HNParent context

  9. Giant body of water found in space, black hole claims it was just hydrating 1 comment

    • The answers to the first two questions are related, and unfortunately complicated. I was almost referring to the Cosmic Microwave Background Radiation (CMBR), but I actually meant a slightly older event, the end of the inflationary epoch. The inflationary epoch is rarely…

      goodsideView on HNParent context

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