The middle size of the universe

From Kevin Kelly’s book What Technology Wants:

Our body size is, weirdly, almost exactly in the middle of the size of the universe. The smallest things we know about are approximately 30 orders of magnitude smaller than we are, and the largest structures in the universe are about 30 orders of magnitude bigger.

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16 thoughts on “The middle size of the universe

  1. Seconded, Zeno, or if not exactly observation bias, the reflection of a natural tendency for our knowledge to advance from the most familiar outward.

  2. I thought about observation bias, but I don’t think that’s an issue here. If blue whales were able to measure the age (hence the size) of the universe, I don’t see why they would find the universe younger or older than we do. And I don’t see why whales would measure things like Plank’s constant any differently than we do. Sentient whales might use different units of measure, presumably larger units, but Kelly’s observation has nothing to do with units of measurement.

  3. So what?

    @Whales. If the human scale is 2m and the whale scale is 20m, isn’t a whale almost exactly in the middle of the scale too?

    What’s is the lower bound?
    The Planck length is 10^-35m.
    An electron is say 10^-20m.

    What is the upper bound?
    The radius of the observable universe is apparently 46 billion light years
    Which I reckon is 4×10^26m

    Maybe I’ve got something wrong.

  4. Mat: You are correct that whales are not several orders of magnitude larger than humans, so my analogy is weak. But I still don’t see why a larger creature, say one the size of a planet, would come up with a different age/size of the universe. I think the top end of the scale is fixed.

    The bottom end of the scale is fuzzier since it’s not clear what to consider the smallest “thing”.

  5. If you consider the largest thing to be the largest galaxy rather than the universe itself, and if you consider the smallest thing an electron, then you could say we’re in the middle between things 20 orders of magnitude larger and smaller.

  6. Why would you exclude galactic clusters and superclusters, and walls and voids? The Sloan Great Wall is 1.37 billion light years or 1.30×10^25 m. in length.

  7. I think the initial size matters a great deal. For humans, I would expect the progression to go something like: Human. Part of a human (arm). Hand. Finger. Knuckle. Skin. Skin Cell. and on down.

    For a planet, I would imagine it to be: Planet. Atmosphere. Ground. Water. River. etc.

    Basically assuming that we start at what is familiar and progress to smaller and smaller items. If we’ve gone 20 levels deep, for arguments sake, I would think that a planetary being might go 20 levels deep as well, just that their 20 levels are maybe quite a bit off (in orders of magnitude) from how far we’ve gone, as we have.

    I don’t think our current understanding of largest and smallest things represent everything. I think they represent, as @Jason said, working out from our own vantage point.

  8. there is something wrong with writing “orders of magnitude” and “almost exactly” in the same paragraph.

  9. Vak: I agree that “order of magnitude” is often used to mean “rough approximation” and that there would be a contradiction in using “roughly” and “exactly” in the same sentence.

    But a popular writer like Kelly could use the phrase “orders of magnitude” as a non-technical way of saying “on a logarithmic scale.” I imagine that was his intent. Even so, it does seem that “almost exactly” was an overstatement.

  10. John, It’s observation bias in the sense that had we not been in the middle, we wouldn’t have noted it and pointed it out. We happen to be in the middle, so it seems special.

    A blue whale may not find itself in the middle of the length scale, but it may find itself in the middle of some other scale (not necessarily lengthwise – could be mass, temporal, or something equally arbitrary).

  11. It’s observation bias in the sense that we are in the middle between the smallest and largest *measurable* things, where it us who are doing the measuring. Do scientists really believe they know the final extent of the universe? Surely we’ve just seen the tip of the iceberg.

  12. We know how old the universe is, and we know what its expansion rate has been over time, so we do have pretty good idea how big the universe is, unless we’re wrong about our premises.

    On the small end, maybe our intelligence rather than our physical size keeps us from knowing what’s going on at smaller scales. We’re looking at things so many orders of magnitude smaller than we are, it doesn’t seem that it would make much difference if we were a few orders of magnitude larger or smaller. Maybe if we were giants, we’d find it easier to build large accelerators and would have built them sooner.

  13. Imagine a scientifically advanced species of microscopic beings living on some tiny speck deep within a breadcrumb lying in a discarded lunch sack buried a few feet deep in a pile of trash out in the middle of nowhere. They can see microscopic things with the naked eye. Their microscopes are no more sophisticated than ours but they have a huge head start by being so small. They also have tiny telescopes with which they’ve discovered other breadcrumbs and various other mysterious items. Through clever means, their scientists have determined the size of the universe. It’s huge—almost a foot wide (it’s a lunch sack). There is consensus about its age, too: it seems to have been plopped down here about 13 billion quuxes ago. One of the microscopic beings has recently noticed his species, size-wise, sits roughly in the middle of the smallest and largest known thing…

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