“Nothing is too wonderful to be true, if it be consistent with the laws of nature.” –Michael Faraday

And yet, it’s often incredibly difficult to use those laws of nature — even if they’re as simple as can be — to actually measure and quantitatively understand the Universe around us. Perhaps one of the most glaring examples is magnetism.

Image credit: Alexander Wilmer Duff, 1916.

Image credit: Alexander Wilmer Duff, 1916.

Sure, it’s easy to visualize a magnetic field if you’ve got a set of iron filings and a laboratory to experiment in, but what about the distant stars? What of entire galaxies? They’re thought to have magnetic fields, just as our Sun does. But we can’t measure the coronal loops so easily for objects thousands, millions or billions of times as distant.

Image credit: NASA / Transition Region And Coronal Explorer (TRACE).

Image credit: NASA / Transition Region And Coronal Explorer (TRACE).

Yet, we have our techniques, based on how light interacts with magnetic fields. Come see how we map the Universe’s magnetism from afar!

Comments

  1. #1 Mark
    January 25, 2015

    human machines which create magnetism must affect the earths magnetism? So, i’m mainly speaking about MRI scanning machines. But virtually everything has a magnetic field, they must affect each other. The more magnetic devices we use the more affect it has on earths magnetism. Perhaps this is why the earths magnetism is decreasing. What are your thoughts?

  2. #2 Mark
    January 25, 2015

    I have been pondering on this for some years now. Machines which create magnetism must affect the earths magnetism(?). I propose that Machines such as MRI scanners create high magnetism, virtually everything has a magnetic field, they must have affects on each other. The more magnetic devices humans use around the earth, the more affect it can have on earths magnetism (core). Perhaps this is why the earths magnetism is decreasing. What are your thoughts?

  3. #3 Michael Kelsey
    SLAC National Accelerator Laboratory
    January 25, 2015

    @Mark #1 and #2: No. No, they don’t. And you can do the math to figure out why; it’s not magic (despite Bill O’Reilly’s professions of ignorance).

    Magnetic fields decrease with distance much faster than 1/r^2. A simple dipole magnet (a bar magnet, or a coil of wire), the variation is 1/r^3. For more complex fields, such as those of MRI machines, hydropower turbines, etc., the field falls off much faster even than that.

    Consider that a typical MRI machine is in a ~5 x 5 m room, and the field outside that room is small enough not to bother people (and their electronics!) sitting around waiting. So we can guess that an MRI machine has an “effective range” of maybe 7 m or so.

    The Earth’s core is 6300 km away from the surface, or 6,300,000 m. That’s 900,000 times farther than the “effective range” of an MRI machine. So, no, human machines don’t affedt the Earth’s magnetic field.

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