[HN Gopher] The (likely?) cheapest home-made Michelson interfero...
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The (likely?) cheapest home-made Michelson interferometer
Author : LolWolf
Score : 64 points
Date : 2026-01-04 20:49 UTC (5 days ago)
(HTM) web link (guille.site)
(TXT) w3m dump (guille.site)
| RationPhantoms wrote:
| Same physics principles used to measure gravitational waves at
| LIGO (Laser Interferometer Gravitational-Wave Observatory)but
| just much, much smaller. Very neat!
| LolWolf wrote:
| thanks !
| touchadinosaur wrote:
| Really cool project. I've seen sometimes cheap lab clean outs on
| ebay which can be cool toys, but this is on a different level.
| LolWolf wrote:
| Thanks ! Still need to upload it to Printables etc. Maybe this
| will finally get my ass a bit more into gear.
| alnwlsn wrote:
| Neat. Perhaps one can use it to see PLA creep in real time.
|
| (not a joke, I'd actually like to see that)
| zokier wrote:
| Not creep, but thermal expansion is definitely noticeable with
| interferometry: https://www.youtube.com/watch?v=vupIq4epCQA
| LolWolf wrote:
| yeah, even breathing nearby this thing (or putting a
| soldering iron near the paths) will show a visible change!
| LolWolf wrote:
| Oh absolutely!
|
| I would not actually use this for uhhh, repeatable measurements
| over any extended period of time!
|
| (If that were the case, I'd recommend re-printing it in a
| slightly more stable material, or just CNC milling the mounts
| out of aluminum using some of the ~$1-2K aluminum desktop mills
| and using some aluminum extrusions as the base.)
| ge96 wrote:
| That was a cool physics lab I did (disproving ether) and also
| measuring the speed of light through lucite... other cooler ones
| like helmholtz coils, wax lens focusing microwaves, measuring
| gravity, etc...
|
| Wish we worked on IMUs, I still need to get down quaternions
| adrian_b wrote:
| I wish that humans were not so easily duped into believing that
| things for which someone else uses the same name are really the
| same and things for which someone else uses different names are
| really different.
|
| The Michelson-Morley experiment was indeed very important, but
| it has not proved in any way the non-existence of ether. It has
| just proved that the ether does not behave as it was previously
| supposed, i.e. like the materials with which humans are
| familiar.
|
| It does not matter at all what names are used for it, one may
| choose to name it "ether", "vacuum", "electromagnetic field",
| "force field" or anything else, but all the modern physics,
| since James Clerk Maxwell and William Thomson, is built on the
| assumption that the space is not empty, but it is completely
| filled with something that mediates all the interactions
| between things.
|
| Only before the middle of the 19th century, the dominant
| theories of physics assumed the existence of true vacuum. The
| existence of true vacuum is possible only in the theories based
| on action at a distance, like the Newtonian theory of gravity
| or the electromagnetic theory of Wilhelm Eduard Weber, but not
| in field-based theories, like the electromagnetic theory of
| Maxwell or the gravitational theory of Einstein.
|
| It is rather shameful for physics that the main result of the
| Michelson-Morley experiment has been the replacement of the
| word "ether" by "vacuum", as if a change of name would change
| the thing to which the name is applied, instead of focusing on
| a better understanding of the properties of the thing for which
| the name is used.
| ge96 wrote:
| I thought the whole point was if it did exist the motion goes
| faster in one direction than the other.
|
| edit: not sure if you're referring to dark matter
|
| yeah I gotta read your comment more thoroughly
| SAI_Peregrinus wrote:
| "Ether" is a hypothetical substance with certain properties.
| The Michelson-Morley experiment proved that no substance with
| those properties existed. There's something else with
| different properties, so it makes perfect sense to use a
| different name.
| TeMPOraL wrote:
| In context of approximately everyone's education, the
| history goes like this: in the past people believe there's
| _something_ in empty space, and used the name "ether" for
| that. You learn that, then you learn that MM showed there's
| no "something", no "ether", but that empty space is, in
| fact, empty, which is what "vacuum" means. And then if you
| pay attention or any interest to the topic, you learn that
| there in fact is no pure vacuum, there's always "something"
| in empty space.
|
| The obvious question to ask at this point is, "so ether is
| back on the table?".
|
| Turns out the mistake is, as GP said, thinking MM proved
| space is empty; it only disproved a particular class of
| substances with particular properties. But that's not how
| they tell you about it in school.
| lisper wrote:
| More specifically MM showed that earth is not moving
| relative to a hypothetical medium through which
| electromagnetic waves propagate. So either the universe
| is geocentric or there is no such medium.
| jfengel wrote:
| It's more than just the lack of material. It demonstrates
| that light propagates in a specific way that is different
| from any ordinary material. Light moving in a vacuum is
| different from a baseball moving in a vacuum. The speed
| of light is independent of your own motion, which is not
| true of anything with mass.
| LolWolf wrote:
| Yes! Michelson interferometers are an amazing first lab
| experiment since it teaches you the basics of a bunch more
| techniques which are handy in more advanced experiments, while
| still having a satisfying outcome when done correctly (which is
| not as finicky as other experiments with less fun outcomes).
| zokier wrote:
| > The two beams (split in the beam splitter--the little rectangle
| with a diagonal in the center) add or subtract constructively at
| the output, which yields fringes that are visible to the naked
| eye. These fringes will move as light from one of the arms of the
| interferometer takes a longer or shorter path
|
| This explanation is bit incomplete. If you align the
| interferometer perfectly then it should not have any fringes, the
| fringes indicate that there is some angle between the light
| beams. If you get the interferometer aligned then the beam
| intensity varies as function of the difference of beam path
| lengths.
| LolWolf wrote:
| For sure! I didn't _quite_ want to get into the mechanics of it
| (assuming anyone who is interested would just take a peek at
| the wikipedia or any YT video).
|
| But yes :)
| NetMageSCW wrote:
| I kind of wished there were more details around the tension
| springs and steel rods.
| LolWolf wrote:
| what type of details would you like to see? happy to add more
| if helpful!
| CamperBob2 wrote:
| Over $3K for a similar setup from Thor Labs (1). Wow, you can buy
| everything here _including the 3D printer_ for that. Good work!
|
| 1: https://www.thorlabs.com/michelson-interferometer-
| educationa...
| LolWolf wrote:
| ha, thanks!
|
| that one has uhh substantially less drift for what it's worth,
| but reprinting in more stable material would help that a ton
| (and still be quite cheap!)
| dekhn wrote:
| With products from a vendor like Thor Labs, you're getting a
| lot of quality and knowledge built into the system. Mechanical
| engineers, electrical engineers, optical engineers... all of
| which means an edu kit like that will train a student to be
| useful in most grad research labs (which often build their
| systems out of thor labs components).
|
| It sort of depends on what your goal is; personally, I live to
| see something expensive on Thorlabs, and make a simplified,
| less accurate, and far cheaper alternative in my home lab. But
| that's rarely how folks in labs do it- instead, they will focus
| on getting people to be useful for performing state of the art
| research, which usually depends on applying hundreds of years
| of experience to make some tiny marginal improvement, which
| frequently depends on having extremely precise and accurate
| gear.
| LolWolf wrote:
| Hopefully you enjoyed the post then!
|
| I think there's just such a huge middle ground that's missing
| (for funny historical reasons[1]) between "children's toy"
| and "lab-grade equipment" especially in optics, which is why
| I was excited to make this my first foray into making a fully
| 3d printed "useful-ish" thing that doesn't really exist
| otherwise.
|
| ---
|
| [1] This is because most lab equipment was made _in the lab_
| back in the 60s or so, and having this technical ability was
| a huge advantage for many labs. Now, personnel cost/hours are
| much more expensive relative to equipment, so people will
| pretty much pay whatever to get lab-grade stuff.
| CamperBob2 wrote:
| In some cases, you'll learn more from crappy hardware than
| you will from lab-grade gear. This is probably one of those
| cases. This build will require thoughtful attention and
| debugging/optimization on the student's part in ways that the
| Thor Labs kit might not.
|
| I mean, it's practically the most basic optical experiment
| that you can perform. Nobody needs to pay $3K to learn how an
| interferometer works. It's not a MoT or something exotic like
| that, it's a beam splitter and a couple of mirrors.
|
| Put another way, it's the difference between building a
| Heathkit and putting a bunch of parts together that you
| salvaged from other stuff, for those who are old enough to
| grasp _that_ analogy.
| DoctorOetker wrote:
| you can go much cheaper if you use a microscope slide or similar
| as the "beam splitter". Its not 50/50 so the fringe contrast will
| be lower, but in interferometry one is typically more interested
| in maintaining the position of a peak or number of peaks
| traversed...
|
| alternatively one can use a more grazing sharper angle of
| incidence to bring it closer to 50/50 beam splitting, but then
| the internal reflections become stronger and the setup is no
| longer a nice orthogonal one (but how often is that really
| necessary for a task?)
| LolWolf wrote:
| yeah I cheated a little bit, but
|
| > Ok, time to confess: I did cheat a little in calling it the
| "cheapest" Michelson interferometer, since technically even
| this beam splitter is like 16 USD, but it is very possible to
| use a microscope slide instead at the cost of some contrast,
| which will net out to < 20 cents, even at pretty expensive per-
| unit prices.
|
| :)
| observationist wrote:
| HN hug of death, oh no!
|
| Wayback machine to the rescue:
|
| https://web.archive.org/web/20260109203451/https://guille.si...
|
| Very cool project!
| LolWolf wrote:
| oops! ran out of netlify credits. should be good now !
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