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Verifying physics at home

Posted: Mon Mar 25, 2019 11:55 am UTC
by Tub
Let's say you're a die-hard skeptic, and you doubt every experiment that you haven't done yourself. So you set out to re-produce all major experiments at home. I'm wondering, how much of modern physics can be reproduced at home, and on what budget?

I'll skip over newtonian physics because a) a lot of it matches our everyday observations and doesn't require further experiments and b) many of those experiments are cheap and boring.

So let's go straight to the controversial stuff. Sure, you can point to your phone - if the microprocessor in it is working, QM works. If the GPS sensor in it is working, relativity works. But that's not going to satisfy unless you can build your own trusted GPS satellite and your own microprocessors, and neither of those experiments is cheap.

A laser, a mirror and an oscilloscope should be enough to roughly verify the speed of light. If you don't trust the oscilloscope (and can't build your own), a splitter and an interference pattern can also work. Not sure about the cost of the equipment here, but it's possible.

Time dilation is a bit more tricky. The internet tells me that atomic clocks can be bought for as low as $1500. What would you have to do with them to measure a significant clock drift? How long would you have to drive around, or fly via airplane, or how long would you have to leave one on top of a mountain or on the equator or something? Putting one on the ISS or into geostationary orbit would be excellent but costly.

Are there cheaper experiments?

Two slits, a laser pointer and a screen seems easy enough, and there are plenty of guides on the internet. On the other end, verifying the standard model including the higgs boson is going to cost a few billion. Are there any worthwhile experiments in between?

Curvature of earth is simple. The equipment is cheap, your biggest expense is likely travel.

Looking for telescopes, I'm seeing offers for a few hundred bucks that are advertised as strong enough to see planets, so you can verify their existence along with predicted positions and movement. Possibly helpful for relativity if you want to compare different orbital calculations, though I'm not sure if relativistic effects on orbits are large enough.

But backyard telescopes are limited by size, exposure time (you won't have automatic tracking, and wind or seismic activity will eventually be a problem) and atmospheric interferences. Are they useful for mapping the milky way? How about surveying distant galaxies? Measuring the hubble constant? Verifying distant planets? If not, what's the expected budget for something that works?

Another thing is the CMBR. The initial discovery was on some really expensive equipment. How expensive would it be using current technology?

Re: Verifying physics at home

Posted: Mon Mar 25, 2019 2:00 pm UTC
by p1t1o
This is my favorite quantum thingy, and it is experimentally verifiable using fairly simple equipment: ... omb_tester

Re: Verifying physics at home

Posted: Mon Mar 25, 2019 2:12 pm UTC
by Eebster the Great
I don't know how expensive spectroscopic equipment is, but you can learn a lot from that about chemistry and thermodynamics. In particular, if you can see deep UV, you can experimentally corroborate Planck's Law.

If you can analyze gases cryogenically, for instance if you can afford liquid helium, then you can get additional thermodynamic corroboration of quantum mechanics. and the existence of internal degrees of freedom in the nucleus.

For something cheap, polarizing filters are endless fun.

Re: Verifying physics at home

Posted: Mon Mar 25, 2019 4:17 pm UTC
by Nicias
I don't see how this is possible without quantum:

(Three Filter Experiment)

Re: Verifying physics at home

Posted: Mon Mar 25, 2019 4:25 pm UTC
by Meticulac
There's instructions on Instructables for making a spectroscope by using a CD as a diffraction grating, though I'm not sure how well that'd work outside the visible light range.

Re: Verifying physics at home

Posted: Mon Mar 25, 2019 5:22 pm UTC
by DavidSh
As to telescopes, I don't need one to easily see Venus, Mars, Jupiter, and Saturn. Mercury is also a naked-eye object, but since it stays near the Sun in the sky, it's harder to see. If I recall correctly, Kepler's laws were derived from naked-eye observations.
I don't recall clock drives for amateur telescopes being terribly expensive, but it has been quite some time since I last looked for prices for such things.. Last time I looked into astrophotography, people were still using film, and discussing details of hyperring Technical Pan. At the time, for high-quality astrophotos, people were doing some manual guiding to adjust for minor errors in alignment or gearing. Nowadays it should be easy to automate this with a cheap microcomputer system like the Raspberry Pi.

Re: Verifying physics at home

Posted: Mon Mar 25, 2019 11:23 pm UTC
by Heimhenge
I would add the Foucault Pendulum as a great demo of Earth rotation. With a massive enough bob, and a long enough string, you can easily make one that oscillates long enough to show rotation. Did it myself as a science project in a high school gym with an old bowling ball we drilled for an eye hook. Gym was two stories, so maintenance had to attach the suspending string to the rafters. Oscillated for nearly an hour with an initial deflection of around 45°from part way up the bleachers.

Re: Verifying physics at home

Posted: Mon Mar 25, 2019 11:53 pm UTC
by LaserGuy
You can apparently build (or buy) a muon detector for $100 or so, which should allow you to test the time dilation effect by mapping out muon counts at different altitudes.

You can measure cosmological redshifts of objects outside the Milky way (e.g. Quasars) with a good amateur telescope and spectrometer. I found a report of someone detecting gravitational lensing with a 12" telescope (and a 12 hour exposure), and there's been a number of supernova that have been discovered by amateurs. Note that a good amateur telescope (a few thousand dollars or more) should be able to track objects in the sky and do extended exposures, so this isn't really a limitation. Good seeing is really essential though... backyard is not what you want unless you live in the middle of nowhere.

Re: Verifying physics at home

Posted: Tue Mar 26, 2019 11:54 am UTC
by Tub
Thanks for your ideas. Props to Heimhenge for actually doing the experiment! The insights into modern telescopes from DavidSh and LaserGuy are much appreciated; they're a lot more capable than I thought.

re: spectroscopes. I know a couple of chemists, and their equipment is quite expensive. I also work with people doing groundwater management, and our in-situ spectroscopes meant to measure dirt and organic contents (with low accuracy) aren't cheap, either.
Anything you can do with a diffraction grating (or prism) and a consumer camera is possible, i.e. IR and vis at low accuracy with manual calibration. Beyond that, I'm not finding any affordable options right now.

Nicias wrote:(Three Filter Experiment)

Oh wow, I think I finally understood the bell theorem, and why it's a big deal. Thank you!
That being said, to rule out the idea that the filter just "turns" the photon, you need entangled photons instead of stacked filters. And that experiment seems notoriously hard to do. :(

Re: Verifying physics at home

Posted: Tue Mar 26, 2019 1:54 pm UTC
by p1t1o
If using a spectrometer, wouldnt you also have to derive how it works?

If Im doubting any experiment not done by me, then if someone hands me a spectrometer, its just a box with lights on that agrees with what you say.

Sorry, you gotta build a spectrometer. And also prove why it works. Using first principles. If any equipment is needed, you have to repeat for that too.

Foucalt's pendulum is a great idea because proving the underlying principles is relatively simple using straightforward mechanics, which can further be supported with simple observation and measurement.

100.0% skepticism is a difficult thing to live with, should one choose to.

Re: Verifying physics at home

Posted: Tue Mar 26, 2019 2:58 pm UTC
by Tub
Yeah, I almost mentioned that for the atomic clocks. We all know that the illuminati mandate all commercially available atomic clocks to carry GPS sensors and fake a clock drift according to altitude and velocity. Right?

It's not as bad in the case of a spectrometer. You have a black box on your desk and you shine light into it, you can experimentally verify that the output correlates to the input. You can rule out deliberate manipulation by simply not telling the box what it's looking at. If you're super paranoid, you can use filters to measure parts of the spectrum separately.

Re: Verifying physics at home

Posted: Tue Mar 26, 2019 4:53 pm UTC
by PM 2Ring
"Time hacker" Tom Van Baak (& his kids) did an amateur test of gravitational time dilation using caesium atomic clocks on Mt Rainier in 2005, the 100th anniversary of Einstein's first paper on Relativity.


Also see Most Accurate Wristwatch - the first atomic wristwatch. :)

Re: Verifying physics at home

Posted: Tue Mar 26, 2019 9:03 pm UTC
by Eebster the Great
Right, you don't need to personally construct a spectrometer to verify that it works, just shine a bunch of different lights of it with known spectra. For instance, if you shine a red laser on it, you hope the spectrometer only reports receiving monochromatic red light, or something is up.

Re: Verifying physics at home

Posted: Wed Mar 27, 2019 8:16 pm UTC
by Lothario O'Leary
Really the big problem is, how does one verify that a laser works? I'm not aware of any method to produce a laser at home.

Re: Verifying physics at home

Posted: Wed Mar 27, 2019 9:16 pm UTC
by Heimhenge
Lothario O'Leary wrote:Really the big problem is, how does one verify that a laser works? I'm not aware of any method to produce a laser at home.

Not really a laser, but a bright source of white light (say, an arc lamp), a prism, a small aperture, a collimating lens, and you've got a monochromatic enough source of light. That's all you'd really need to run Eebster's test.

Re: Verifying physics at home

Posted: Wed Mar 27, 2019 11:27 pm UTC
by Eebster the Great
Filter paper is also cheap and produces fairly monochrome light. But even with the laser, you can confirm with your eyes that the light is red, and that's a source of red light you might already have around. The idea is to look at things of known color with the spectrometer to verify that its results are consistent with what you already know.