# I'm about to measure the speed of light!!

amolv06
Science 10 Feb '10 20:08
1. 10 Feb '10 20:08
Using a ruler and a stopwatch.

Exciting, I know.

I'll let you know how it goes.

And yes, I know that c is a defined constant, but still, this should be an interesting experiment.
2. PBE6
Bananarama
10 Feb '10 20:12
Originally posted by amolv06
Using a ruler and a stopwatch.

Exciting, I know.

I'll let you know how it goes.

And yes, I know that c is a defined constant, but still, this should be an interesting experiment.
Neat! Let us know how it goes.

(Out of curiosity, how are you going to measure it with a ruler and a stopwatch?)
3. 10 Feb '10 20:23
With a very, very precise stopwatch. I'll post the details some time tonight.
4. 10 Feb '10 20:28
It's 1100 feet per second everyone knows that
5. sonhouse
Fast and Curious
10 Feb '10 21:51
Originally posted by amolv06
With a very, very precise stopwatch. I'll post the details some time tonight.
You better have a stopwatch that can dole out picoseconds. One nanosecond per foot, remember? So having a watch accurate to one nanosecond is no good, you have to have something preferable a thousand times better, at least 100X better, which would be around 10 picoseconds. Even 1 picosecond accuracy would only pin it down to within 99.9%.
6. AThousandYoung
West Coast Rioter
10 Feb '10 22:04
The speed of light is the distance from horizon to horizon (the long way!) divided by the number of hours of darkness. That's how long it takes to go around the world and get back to you.

Yes, the speed of light varies with the season.
7. 10 Feb '10 22:36
We have many different measurements. Believe it or not, we got within ~1% accuracy with a stopwatch accurate to within only 400 picoseconds. We have many plots of data -- the first plot calculates the speed of light to 2.9625*10^9. I can provide more details if wanted later.
8. 11 Feb '10 11:12
My guess is that you could measure the speed of light indirectly, e.g. by looking at interference patterns. I'm not quite sure how, though.
9. 11 Feb '10 11:24
Originally posted by mtthw
My guess is that you could measure the speed of light indirectly, e.g. by looking at interference patterns. I'm not quite sure how, though.
http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment
10. Palynka
Upward Spiral
11 Feb '10 11:51
Originally posted by AThousandYoung
The speed of light is the distance from horizon to horizon (the long way!) divided by the number of hours of darkness. That's how long it takes to go around the world and get back to you.

Yes, the speed of light varies with the season.
I don't get it.
11. 11 Feb '10 16:54
Originally posted by KazetNagorra
http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment
I haven't read the link, so please correct me if I'm wrong, but the Michelson-Morley interferometer was intended to demonstrate "aether" rather than measure the speed of light, correct? By failing, the experiment indicated the constancy of the speed of light, but did not actually measure the speed of light, correct?
12. 14 Feb '10 08:59
Originally posted by Palynka
I don't get it.
he don't get it either, unless he lives on a body massive enough to twirl light around itself.
13. 15 Feb '10 17:13
I like this approach:

http://www.bbc.co.uk/dna/h2g2/A32873493
14. sonhouse
Fast and Curious
17 Feb '10 03:112 edits
Originally posted by mtthw
I like this approach:

http://www.bbc.co.uk/dna/h2g2/A32873493
What is an h2g2 microwave? Did you see that in the piece? Also has an h2g2 kitchen.
Also, if you don't know the frequency of the microwave, you are screwed.

Here is a bit of a wiki article on microwave ovens:

The frequencies used in microwave ovens were chosen based on two constraints. The first is that they should be in one of the industrial, scientific, and medical (ISM) frequency bands set aside for non-communication purposes. Three additional ISM bands exist in the microwave frequencies, but are not used for microwave cooking. Two of them are centered on 5.8 GHz and 24.125 GHz, but are not used for microwave cooking because of the very high cost of power generation at these frequencies. The third, centered on 433.92 MHz, is a narrow band that would require expensive equipment to generate sufficient power without creating interference outside the band, and is only available in some countries. For household purposes, 2.45 GHz has the advantage over 915 MHz in that 915 MHz is only an ISM band in the ITU Region 2 while 2.45 GHz is available worldwide.

So you can have microwaves with three different frequencies and if you arbitrarily pick the wrong one, guess what...

Also, I am an RF guy and wonder how accurate that 2.45 ghz or 915 mhz is in any given oven. Could it go to 2 ghz for instance? If so there is another variable to consider. It would pay to have an accurate frequency counter but that puts it pretty much out of the running for a kitchen experiment, eh.
15. 20 Feb '10 10:11
Originally posted by amolv06
I haven't read the link, so please correct me if I'm wrong, but the Michelson-Morley interferometer was intended to demonstrate "aether" rather than measure the speed of light, correct? By failing, the experiment indicated the constancy of the speed of light, but did not actually measure the speed of light, correct?
Hmm, I think you are correct, yes.