Today I Learned

[Hornbein]

This is why I dislike competitions where we try to evaluate "the best" among people with tenths of a second differences. I'm sure there are better ways to spend our time, energy and resources.

But it's harmless. In this day and age I see this as a major advantage.

 

[pinball1970]

https://phys.org/news/2024-07-lifetime-explosion-star-sky.html

From "the conversation" so I have put it here rather than science sub.

wiki says before August too. https://en.wikipedia.org/wiki/T_Coronae_Borealis

Manchester is pretty rubbish for star gazing so I may have to get to the Pike to see it.

https://en.wikipedia.org/wiki/Hartshead_Pike

 

[fresh_42]

TIL that on March 11, 1978, Claude François died of an electric shock in his Paris apartment when he touched a broken lamp from the bathtub. He was the one who wrote (with Jacques Revaux and Gilles Thibault, the version you know is a cover, translated by Canadian musician Paul Anka) Comme d'Habitude! What a stupid death at 39!

 

[BillTre]

TIL that tree trunk can contain more than a trillion microbes (bacteria and archea, fungi not counted).
Science news article.
biorxiv.

Interesting info bit: trees are estimated to have 450 gigatons of carbon, animals only have about 2 gigatons of carbon.

 

[BillTre]

 

[pinball1970]

T.I.L. NASA's Juno spacecraft captured this color-enhanced view of the giant planet's northern hemisphere May 12, 2024,
https://phys.org/news/2024-07-image-nasa-juno-mission-captures.html

 

[fresh_42]

TIL about FC United Manchester on a TV documentation and a very special dialect.

 

[pinball1970]

TIL about FC United Manchester on a TV documentation and a very special dialect.

Most Man U fans I know supported it. Deep down though? The club is a business and the major share holders sold their stock legally.
The protesters seem to be quieter when we are winning!
Good luck to FC though.
United had the green and gold away kit in 93 worn by Eric Cantona one of my heros.
Beckham took a green and gold scarf off a fan on his return to OT when he was with Madrid.
Stir things up a little!

 

[fresh_42]

Most Man U fans I know supported it. Deep down though? The club is a business and the major share holders sold their stock legally.
The protesters seem to be quieter when we are winning!
Good luck to FC though.
United had the green and gold away kit in 93 worn by Eric Cantona one of my heros.
Beckham took a green and gold scarf off a fan on his return to OT when he was with Madrid.
Stir things up a little!

I liked that one fan was wearing a knit cap with FC St. Pauli printed on it. It is one of our rebel clubs.

 

[DaveC426913]

TIL: how my surveyors laser level can still be used, even though I had given up on it.

It is way too dim to see the beam play across any surface more than 6 feet away during the day, even with the JooJanta 200 goggles that come with it.

But I just had the brilliant inspiration to get a small shiny surface and stick it in the way. The first thing at-hand was a metal pencil case.

The beam can easily be seen ay any point along the entire length of my yard. Had to take a video to capture it, but there it is:

I did some experimentation to see how accurate a level line I could get with the bubble levels.

A mere quarter turn of the adjustment knob offsets the beam by 1/2 inch over 20 feet, and I can easily distinguish a tilt of much less than a quarter turn with the bubble levels. So I think I can get within 1/8 inch over 20 feet.

 

[Ibix]

even with the JooJanta 200 goggles that come with it.

...because the beam is still powerful enough to be perilous? Or because it is no longer powerful enough to be perilous?

 

[BillTre]

 

[OmCheeto]

TIL that 1 in 12 men are colorblind.

 

[docnet]

TIL that 1 in 12 men are colorblind.

https://enchroma.com/

 

[fresh_42]

TIL that and how you can measure c with a microwave and a slice of cheese.

 

[Orodruin]

TIL that and how you can measure c with a microwave and a slice of cheese.

No you can't.

 

[fresh_42]

No you can't.

You can. It only depends on the information your microwave provides.

 

[Orodruin]

You can. It only depends on the information your microwave provides.

No, you can’t. The speed of light is a defined quantity and as such cannot be measured.

At best (assuming the information provided is accurate) you can determine the size of the cheese.

Edit: Or, as I told one of my experimental professors when I was an undergrad and he asked what we had just done (expecting the answer “measured the speed of light”):
- We have checked the calibration of your ruler.

 

[Jonathan Scott]

No, you can’t. The speed of light is a defined quantity and as such cannot be measured.

At best (assuming the information provided is accurate) you can determine the size of the cheese.

Edit: Or, as I told one of my experimental professors when I was an undergrad and he asked what we had just done (expecting the answer “measured the speed of light”):
- We have checked the calibration of your ruler.

I agree that you can't measure c, which is defined, but you can measure the speed of light in a given context, and you would expect to get a value similar to c.

 

[collinsmark]

[...] The speed of light is a defined quantity and as such cannot be measured.

At best (assuming the information provided is accurate) you can determine the size of the cheese.

Edit: Or, as I told one of my experimental professors when I was an undergrad and he asked what we had just done (expecting the answer “measured the speed of light”):
- We have checked the calibration of your ruler.

Technically, this is correct.

[...] It only depends on the information your microwave provides.

This is also correct, in-so-far as the final answer depends on the "frequency" figure typically specified by the microwave oven manufacturer.

 

[Orodruin]

This is also correct, in-so-far as the final answer depends on the "frequency" figure typically specified by the microwave oven manufacturer.

In order to convert that frequency into a speed, you need a distance. A distance that is calibrated by ...

 

[collinsmark]

In order to convert that frequency into a speed, you need a distance. A distance that is calibrated by ...

Correct.

(If you want to "measure" the speed of light, you'll have to pretend the year is before 1983).

 

[Orodruin]

Correct.

(If you want to "measure" the speed of light, you'll have to pretend the year is before 1983).

I mean, you can measure the speed of light if you use units that are not SI units where time and length units are defined in a different manner. However, any such system of units will be less precise than SI units.

 

[fresh_42]

In order to convert that frequency into a speed, you need a distance. A distance that is calibrated by ...

As far as I am concerned, by the length of a piece of metal in Paris.

 

[collinsmark]

As far as I am concerned, by the length of a piece of metal in Paris.

It once was!

But now (assuming SI units), since 1983, the length of a meter is specified by measuring the length that light travels in a vacuum within the timespan of $\frac{1}{299 \ 792 \ 458}$ of a sec.

So today, our system of atomic clocks not only keep official track of time, they also keep track of length too.

 

[fresh_42]

It once was!

But now (assuming SI units), since 1983, the length of a meter is specified by measuring the length that light travels in a vacuum within the timespan of $\frac{1}{299 \ 792 \ 458}$ of a sec.

So today, our system of atomic clocks not only keep official track of time, they also keep track of length too.

I know, but this entire discussion is absurd anyway so referring to the norm meter is as justified as the discussion itself. Nobody would ever actually determine c by a microwave, but it's funny that you can do it with a microwave, a slice of cheese, and a ruler in your kitchen.

 

[OmCheeto]

I know, but this entire discussion is absurd anyway so referring to the norm meter is as justified as the discussion itself. Nobody would ever actually determine c by a microwave, but it's funny that you can do it with a microwave, a slice of cheese, and a ruler in your kitchen.

So when I did this experiment, was I measuring my measuring tape?
Good lord I'm confused.
Btw, I've always heard measuring the speed of light in your microwave involved marshmallows. When did they switch to cheese?

 

[fresh_42]

Btw, I've always heard measuring the speed of light in your microwave involved marshmallows. When did they switch to cheese?

Cheese doesn't explode.

 

[Ibix]

So when I did this experiment, was I measuring my measuring tape?

No. To expand slightly on Orodruin's comment, the meter is defined to be the distance light travels in 1/299,792,458s. So measuring a speed in m/s turns out to be measuring speed in multiples of $c/299792458$. "Measuring $c$" is therefore tautological, give or take your measurement accuracy, and technically sny experiment that does it actually calibrates some combination of the ruler you use and the accuracy of your microwave frequency.

Measuring other speeds (such as the speed of light in a medium) and things like acceleration is not tautological. It's a specific issue with yhe speed $c$.

 

[docnet]

So when I did this experiment, was I measuring my measuring tape?
Good lord I'm confused.
Btw, I've always heard measuring the speed of light in your microwave involved marshmallows. When did they switch to cheese?

 

[jack action]

https://en.wikipedia.org/wiki/Pistol_dueling_at_the_Summer_Olympics​

 

[pinball1970]

TIL that 1 in 12 men are colorblind.

I had the genetics of this wrong for years.

 

[pinball1970]

TIL Limelight actually means light from lime, soda lime that they used to use on the stage.

 

[Hornbein]

TIL Limelight actually means light from lime, soda lime that they used to use on the stage.

Before batteries became a thing bicycle lamps were chemical as well. Carbide I recall.

 

[Ibix]

Before batteries became a thing bicycle lamps were chemical as well. Carbide I recall.

Calcium carbide reacts with water to produce acetylene, which burns, yes.

What happened to the cat who ate calcium carbide? She had a set o' lean kittens. (According to my dad, who had such lamps on his bicycle as a boy.)