The metre was originally defined in 1791 (…) as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth’s circumference is approximately 40000 km. en.m.wikipedia.org/wiki/Metre
The kilogram was originally defined in 1795 during the French Revolution as the mass of one litre (1/1000 m³) of water. en.m.wikipedia.org/wiki/Kilogram
… and the last major SI unit is the second which of course you know is (originally was) 1/86400 day.
Please notice about the Celsius scale : the second reference point isn’t a mixture of ice and salt but rather pure water freezing point.
Now how can we as naked humans develop technology to figure this out is something of historical proportion, that’s a quite amazing story !
Can we improve things a bit? Hoping we can get a calendar with no leap year, even number of days in each month, no daylight savings, etc
Edit: obviously no one got what i meant. We can base the day of the year on whatever the fuck you want, but for the love of god can we not split it into twelve randomly numbered chunks, i hate how our months are!!
This would need the Earth to make one complete rotation around the Sun in an exact whole number of times it rotates around itself. …which is not the case right now and extremely difficult (meaning near impossible) to change.
…no daylight savings…
Okay but now we have a greater problem : we have to change (twice, a year) the time when business, school , stores etc… open and close, for it to be convenient with outside natural light. So, in my opinion, this is not an improvement.
Nah fuck it, change something, its all made up anyways!! The whole idea of our “years” doesn’t make any sense on other planets, so we potentially could define some arbitrary system to it.
Not sure if you’re joking or just having a slow day, but neither the length of a day nor the length of a year are arbitrary. One is the length of a revolution of the earth around its own axis, the other is the time the earth takes to complete a full run around the sun. Those two aren’t fully in sync, and to line them up would require a major feat of astroengineering. Given sufficient advances in science, we might get there in a few millennia, if we’re still around by then, but until then leap years are here to stay.
Look, i know what it is based on now, I am saying we should change it. Obviously I am not being super serious, but it would be nice to have even numbers instead of how it is now
There is a calendar that proposes to have 13 months, each with 28 days. That gives you 364 days. Day 365 is new years day and is not part of any month. There are still leap years because as stated, the Earth goes around the sun in 365.24… days. To not need leap years we’d need that to be a whole number.
Well pretty much everyone likes defining a day based on the position of the sun in the sky. While sun rise and sunset might change over the course of the year, nearly everyone agrees that noon is when the sun is the highest in the sky (ignoring day light savings and time zone effects). Turns out people don’t like it when noon occurs in the middle of the night (which would happen if we changes it to any other length of time).
Likewise, nearly everyone has agreed for millenia that a year is defined by earth’s position within its orbit. We know that based on where the stars are at night. Again, people didn’t like having snow during July (which actually happened because the calendar was so far off).
These are not definitions that we can change or have any control over. Additionally, the length of a year (to get earth back to the same spot in its orbit) divided by the length of a day (the time between the sun reaching its apex one day and the next) is not an integer and there’s nothing that says it has to be.
We can’t change it, so if thats important to you, you’ll have to find another planet to live on.
I know what “we like”. I am saying we should change it in a hypothetical post-apocalyptic scenario where humanity joins hands together and demand a yearly calendar that makes more sense. Don’t know why this is getting downvoted, guess you’re all taking me wayy too seriously lol
I’m personally not voting on your comments, but you are probably being down voted because you are either being purposefully ignorant or you are continuing to insist on a “better system” that is physically impossible.
How is a better system impossible? Lets say you are on a star ship, heading away from earth, no reference points besides distant stars. How do you determine time? How do you determine anything? Even if we knew and simulated exactly how fast the earth is spinning and how much it is rotating around the sun, it means nothing out there. We have decided that time works the way it does, all I am asking is to take the extra .24 days in a year and make them disappear. There are several inconvenient ways to do this but it is possible to break it down further so we do not need the extra day. We could round it off to the nearest day every few years, shrug our shoulders and move on with our lives without tacking on another 29th day in some random month? Maybe there is some other way we haven’t thought of? I guess I just thought more people would respond positively to “impossible future scenario where a calendar that makes sense is used” :/
Sure, in that scenario, such a system would be possible. Hopefully, there is still an earth to communicate with however. So we’d have to keep using earth days and years to enable effective communication. Also, the entire ship would have been built using earth based units, so it might be easier to use the system we’ve already got.
We’re not on a space ship though. We’re on Earth, so what happens on this planet matters. You may care more about not having leap years, but the majority of us care about knowing approximately what the weather will look like at a given point in time and how much sunlight to expect, since those things actually affect our daily lives, whereas an extra day in a given month does not.
What about when in the future if we needed to, say, sync time between here and mars, it would make it easier if we had some “frame of reference” outside of the sun maybe. There would basically just need to be a slight redefinition of what a day is, to account for the extra quarter of a day each year, its only a minute each day, ~86,460 seconds in a day instead of 86,400. Not exactly gonna throw the weather/sun off, no?
oh i know the answer. Since a mars day is about 15 minutes longer and out rover there are solar powered it was important that the human operators of them knew what time it was on mars. Nasa’s answer, make a watch that runs about 2% slower. that git the mars watch an extra 15 minutes and so it syncs to the martian sun.
you just have the ship day be the same length as an earth day and start count from day 0. So the ship launches and it clock starts ticking. Now you do need to ask is this going fast enough that time dilation is a thing? That will change how well it can ever sync up to earth.
I really like that one! Guess there’s really no easy way around leap day, but i was thinking you could add an extra ~60.684 seconds to each day and pretend its the same thing? Even increasing the second to be slightly longer could make it possible i think, since we are restarting from scratch it would be easier to adjust it slightly
Your definition of the meter leaves out the most interesting part. Yes, it was 1,000, 000th the distance of the equator to the North Pole, but how far is that? That wasn’t known accurately in the 18th Century. So, two Frenchmen, Delambre and Mechain conducted the longest meridian survey every attempted. They also did so while half of Europe was at war with one another. It was an amazingly dangerous endeavor. There is also significant evidence they totally flubbed and hand-waived their results. So, although their science ended up being questioned, the process and method was accepted and the Meter was defined.
Re Celsius 0 °: the reason I thought perhaps Fahrenheit’s Weird Brine might be a more absolute thing to take de novo temperature from was because I don’t actually know the answer to “how can you ensure water is exactly freezing temperature?” If it’s solid ice it could be colder, if it’s liquid it’s probably warmer, and even if it’s a bucket of cold distilled water with distilled water ice in it, isn’t it still likely hotter than 0 ° C? I feel like there’s probably something involving equilibrium between solid and liquid water that would be difficult to sus out
if you have both liquid and solid water at equilibrium then you have zero degrees Celsius. Pressure has minimal effects …at plus or minus 0.5 atmosphere. of course if you go to a hundred or a thousand atmosphere then there is an effect of pressure.
Small pieces of ice will equilibrate their temperature faster in water.
Surface tension has minimal effect on melting temperature unless you go to extremely small pieces of ice meaning less than one micron, …which is not possible to achieve anyway because such small ice pellet with fuse rapidly to form larger ones.
Yes a bucket of a mixture of small ice pellets, say a few millimeter size, plus water, (this bucket being enveloped with some insulation) would be a great zero degrees Celsius reference point.
… “the actual melting point of ice is very slightly (less than a thousandth of a degree) below 0 °C.” …
isotopic distribution of heavy and light elements in water also has a very slight effect on melting point. So, rainwater and water distilled from ocean will not melt at the (exact) same temperature.
Now, about small particle fusing together this is true not only of ice but of any material.
it’s called sinteringand it is caused by diffusion and a lowering of the surface energy.
This process is faster when the material is near it’s melting temperature and faster yet if in contact with any miscible liquid phase.
Are you asking about how you reinvent the exact same meter? Well that won’t happen. Our units were arbitrary, useful, widely adopted, and then rigorously defined.
The book walks you through it all. You can don’t need to redo civilization exactly the same (the author even suggests some very important things to invent differently, especially in better orders)
That’s a fair point. Most likely if a group of people did some kind of Long Term Naked & Afraid experiment they’d just start with some length of particularly well-crafted cordage, call it a New Meter™ and go from there
Once you can get a good reference for one unit ypu can start to use it to determine the others. None of these are going to be perfectly accurate, but they should be good enough for day-to-day use.
I’d start with time. We’re going to make a sundial. To do this you need to make a drawing compass and some flat ground with plenty of sun. Find a v-shaped stick, or lash a couple together so you can scribe circles in the ground. Start by making one circle around a well marked centre point, then using the same compass, draw another circle centred on the edge of the first. Draw two more circles where the second crosses the first, and two more where those cross it. You should now have a central circle with the perimeter divided into six segments (this is the same technique for drawing a hexagon inside a circle). Put another stick upright in the centre and you have a sundial with 2 hour segments. You can bisect the lines between each of the points to get 1 hour segments, and if it’s big enough, busect again to get 30 minute segments. We’ll get shorter time measurements later.
The next unit to find is the meter. A one meter pendulum completes a swing from one side to the other every second. In order to minimise the effect of air resistance, find a heavy, but not too large rock and tie it to the end of a rope. Measure out approximately out meter of rope (measured from the centre of the rock) and tie it to a solid branch. Next is the tedious bit. Set it swinging as the sundial hits one of it’s marks and count the number of swings until the sundial hits the next mark. You should get 3600 per hour. If you get too many, lengthen the rope and try again, if you get too few, shorten it. Once you have the right number you have both your meter measure and your one second.
You can get a metric tonne, and thereafter a kilogram, by building a balance weigh beam, and a cube shaped container that is exactly one metre on a side. Attach the container to obe side of the beam, and a second container exactly the same distance away from the pivot on the other side. Add rocks to the second container until it balances with the empty first containor. Now fill the first with cold water. Add more weight to the second until it balances again. The additional weight should be exactly one metric tonne. By careful geometry you could reduce tge size of your first container to make this easier, but keeping it big and then dividing the result minimises measurement errors.
Temperature is harder to measure, but you can build a thermometer with any liquid that changes density with temperature. Even water works, although adding alcohol helps I believe. So, while you’re finding the meter, get some fruit and let it ferment. Use the resulting liquid in your thermometer. If you don’t have a glass tube, and can’t make one, use an opaque one, and float a light reed or similar on the liquid, with the end sticking out of the top. Calibrate it with boiling water for 100c, and, assuming a reasonable climate, wrap it against your body for a goid long while to get 37c. If you have accesd to ice, letting it just melt gives you 0c. Dividing the marks you get like this would involve some careful geometric construction, but should yield a usable thermometer. Converting that to Kelvin, as the SI unit, involves adding 273.16.
The ampere and candela are probably of less use in this situation, and are going to be tricky to measure. By assuming gravity is 9.81m/s^2 and using the kilogram you can derive the Newton. From that you have the Joule, and one Joule per second is one Watt. Assuming you build a generator, you can derive the Ampere from it’s older definition relating to the force, in Newtons, between two parallel wires. From there the volt can be derived.
Beyond that, I think you should just hope for rescue!
I hadn’t even thought about getting HH:MM from a sundial, that’s brilliant! Then getting seconds and the meter from a pendulum is just straight up elegant.
By careful geometry you could reduce tge size of your first container to make this easier, but keeping it big and then dividing the result minimises measurement errors.
I thought this was worth a callout for being a really important consideration in this thought experiment. Understanding that larger scale measurements generally reduce error, and perhaps also repetition with averaging of results, would be incredibly useful in fast tracking the redevelopment of precision.
If you have accesd to ice, letting it just melt gives you 0c.
This one I wondered about more because of the effect of atmospheric pressure(?) on melting point, such that I wondered if it would be worth using Fahrenheit’s Weird Brine ice slurry to get ~ -17.778 ° C instead. But that’s ofc also subject to air pressure influencing melting point so I’m unsure if it’d be worthwhile.
Relatively constant 9.81 m/s² gravity is also useful for deriving force as you mention, though it reminds me of learning, to my abject horror, in undergrad physics that gravity does vary quite a bit by geolocation :'D 9.81m/s² is a better starting point than nothing though
This one I wondered about more because of the effect of atmospheric pressure(?) on melting point, such that I wondered if it would be worth using Fahrenheit’s Weird Brine ice slurry to get ~ -17.778 ° C instead. But that’s ofc also subject to air pressure influencing melting point so I’m unsure if it’d be worthwhile.
Varying air pressure is certainly a concern, but repeating the experiment, as you said, would help to reduce the error, as would being as close to sea level as possible. Interestingly, if you have your meter measure you could use that to measure atmospheric pressure by seeing how far you could raise water in a column by suction. At standard atmospheric pressure you should be able to lift fresh water 10.3m.
Relatively constant 9.81 m/s² gravity is also useful for deriving force as you mention, though it reminds me of learning, to my abject horror, in undergrad physics that gravity does vary quite a bit by geolocation :'D 9.81m/s² is a better starting point than nothing though
Gravity is altogether too unreliable and should be abolished. Failing that, You could measure the local gravity by measuring how far a rock falls in a fixed time, say one second, and calculating back from that. If the rock is heavy enough we can ignore air resistance as the effect will be smaller than our measurement error.
Interestingly, if you have your meter measure you could use that to measure atmospheric pressure by seeing how far you could raise water in a column by suction. At standard atmospheric pressure you should be able to lift fresh water 10.3m.
Oh yeah! I should have remembered that actually, since I was just rewatching an episode of that mentions this height limit in the context of vacuum pump history (I think it’s detailed more in season 1 but I forget which episode). So 10.3 m is another key measurement that you want at least one human to have memorized :]
Gravity is altogether too unreliable and should be abolished.
This reads like a Douglas Adams quote and I love it.
I’d start with making a surface plate using Whitworth’s 3 plate method.
Next, make a perfectly square block, pick two opposing faces of that block, that’s your unit of length. Use your surface plate to make more and measure things against it.
If you’re really smart you would have made that block out of some sort of homogeneous material like steel and made it a perfect cube, not just perfectly square. That’s going to be your prototype weight.
Temperature is the easy one, make a thermometer. Mark where the liquid is at based on two different repeatability phenomenons. Subdivide as desired. Someone will come up with a “better” way later.
Time is another easy one, just build a pendulum and start counting.
That sould get you through most of the neo-industrial revolution.
The rest of the base units will come later for now focus on building a lathe.
Fun idea. You mean like the expansion of the universe is going 0.5 light speed at the edge of the void, so the spreading void is basically pulled back right? And then any photons that reached us from just before this void are traveling a tiny bit faster I guess? Being just outside the void?
An explosion wouldn’t change the gravity situation though. Gravitational waves are not relevant here. The danger of an explosion would be the physical matter stripping the atmosphere, and radiation. I think it would take quite a bit longer before Earths gravity is affected significantly based on the drag from traveling through the debris. A gravity well is about the total mass in the center. So wouldn’t a significant amount of material need to make it past the orbit of earth before the orbit is directly altered? The expansion would impact the rotation of matter from the stellar body, but that is not coupled to an orbiting body in a vacuum.
You are right! People often say “what if the sun blew up” in the context of gravity speed vs. light speed thought experiments, but what they really mean is shorthand for what if the entire sun was somehow deleted in a single instant with no trace. But in reality, “blowing up” the sun is much different than “deleting” it and leaves its entire mass behind, just spread around more.
There is even a theorem in general relativity that proves that massenergy cannot be deleted, invalidating a whole swath of such thought experiments. Forgot what it’s called though.
Observation cannot travel faster than the speed of light. No matter what it is you’re using to observe: Photons (light and radiation), measuring gravity, heat, anything. No matter if the phenomenon’s expansion were traveling at the speed of light, the changes to the universe being made as well as our ability to observe them are also traveling at the speed of light.
If the phenomenon were very far away, we would not be able to observe anything it was causing until its leading edge caught up to us. Then we would be destroyed at exactly the same time. This is because in your example it is expanding at exactly the same rate as the universal speed-of-light constraint allows us to receive any indication of its presence. Any evidence of, e.g. a far away star being destroyed would take X amount of time to reach us by its light no longer arriving. However, in that time the edge of the space-destroying phenomenon will also hit us, because it will also take exactly X amount of time to reach us, at the speed of light, from the point where the star was when it was destroyed. The distance is the same, the speed is the same. We would continue to receive light from that star in the meantime, as we already do. (The light from the stars you see in the sky now is already tens/hundreds/thousands/millions/etc. years old depending on the distance to the star in question.)
If the phenomenon were so far away that it is outside of our observable field of the universe, it will never reach us and we will never have any indication of its presence. That’s what “observable universe” means. Anything can happen anywhere outside of the observable universe and it is objectively meaningless to us, because we will never ever be able to reach it, record it, have it influence us in any way. This is, however, predicated on the theory of the perpetually expanding universe being true (which it probably is).
If you want to actually see the stars in your sky winking out over the millennia, I suggest building your universal destruction bomb such that its shockwave travels at, say, half the speed of light or some other suitable fraction.
Thanks, I was having trouble intuitively on that tipping point of expansion moving objects faster than the speed of light and how that is observed without more than lunch napkin level thought. Makes sense. We would never know about or see “the bubble” if it stopped short due to expansion.
The best we can achieve in this thought experiment is to see through a telescope some faraway alien set up a bomb with a countdown timer that will surely blow up at a specific time in the future and destroy the universe, but which we’ll never see count down to zero or explode. If we saw it reach zero it would of course kill us in the same instant as we see it, because by the rules of the thought experiment the explosion travels at the speed of light. But if the alien is far away and the countdown is long enough, the accelerating expansion of the universe due to dark energy will carry it outside of our cosmic event horizon before it explodes.
Using the cosmic comoving distance definition and the cosmology calculator, the last scattering surface of the Cosmic Microwave Background for example is 45.5 GLy away. Its light was emitted 13.7 GY ago (400kY after the Big Bang) at redshift 1100z. I was told that due to accelerating expansion, we will never see galaxies further than 63 GLy away (we don’t see them yet, the matter that we’ll see form them is beyond the CMB sphere for us at present), and if we hopped onto a lightspeed spaceship right now, we can never reach galaxies beyond 17 GLy comoving distance.
So for example if we looked at a galaxy at redshift 3z which is 21 GLy away, and whose light took 11.5 GY to reach us, and saw the alien set up the bomb timer to 11.49 GY, we know that the bomb must have surely exploded by now, but also know that we are safe because it’s far enough away and we’ll never see it explode, even in the infinite future.
Similarly, we can relish the tiny shred of joy in the knowledge that if we did fuck up something really major, like creating a false vacuum bubble in the LHC or whatever, we can never destroy more of the universe than the 17 GLy bubble around us.
If the sphere of destruction is propagating at the speed of light, then any observable effect reaches you at the same time as the sphere itself. Either you don’t observe it because you’re far enough away to be safe, or you don’t observe it because you’re dead the instant it becomes observable.
Incidentally, you might be interested in looking up the idea of false vacuum decay - although if you tend to get anxious about end-of-the-world hypotheticals you might prefer to give it a miss.
Maybe we look at the ratio of country perimeter to area? Counting the number of exclaves could also be a factor. And maybe a ratio of the distance to cover all the exclaves divided by their area?
So if a country were a perfect circle it’s perimeter to area ratio would be 2/r, it has zero exclaves and then it’s width would be the diameter.
If a country were two perfect circles of the same diameter, separated by a distance of the same diameter, it’s area ratio would be 2/r, exclaves would be one, and it’s width would be three times it’s diameter.
So now you can imagine a country like Chile, modeled as a really skinny rectangle, has a pretty large perimeter to area ratio, no exclaves, and a width roughly the length of the rectangle.
I guess you’d have to decide if archipelago nations are measured as the geometry of the sea they own, or as discrete islands.
Thanks for the proposal. That gets us somewhere already, although only for non-landlocked countries. Using the perimeter also opens us up to the coastline paradox.
I guess you’d have to decide if archipelago nations are measured as the geometry of the sea they own, or as discrete islands.
I think that it might serve us better to consider them as distinct islands, to keep the measures comparable with landlocked countries.
You didn’t really mention how this is all being tabulated. Just in theory? Do you have access to data sets or are you making them? The coastline paradox only really exists for smaller and smaller measuring devices. If for example your method is using satellite images of a given resolution, or another consistent measuring tool, the measurements should be comparable between country borders and therefore the error or the paradox should come out in the wash.
I would imagine using some sort of shapefile that I can run calculations in a scripted manner. So, in that case it will depend on the resolution of the shapefile.
I would do perimeter^2/area, to avoid biasing toward small countries. Divide one circular country into two circles with the same total area and p^2/A goes from 4 pi to 8 pi. Divide a square country in two and p^2/A goes from 4 to 6.
I did this all in my head. I think you are right. Point being, small simple algebraic expressions stacked as a a polynomial can be used to create relative scores for this type of analysis.
askscience
Oldest
This magazine is from a federated server and may be incomplete. Browse more on the original instance.