SurprisedPotato t1_jeez2ao wrote

You've noticed that the share price drops by the dividend amount on the ex dividend date. Naturally, because a share that's going to guarantee you $5 if you own it tomorrow is less valuable than one where you have to wait for a year to get the $5.

What you don't see is the gentle pressure pushing the share price up as the year goes by, and next year's dividend date gets closer and closer. A share that guarantees you $5 in a six month's time is worth more than a share that guarantees you $5 in a year's time. When the ex dividend date is only 3 months away it's worth even more.

You won't notice that and can't notice that effect for ordinary shares, because there are so many other factors that affect the share price much more strongly. But you will see this exact effect if you look at the price of exchange-traded fixed income instruments: these are tradable on the exchange but give you literally a fixed amount of cash regularly. The price drops on the ex date, then slowly climbs until the next ex date. You earn the same amount per day no matter how many ex dates you cross.


SurprisedPotato t1_je92k8l wrote

>linear correlation means that the degree difference should be the same, like if the difference between -5 and 5 is ten then the difference in Fahrenheit should also be 10, but it's not, which confuses me severely

Linear correlation means "if you change the °C by 10, then no matter what the original °C was, the °F changes by the same amount (not necessarily 10) each time".

Or, more simply, if you plotted °F against °C, the graph would be a straight line.

The slope of that line doesn't have to be 1.


SurprisedPotato t1_jacqvpl wrote

PEMDAS is a convention, not a fact of mathematics. And it's not the only convention we use, it's just the most common one.

Because PEMDAS is the main convention used, people understand that 5 + 4 x 3 ^ 2 - 1 means "raise 3 to the power of 2, to get 9, then multiply 4 by that, to get 36, then add 5 and 36 to get 41, then subtract 1.

If we used "PEASMD" instead (nobody does), we'd have to write 5 + (4 x 3 ^ 2) - 1 to get the same result.

There are systems that don't need brackets, such as Polish (or Reverse Polish) notation, where you put the operator first (or last) and the things it operates on after that (or before that, for Reverse Polish).

So 4 + 9 would be + 4 9, and the expression I gave above would be

- + 5 x 4 ^ 3 2 1

Which means "subtract the result of + 5 x 4 ^ 3 2 and 1"

+ 5 x 4 ^ 3 2 

would mean "add 5 and the result of x 4 ^ 3 2"

And x 4 ^ 3 2 would mean "multiply 4 and the result of ^ 3 2"

and so on


SurprisedPotato t1_jaan7z1 wrote

I'll think about this. I will note that the Lorentz transformation equations as given in the introduction to this wikipedia page look like they'd work fine, giving non-null answers, in the case v=c. They imply that in the photon frame, only t' = 0 is possible, but that's what you'd expect of a particle not traveling through time. The equations don't say "t' does not exist".

Maybe you've seen a formulation where something is divided by gamma = sqrt(1 - v^2 / c^2 ). Then, certainly, such a formulation might say "such and such a quantity does not exist when v=c". I would suggest that that's a limitation of the formulation, not necessarily a reflection of reality.


SurprisedPotato t1_ja6pztf wrote

For the photon, no time would have passed at all. What that means in practice is that photons can't change as they travel. The photons we receive are exactly the same as the ones that were sent.

Here's another example. Back in the 80's, it was thought that neutrinos were massless, and traveled at the speed of light. Neutrinos are extremely light particles that are emitted from some nuclear reactions - and they come in three "favours".

Also, back in the 80's, careful measurements had been done of the number of neutrinos coming from the sun, and the figure was only about 1/3 of what it should have been.

There were a few ideas proposed to explain that. One was that the sun had switched off and we would all freeze to death within 10000 years or so, but another was that some of the neutrinos from the sun were transmuting into the other forms, and we were only detecting the 1/3 that stayed in their original form. However, if neutrinos were traveling at c, that couldn't happen - if, for the neutrino, no time had passed, then it couldn't transmute, since change needs a passage of time, and for objects at c, no time passes.

Since then, we have confirmed that, in fact, neutrinos do have mass, and don't travel at c, and so time does pass for them on their journey to us from the sun, so we aren't doomed to an icy future. This was very exciting for the physics world, and probably won (or will win) someone a Nobel Prize.

However, for light itself, we know it travels at c, and therefore no time passes for the photons as they cross the 8 light-minutes between the sun and us. (For them, it also seems like no distance has been traversed).


SurprisedPotato t1_j6l3f3t wrote

Our genes contain instructions for making chemicals (proteins) that are used by our body to do stuff.

Our genes come in pairs - each member of a pair is called an "allele", which you can think of as a variant of the gene. Slightly different instructions for the proteins.

In some cases, a phenotype (an external characteristic) is determined by a single gene. Then, as you know, it might be that one allele is "dominant", and an alternative is "recessive". You only need one copy of a dominant allele to "express" that version of the protein, but you need two copies of the recessive one.

Here's one way that might work:

Suppose there's a version of the gene that produces a protein that makes a flower yellow. Without the protein, the flower will be white.

Let's call the allele that produces this protein Y.

Maybe there's a different version of Y which is "broken". The instructions it codes don't make the protein that makes flowers yellow. Maybe they make a protein that does something else, or maybe they make a protein that does nothing at all. Let's call that one y.

A plant might have two copies of Y, or two of y, or one of each.

If it has YY or Yy or yY, it's able to produce the protein, and so it has yellow flowers. The Yy ones might produce less of it, but that doesn't matter of the protein is like an "on/off" switch.

On the other hand, some plants have only yy, which means they can't produce the proteins, and so the flowers end up white.

So Y = "yellow flowers" is dominant, and y = "white flowers" is recessive, because the plant only needs one copy of Y to know how to make the protein that causes flowers to be yellow.


SurprisedPotato t1_j26zgwq wrote

Suppose you are doing research on jelly beans and their effect on acne.

Suppose also there's actually no effect.

A group of scientists does a study, and finds no effect. Since there's no effect, they don't publish their study.

Around the world, maybe many scientists are doing research on the link (if any) between jelly beans and acne. Maybe it's the color? One group studies purple jelly beans, finds no link, and doesn't publish. Another studies red jelly beans, finds no link, and doesn't publish.

Then one day, just by chance, a group found a relationship that was significant at the 5% level.

This was inevitable, since so many groups of scientists are independently studying the phenomenon, in ignorance of what others are doing.

So now there's a published paper linking green jelly beans to acne.

Even more scientists start doing similar research. What other colours have an effect? Do green jelly worms also "cause" acne?

Since there's a lot of research now, more articles get published - red jelly worms are linked to acne, with a p value of 0.02. Green chiffon cake is linked to acne, with a p-value of 0.03. Nobody publishes the results that show no link.

Eventually, the literature shows a strong relationship between confectionery and acne, especially green, especially with gelatin. Food scientists, dermatologists, regulators rely on this information to provide professional advice and to draft laws. It Science journalists inform the public of this new threat to teen health. Soon "everyone knows" how dangerous green food colouring is...

... But actually no link exists.

If people took the time to replicate the studies, and published the failed replications, this wouldn't happen.

Making the initial paper insist on a stricter level of proof doesn't help, because the whole problem is that negative results aren't being published, and the literature is showing a biased set of results. It would be better to publish the results of every study, so people could see whether that 5% result is something that stands alone, suggesting some real link between two things, or if it's just one of a whole series of similar studies, most of which showed no relationship between the things at all.


SurprisedPotato t1_j2302yt wrote

Divorce laws can be complex, and what they say can often seem unfair to one party or other, especially from within the emotional heat of a broken relationship. Some things that can seem unfair, but really aren't:

  • "Wait, they get the kids, AND I have to pay them? I want my kids!". Child support payments are payments to support the child - it is fair that they go to the parent who the child lives with more, and it is fair that they come from the parent who earned more - though this can certainly seem unfair.
  • "I earned that money! Why should they get a share?" The law regards married people as equal partners in a relationship. If one partner quits work to look after the kids, and that means the other can focus on their career, then it is perfectly fair to share the finances equally - or even force the earning partner to provide spousal support while the non-working partner tries the difficult task of getting back into the workforce after a 15 year break - though this can certainly seem unfair.

Divorces are more expensive, and take more lawyer time, when the parties disagree. Since their marriage just broke down, they often are not in the mood to agree on anything much. There'll be a lot of anger and hurt. In the end, both parties will have to agree on something that feels satisfactory to neither, and it can take time to accept that and let the lawyers just do their job. If one partner rants for half an hour to their lawyer about how bad and unreasonable the other partner is, there's no reason the lawyer should not be paid for that time, but yes, it is a waste of money.

If they come before the court and say "here's what we've agreed," that's a lot cheaper than paying a judge, bailiff and both legal teams for the time to argue why the house should be divided 40/60 instead of 50/50. But agreeing beforehand on a painful (for both parties) compromise can be difficult.


SurprisedPotato t1_iy761i2 wrote

That's a goal of some projects, for sure. Already, there are cheapish 3D printers that can print over 90% of their components: often, you need to buy off-the-shelf electronic components to complete it.

> And wouldn’t that destroy the 3D printer industry

Already there are printers on the market where you have a choice of buying a kit and assembling it yourself, or paying more to get it already assembled - or paying less and just getting the electronics (plus a download link for the rest of the parts). Some people are happy enough to assemble their own 3D printer, but if you're just starting our with either 3D printing or electronics, that's a pretty ambitious project. 3D printers can be finicky enough even when assembled by someone who knows what they're doing, let alone by a n00b watching a YouTube video.


SurprisedPotato t1_iugkcbh wrote

Life existed before Oxygen was abundant, so no.

About 2.4 billion years ago, some bacteria figured out how to photosynthesise to get energy from sunlight. Photosynthesis produces Oxygen gas, which they didn't need, so they burped it out. Over hundreds of millions of years, the oxygen built up. Oxygen is quite toxic to life forms not used to it, so that led a mass extinction.

More info: