Recent comments in /f/explainlikeimfive

GrumpyOldLadyTech t1_iugix60 wrote

Reply to eli5 - If our cells only turn a certain amount of times before we die. Does causing micro damage from resistance training shorten our lifespan? by aus_ben93

The way DNA replicates to termination is a little different than just apoptosis. Let's see if I can explain.

Cells have a natural life cycle, and when they age out, they have a natural self-termination called apoptosis. This is built into the structures and has a set timeline. If you're talking about cells that aren't manufactured somewhere like blood cells in marrow, they replicate via mitosis and just keep going.

However! Oxidative damage to the telomares shortens the terminus of the DNA. This is directly related to the effects of aging and age-related changes. This happens on a molecular level.

What you're describing happens at a cellular level, and the body has systems in place to account for that (for the most part). You're not prematurely aging yourself by working out. If anything, you're keeping your systems stimulated to keep up on cellular "housekeeping," to include removal of dead or dying cells more appropriately.

... in short, you're fine!

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breckenridgeback t1_iugi5r5 wrote

Reply to comment by tdscanuck in ELI5: How do plants know that they will be eaten and therefore their seeds will be spread and regrow? by HazeThere

> there is nothing in the universe that says "there should be capsaicin".

There's nothing in the Universe that says "there should be capsaicin" specifically. But conditional on animals having particular receptors, there is something that says "plants with it can outcompete plants that don't".

Yes, evolution has (significant) random elements in terms of where you start on the fitness landscape and in terms of non-biological factors (e.g. "oh shit a meteor just hit the Earth) that can sometimes intervene. But evolution is tightly intertwined with game theory, and it isn't a coincidence that game-theoretic strategies show up all the time in evolutionary biology.

"Organisms, broadly speaking, will eat and reproduce" is just as iron-clad a law of our Universe as "objects will roll downhill" is. Maybe more so, since it's implied by abstract mathematical law and not even by the particular quirks of actual physics.

> There are, for all practical purposes, infinitely more traits that have never and will never be expressed than ones that we've ever seen.

This is true to some extent, but the frequency of convergent evolution shows us that some patterns really are just super useful. Wings have evolved independently in birds, insects, mammals, and even plants if you count the little fins on a maple leaf. That's not a coincidence.

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dlbpeon t1_iugh9y2 wrote

Reply to ELI5 How did knights participate in tournaments like jousting without killing themselves? by QuantumHamster

If you were rich and could afford heavy armor, you were ok. If you were poorer and had cheap armor, you might get injured. Freak accidents did happen that would cause death, but unlike GOT would have you believe, most Knights went uninjured. Just like modern-day Bull Riders, you can make the sport safer, but there is always risk involved.

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tdscanuck t1_iuggzo2 wrote

Reply to comment by breckenridgeback in ELI5: How do plants know that they will be eaten and therefore their seeds will be spread and regrow? by HazeThere

There are physical laws that dictate why a water droplet takes the shape it does; there is *nothing* in the universe that says "there should be capsaicin". If the capsaicin mutation hadn't happened the entire ecosystem would have been just fine without it. There are, for all practical purposes, infinitely more traits that have never and will never be expressed than ones that we've ever seen.

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EvenSpoonier t1_iuggs4f wrote

Reply to ELI5: How do plants know that they will be eaten and therefore their seeds will be spread and regrow? by HazeThere

Although some people out there on the fringe of what we call knowledge have speculted about possible consciousnesss in plants, it's generally thought that plants don't know anything, at least not in the way we think about what it means to know something.

Evolution has only one rule: whoever dies with the most grandchildren wins. Plants don't seem to have "known" to be sweet or spicy or anything else. It just happened that the sweetest plants got spread the most, and (mostly) passed the things that made them so sweet on to their children. Do this enough times, and the whole species starts to taste sweeter. It's not exactly an accident -there are systems by which it works, and those systems can be used to predict how things are likely to go in the future- but as far as we can tell there is no mind behind it. It just worked, and so it kept on working.

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breckenridgeback t1_iuggmjc wrote

Reply to comment by tdscanuck in ELI5: How do plants know that they will be eaten and therefore their seeds will be spread and regrow? by HazeThere

"Just an accident" is maybe not giving credit to the forces involved here.

The plant itself isn't intelligent, but the process that makes it kind of is (in the sense that there is meaningful information encoded in which individuals reproduce or not). It isn't a coincidence that a chili pepper produces capsaicin any more than it's a coincidence that a water droplet takes a spherical shape: both are obeying mathematical laws, just not with any "intent" behind them.

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tdscanuck t1_iuggcpd wrote

Reply to ELI5: How do plants know that they will be eaten and therefore their seeds will be spread and regrow? by HazeThere

They dont know. They didn't plan any of it. It's just an accident.

That basically how evolution works...plants & animals keep randomly trying things (DNA mutations)...some of them work to make the critter more successful, most don't work at all and the critter dies.

Every once in a while, a mutation is useful enough that the critter gets to reproduce more, creating more critters with that mutation. Eventually, the traits that don't work die out and the ones that do work well (enough) spread.

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jourmungandr t1_iugg885 wrote

Reply to ELi5: Why specifically is it oxygen that is required for life? by West_Theory3934

Aerobic respiration releases about 10x more energy than anaerobic respiration from the same energy sources. Oxygen is one of the best oxidizers that is commonly available which is why it's able to do that. There are much stronger oxidizers known to chemistry which could release even more energy. However if you get much stronger than oxygen they start reacting so easily with other things, those chemicals would destroy all the other molecules that make up an organism.

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Chromotron t1_iugg3u3 wrote

Reply to ELI5: Why do we have real numbers with one term, complex numbers with two terms, quaternions with four terms, octonions and so on, and nothing in between? by wah_bsdk

First, there is not really a "and so on". It depends on what you allow, but it ends as soon as you add some common requirements. We often encounter:

  • the reals ℝ, an (actually, the archimedean complete) ordered field, i.e. we have ≤ and it is compatible in various way with + and ·,
  • the complex numbers ℂ, an (algebraically closed, complete) commutative division algebra, i.e. a·b = b·a holds,
  • the quaternions ℍ, an associative division algebra, i.e. a·(b·c) = (a·b)·c holds,
  • the octonions 𝕆, an alternative division algebra, i.e. a·(a·b) = (a·a)·b and a·(b·b) = (a·b)·b hold
  • the sedenions 𝕊, which are not even a division algebra, i.e. for some x there is no y with x·y = 1; they at least still satisfy a·(a·a) = (a·a)·a and (a·a)·(a·a) = ((a·a)·a)·a.

The cursive words are the most important aspect here: each of them is also true for the ones above them, but not below. At each step, something is lost.

With 𝕊, almost none of the typically used properties are left, we barely(!) can define powers x^n without having to write down in which order we multiply them. Most people hence stop the list there, only very few people seriously work with them.

Generally, classification theorems exist for algebras over the reals, which say that the dimensions 1, 2, 4, 8 are the only ones where algebras with the above properties exist. However, depending on what exactly you require, it is not always true that the above list contains all such algebras; only the dimensions are certain powers of 2!

For convenience, I will now write "ℝ-algebra" for what is typically called a "unitary finite dimensional algebra over ℝ": a set A with addition + and multiplication · containing (and compatible with) ℝ, satisfying:

  • distributivity (that is: a·(b+c) = a·b+a·c and (a+b)·c = a·c+b·c) for any a,b,c in A,
  • commutativity of addition (a+b = b+a),
  • centrality of ℝ (s·a = a·s for all a in A and s in ℝ, in other words, multiplication of two numbers is commutative if at least one factor is in ℝ)
  • negativity (a+(-1)·a = 0, noting that -1 as a real number is in A),
  • addition&multiplication turn A into a real vector space of finite dimension dim(A) (there is a finite list a1, a2, ..., an of elements of A such that every element of A can be written in the form s1·a1 + s2·a2 + ... + sn·an for suitable s1, s2, ..., sn in ℝ).

If you then require that A satisfies some sane other properties, e.g. allowing division, or associativity or commutativity, then one can show that only very few examples exist. The exact version depends on what you want, there are many different results.

Lets maybe dive a bit into one such result by Hurwitz on "composition algebras", where the standard absolute value |·| on ℝ extends linearly to the algebra and furthermore satisfies |x·y| = |x|·|y|. Then such algebras exist only in dimensions 1, 2, 4 and 8. Some examples are

  • ℝ,
  • ℂ, with |a+bi|² = a²+b²,
  • ℍ, with |a+bi+cj+dk|² = a²+b²+c²+d²,
  • 𝕆 with the same, but 8 terms.
  • ℝ², with |(a,b)| = a²-b²,
  • and many more.

Note that the last one is not on the list above, and there are similar examples of dimensions 4 and 8.

But the really interesting part about this theorem is that |x·y| = |x|·|y| on ℂ corresponds, with x = a+bi and y = c+di, to the formula (a²+b²)·(c²+d²) = (ac-bd)²+(ad+bc)², hence a product of two sums of two squares is again a sum of two squares! And we can verify this formula directly, never even talking about complex numbers, or even composition algebras; it actually holds in any ring! Similarly, we get such formulas for sums of 4 or 8 squares by invoking ℍ or 𝕆, they are just a bit longer.

Yet, almost magically, there cannot be such a formula for other numbers of variables by the theorem!

Lastly, a quick statement on the proof behind such results:

  • Proving that ℝ is the only archimedean ordered complete field is typically done in the first year of a calculus course and not difficult, just a bit technical.
  • The only ℝ-algebra (except ℝ itself) that also happens to be a field is ℂ, as follows from the fundamental theorem of algebra (i.e. that every non-constant polynomial with complex coefficients has a root within ℂ); this famous result is shown similarly early when studying mathematics.
  • There is a very vast theory of "Brauer groups" that classifies, for any field K, all the K-algebras that also happen to be division rings (similar to fields, but without requiring commutativity). For K=ℝ, the only examples are ℝ, ℂ and ℍ. This is already pretty advanced, typically a Master's course, and often done when also dealing with "Group/Galois cohomology".
  • Almost all proofs where the answer is either 1, 2, 4, 8 or exactly the list ℝ, ℂ, ℍ, 𝕆 are seriously involved and usually done by invoking advanced methods from algebraic topology such as K-theory or higher homotopy groups. Even sketching anything here would go way beyond this already long post.

Edit: forgot to mention:

Those results on composition / division algebras also have ramifications on very different looking things that are quite interesting in their own rights, such as:

  • "Sphere eversions" (turning a sphere inside-out without creasing or tearing it) exists for spheres of dimensions 0, 2 and 6 within 1, 3 and 7 dimensional space, respectively. There are some nice videos of the 2-sphere being everted in 3-space such as https://www.youtube.com/watch?v=OI-To1eUtuU&t=1131s, and I would recommend the entire video as worth your time.
  • A "cross product" exists only in dimensions 0, 1, 3 and 7. The 3-dimensional one is widely known among multiple fields and is related to quaternions, but the 7-dimensional cross product coming from octonions is something even many mathematics professors don't know.
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