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Ask HN: What is a science fact that blew your mind when you learned it?
I'll go first. When I read that it takes a photon over 100,000 years to exit the Sun as visible light, I was completely astounded. Curious what other insights from science people have learned that were completely unexpected to them.
- shansense 6y agoThat the Amazon soil is actually very poor in nutrients and the dust from the Sahara desert is actually what keeps the Amazon rainforest alive. Long ago the South American and African continents were one. To think of it, there is still a major connection!
- gadders 6y agoObvious when you think about it, but I didn't realise for ages that all the planets orbit in the same plane.
- riffraff 6y agoRelated: I was mind blown when I realized this is true for the pretty obvious reason that the various orbits "averaged" out.
- sloaken 6y agoIs the obvious reason because the sun is spinning? Or some other not so obvious reason I do not know of?
- gadders 6y agoWell this may not be correct, but I'm assuming the plane they spin in is the same as the equator of the Sun and in the same direction as the Sun's rotation. That would make sense if they were made of "stuff" that was thrown out from the centre and clumped together.
- fragmede 6y agoPluto does not orbit in the same plane - it is about 17° off. HOWEVER! Pluto is no longer considered a planet, making this science fact true. (It is now considered a dwarf planet instead).
- scott31 6y agoAverage density of the universe is about 1 proton mass per cubic meter
- pyfgcrl123 6y agoThat's including dark matter, I think? With just the matter we can see, it's not even that.
- loandigger 6y agoThe dual slit experiment. Run the experiment with no one watching it, it produces result A. Run it again and watch it, it produces result B. Watching the experiment changes the result. WTF????
- dilippkumar 6y agoThe dual slit experiment produces different results? I must be thinking of something else - I thought that electrons passing through a dual slit always produce an interference pattern. Anyone got a link?
- rootbear 6y agoThere is a long Wikipedia article at https://en.wikipedia.org/wiki/Double-slit_experiment https://en.wikipedia.org/wiki/Double-slit_experiment The most mind boggling aspect of this for me is the single photon version, which is under the "Interference of individual particles" section of the above article. The point is that you get an interference pattern even when only a single photon at a time is sent through the slits!
- Gibbon1 6y agoYeah this is the point where you stare down into the rabbit hole.
- drran 6y agoIt's false information. It's debunked multiple times. "Watching" means "placing or turning on an additional detector", which ruins interference pattern. To develop intuition, look at double slit experiment made at macro scale using walking droplet.
- JohnDeHope 6y agoI'd really appreciate a few links to this. I am on a youtube binge lately watching quantum dynamics lectures for lay people. The constant talk about "watching" and "observers" drives me crazy. I refuse to believe anything has anything to do with whether or not anybody is "watching" anything. Bouncing photons off of it? Sure I can see how that would affect all sorts of things. But if the bouncing photons alter what's going on (and it seems they cause as much quantum decoherence as anything else might) then that's not the same thing as just "watching". That word implies to me "there are ambient photons or some other field or background that does not alter the experiment, and I am merely observing that background to get an idea what's going on within the experiment". If the experiment cannot be conducted without interference within an ambient background of photons flying around, or within some other medium we passively non-destructively-to-the-experiment observe, then we cannot currently be said to be "observing" anything at all with respect to that experiment. Let's just say that, can't we? If we can't not alter the relevant circumstances of what's going on, then let's just admit that, without using faulty and improper language to "describe" what's happening. Can somebody help me out with this?
- znpy 6y agowe can see our nose all the time, but our brain filters it out. if you close one eye and keep the other open you'll suddenly see one side of your nose.
- dave_sid 6y agoI can see my nose now
- mistersquid 6y agoGot your nose!
- krapp 6y agoWe also have a blind spot in each eye where our optic nerve passes through our retina, which the brain constantly edits out.
- akmarinov 6y agoAlso while turning your head you don’t really see, but your brain pieces things together and plays an image of what it thinks you should see.
- posterboy 6y ago> Can explain Quantum gravity > Can explain DNA ... > Can see his own nose
- kpwags 6y agoThat when we look up at distant stars, nebulas, & galaxies and the like...we are looking back in time. What we see could have been gone for decades, centuries, or longer.
- m463 6y agoSort of similar to tree rings and even... dirt. We could probably dig in our backyards and find artifacts of 10,000 year old life. We are transient.
- perardi 6y ago“longer” is an understatement. The Andromeda galaxy, which is viewable by the naked eye, is 2.5 million lightyears away. And that’s the closest galaxy to us. https://en.wikipedia.org/wiki/Andromeda_Galaxy https://en.wikipedia.org/wiki/Andromeda_Galaxy
- pyfgcrl123 6y agoOne of the closest, anyway. Yeah, most distant objects observed are over 10 billion years "in the past".
- ffpip 6y agoNot science, but Mathematics - That there are more ways to arrange a deck of 52 cards than seconds that have elapsed since the big bang took place. Thousands of similar questions on reddit for anyone interested- https://duckduckgo.com/?t=ffab&q=science+fact+site%3Areddit.com%2Fr%2Faskreddit https://duckduckgo.com/?t=ffab&q=science+fact+site%3Areddit....
- akmarinov 6y agoAlso chances are that no one has shuffled a deck in the same order as someone else has, ever in history.
- edanm 6y agoThis one gets me too. It's so counterintuitive to me. (Caveat: this is assuming people shuffle well, which of course most people don't, therefore in fact people probably have shuffled to the same state).
- pks016 6y agoFrom last few days I have been watching cards videos from numberphile. It's so fun and interesting.
- throwaway590007 6y agoEvolution is dominated by genetic drift, not natural selection, most of our genomes are junk, and we are in fact not very optimally adapted to our environments The microbiome affects the brain, the immune system and is involved in multiple psychiatric/behavioral conditions The identical ancestors point (in short, everyone is a descendant of everyone who ever lived approx 7000 years ago) Mosaicism and chimerism - it's not clear "who we are" and it's not even "our genes" Cancer behaves as though it were a living being of its own, there's evidence it could be a form of regression to unicellular lifeforms, and what's more it does have a microbiome of its own
- ampdepolymerase 6y agoMost of the facts stated are inaccurate, or at least phrased incorrectly in a pop science manner. What you have written are technical subtleties, not the main ideas that undergird biology. Biology is not an absolute hard science, but it serves nobody to emphasize and blow up the details while rejecting the core ideas completely. For example, if I tell a novice programmer that JavaScript is a compiled language like C, that is a very inaccurate statement. The subtleties of JIT interpreters can be clarified when you already have a clear understanding of the differences between an AOT compiler and a high level interpreter. HN is predominantly filled with people of math and computer science background. Those 'facts' in your comment are at best misleading if you do not already have strong grasp of the central dogma.
- throwaway590007 6y agoAlright then, let's see you phrase it better instead of just flagging my post with no justification other than a condescending dismissal. At what point did I reject the core ideas though? And what does any of what I said have to do with the central dogma?
- hbcondo714 6y agoGrowing up, I was taught that the main reason why it's bad to drink is because it kills brain cells and brain cells don't grow back. Apparently that is not the case anymore: https://www.scientificamerican.com/article/the-adult-brain-does-grow-new-neurons-after-all-study-says/ https://www.scientificamerican.com/article/the-adult-brain-d...
- adsjhdashkj 6y agoWhat level of drinking would cause this, though?
- berbec 6y agoCome over to my house and I'll show you... That's why haven't had a drink for the last 5 years
- adsjhdashkj 6y agoWell, i just meant i had not heard this - so i was curious if a glass of wine a night causes damage.
- m463 6y agoIt's exercise that causes the brain growth. (the famous rat experiment with the "stimulating environment" and brain grown was later attributed to the exercise wheel)
- thedevindevops 6y agoThe 100-step rule in neuroscience, that states that no primary brain operation (e.g., face recognition) can take more than 100 neuron firing “steps.” (Feldman & Ballard, 1982)
- lazyjones 6y agoThis is a bit misleading since there are way more steps / neuron firings involved, the rule just says that these operations happen in less than 500ms and 1 firing per 5ms is the maximum throughput of a single neuron. These brain operations aren't implemented as a sequential chain of neuron activations though.
- lazyjones 6y agoA 2016 poll of 1,500 scientists reported that 70% of them had failed to reproduce at least one other scientist's experiment (50% had failed to reproduce one of their own experiments).
- RhysU 6y agoI would love to see this number for computational scientists.
- aewens 6y agoWhile anecdotal, its easy to run into issues like this[0] where scientist with little CS background assume certain behaviors in code that don't actually exist. [0] https://www.vice.com/en_us/article/zmjwda/a-code-glitch-may-have-caused-errors-in-more-than-100-published-studies https://www.vice.com/en_us/article/zmjwda/a-code-glitch-may-...
- Fragoel2 6y agoI don't have a clear reference to point you to but in many CS research fields these number are equally bad. Often code is not even published and is a complete mess when it is.
- fiftyacorn 6y agoReminds me of doing chemistry labs at uni. You follow the experiment plan and get nothing like the expected result so you add big error bars and your result matches. i remember getting a clear linear relationship once that as supposed to be a curve. Solution was error bars and a curve to match expectation. Pointless
- ManuelKiessling 6y agoNot a fact per se, but: the sheer amount of living things that came before me, in the sense of my direct ancestors and their direct ancestors etc. etc – not only my human ancestors, but the whole of my ancestors all the way back to the origins of life itself – and I would not be here today if even one of them would have died before reproducing... that manages to blow my mind every single time I think about it.
- tunesmith 6y agoAnd it can be reeeeally depressing to think about for those that aren't having children.
- Geee 6y agoTry counting the total number of your ancestors: you have 2 parents, they have 4 parents in total etc., i.e. 2^N where N is the number of generations. Going just 40 generations back (about 1000 years), you had 2^40 = 1,099,511,627,776 ancestors.
- AnimalMuppet 6y agoBut not necessarily 2^40 unique ancestors. That is, the same person may be your ancestor by more than one route through the subsequent generations.
- raint 6y agoThe physics & biology behind eyesight. Our eyes collect light that is "left over"(not reflected) from other surfaces. Can't explain why but I had always had a sense that objects somehow emanated their own "image". Learning that colors manifest themselves because every other wavelength was absorbed was fascinating.
- sieste 6y agoThat there is such a thing as deterministic chaos (aka the butterfly effect), ie. infinitesimal perturbations can quickly produce macroscopic changes, and all the philosophical implications that result from it. That despite the apparent complexity of the weather many atmospheric phenomena can be explained from first principles with pen and paper calculations. That the existence of elementary particles can be derived from simple symmetry considerations (That one blows my mind every time.) That when we look out into the universe we see elements roughly in the same proportions as they appear on earth. (We are all made out of star dust!)
- Chris2048 6y agoIsn't that just probability distributions?
- fsflover 6y agoMany statements here: https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future
- blablabla123 6y ago> which states that entropy, or a loss of the energy available to do work, must rise over time.[2] Stars will eventually exhaust their supply of hydrogen fuel and burn out. Since entropy is a statistical quantity, the second law of thermodynamics is a statistical statement. And because modern physics essentially deals with Hamiltonian systems, it can be proven that a time exists when entropy goes down again. The intuitive proof is really nice. Since energy is conserved, one can imagine the global state (position, momentum) as position in a park covered in snow. So someone walking through it will eventually walk over his own footsteps. Not precisely but it's arbitrarily close, the longer one waits. https://en.wikipedia.org/wiki/Poincaré_recurrence_theorem https://en.wikipedia.org/wiki/Poincaré_recurrence_theorem I really like that theorem
- cbsks 6y agoI think "mind blown" is an accurate description when I first saw the Hubble Deep Field image: https://hubblesite.org/contents/articles/hubble-deep-fields https://hubblesite.org/contents/articles/hubble-deep-fields I already knew that "the universe is incomprehensibly large", but seeing how many entire galaxies there were in a random dark patch of sky was eye opening to me.
- perk 6y agoDon't know exactly why, but thinking about the vastness of the universe always cheers me up. Thanks for sharing :)
- milkytron 6y agoAs a kid, it used to weird me out to the point where I would forget what I was doing, get the chills, and enter a sort of trance. It never impacted me negatively, but pondering the scale of everything and how little of an impact we have on the grand scheme of the universe gave me a weird sensation.
- take_a_breath 6y agoRelatedly, my dad always told me that thinking about the vastness of the universe "weirded him out." My hypothesis is that he has narcissistic tendencies so pondering the vastness of the universe only highlights his own insignificance. I've noticed similar reaction from people who visit a large city for the first time and get a sense of how small they are in the grand scheme.
- tfandango 6y agoReminds me of the Total Perspective Vortex from Hitchhikers Guide to the Galaxy, which exposed an individual's insignificance in the universe.
- shaftway 6y agoIt makes me sad. Born too late to explore the world; born too early to live forever and explore the entire universe; born just in time to make dank memes.
- Liquidity 6y agoWhen i could "see" my visual blindspot. https://lasikofnv.com/try-these-3-fun-tests-to-find-your-visual-blind-spot/#:~:text=Position%20your%20head%20to%20look,with%20the%20surrounding%20yellow%20color https://lasikofnv.com/try-these-3-fun-tests-to-find-your-vis....
- captn3m0 6y agosomewhat related, I was so glad when I found out the reason behind a dim bulb that's just turned off appearing brighter when _you look away_. The answer is in the density of rod cells (which are photon receptors of the eye that specialize in low-light) are concentrated on the outer edges of the retina. So if you look straight at a dim bulb - the photons hit the cone cells, which aren't sensitive enough, but if you look away, the photons hit the rod cells and you can see the bulb!
- sloaken 6y agoOMG me too. I was having an eye exam. The technician had a black field with a bunch of lines. Holding a rod with a white dot, and told to let them know when it disappeared. I laughed, "Well that will only happen if you put it behind your back." They laughed, "Everyone has an astigmatism where the nerves enter the eye. We are looking for that or any other issues." I was so shocked when the dot disappeared. Also happy to hear it was the normal blind spot.
- m463 6y agoThere is one driving your car too. :)
- moistly 6y agoNot if your mirrors are set correctly. Lean your head to the side window, set the mirror so that it just misses the tail end of your car. Position your head over the centre console, set the mirror. There is now approximately no blind spot. You can fine-tune by careful observation on a multi-lane highway as people pass/you pass others. Done correctly, there is no blind spot.
- tito 6y agoA gallon of gasoline creates 20 pounds of carbon dioxide. So my trip to the grocery store could be adding as much carbon dioxide to the air as the groceries I pick up!
- m463 6y agoThat is fascinating. A gallon of gasoline weighs 6 pounds, so it probably must be using 14 pounds of oxygen.
- NoOneNew 6y agoLet me add on. Your average big tree (oak, pine, maple, etc) after about 10 years of age, collect about 40 pounds of carbon dioxide every year. Again, averages, there are plenty of factors. I use that as a way to visualize the problem with "a solution".
- rootbear 6y agoI was pretty amazed by the Casimir Effect when I first learned of it. https://en.wikipedia.org/wiki/Casimir_effect
- m463 6y agoI think I need to get an advanced degree just to be able to read that wikipedia entry.
- proactivesvcs 6y agoHow prion diseases work and spread. They're basically infectious lego. You may not thank me if you read about them...
- pier25 6y agoGravity is not really a force or objects "attracting" themselves but a consequence of the curvature of spacetime. At least that's my pedestrian interpretation :)
- drran 6y agoWhat releases energy then, when objects are accelerated towards each other?
- Xcelerate 6y agoA compressed spring weighs more than the same spring uncompressed. The moon and earth weigh less together than if you weighed them separately and added the values together. Most of the weight of solid objects is due to the high speeds and binding energies of the elementary particles within them rather than the rest mass of the constituent particles. The number of particles that exist is relative to how fast you are accelerating. Everything that has energy (which is everything we know of) affects the gravitational field; this means that even photons are "attracted" to each other. A non-relativistic quantum state will return arbitrarily close to its initial state an infinite number of times. There is such a thing as interaction-free measurements: you can take photos of things without ever letting light hit a detector and you can tell whether a bomb is "active" without actually interacting with the detonator. Energy is just a number that is calculated as a function of the state of a closed system — that this number is a constant results from the time transitional invariance of the laws of physics. Similarly, conservation of momentum is due to the spatial invariance of the laws of physics, and conservation of angular momentum is due to rotational invariance. Also, conservation of energy does not hold under general relativity.
- iheartblocks 6y ago> There is such a thing as interaction-free measurements: you can take photos of things without ever letting light hit a detector and you can tell whether a bomb is "active" without actually interacting with the detonator. Can you provide a link that talks about that? It goes against my understanding of why there's an uncertainty principle at all
- AnotherGoodName 6y ago>Most of the weight of solid objects is due to the high speeds of the elementary particles within them rather than the rest mass of the constituent particles. Wait i agree energy is mass but is this specifically correct? The rest mass is always much higher when i've seen it in equations.
- Xcelerate 6y agoWhoops, I forgot binding energy. But yes, rest mass of quarks is only about 1% of a proton or neutron’s mass.
- arkanciscan 6y agoThat mitochondria have their own DNA and used to be separate organisms. Or when I heard that trees feed each other and fungi through their roots.
- CrazedGeek 6y agoThe life cycle of the lancet river fluke: https://www.damninteresting.com/a-fluke-of-nature/ https://www.damninteresting.com/a-fluke-of-nature/
- deleted 6y ago[deleted]
- Stratoscope 6y agoElectrons in a copper wire do not travel at the speed of electricity. Not even close. Electricity travels at nearly the speed of light. Electrons themselves travel like molasses: "In the case of a 12 gauge copper wire carrying 10 amperes of current (typical of home wiring), the individual electrons only move about 0.02 cm per sec or 1.2 inches per minute (in science this is called the drift velocity of the electrons.). If this is the situation in nature, why do the lights come on so quickly [when you flip the switch]? At this speed it would take the electrons hours to get to the lights." This completely caught me by surprise, but it makes sense once it's pointed out. Imagine a pipe filled with solid balls that just fit in it, with little friction. If you push a ball in one end, a ball pops out the other almost immediately. But not the same ball! Even if you keep pushing balls in, that first one you pushed will take a while to get the other end. Update: as rrobukef notes in a reply, this would be the case for direct current (DC). With the usual household alternating current (AC), the electrons barely move at all! https://www.uu.edu/dept/physics/scienceguys/2001Nov.cfm https://www.uu.edu/dept/physics/scienceguys/2001Nov.cfm https://wtamu.edu/~cbaird/sq/2014/02/19/what-is-the-speed-of-electricity/ https://wtamu.edu/~cbaird/sq/2014/02/19/what-is-the-speed-of...
- spurgu 6y agoActually, 0.02 cm * 60 seconds = 1.2 cm (not inches).
- rrobukef 6y agoFor AC, they move back as well. Thus electrons move less than 4µm from their original place (excluding Brownian movement, I assume)
- quickthrower2 6y agoAnother mindblower: you can chuck a capacitor at the other end and you’ve got a circuit with one wire! Hence you can get shocks from one live wire.
- WrtCdEvrydy 6y agoYeah, Physics 2 blew my mind with things like this. The electrons actually move mostly side to side as they bump into each other. Pushing power just pushes the ones further down the pipe into the light, not the ones entering the copper cable.
- aazaa 6y agoScience doesn't "prove" hypotheses - it disproves them. For this to work, a hypothesis must be falsifiable. Most pseudoscience (and religion) makes non-falsifiable claims, meaning they are incompatible with scientific discourse. This simple observation is a powerful tool in any bullshit-detection kit. Once produced, a scientific hypothesis of any merit will be attacked vigorously with experiments until enough parties are convinced that disproof is sufficiently unlikely. The process isn't always pleasant for those making the falsifiable claims. Sadly, this is not how science is taught in most schools. There, students are given the "truth" and, on a good day, asked to verify it experimentally. We are now living with the terrible consequences of generations of youth who think science is about "proving" the truth.
- christiansakai 6y agoVery interesting
- hprotagonist 6y agoIronically, of course, Popperian falsifiability is itself unfalsafiable, and therefore does not meet its own definition as a member of itself. Popper knew this, by the way. So the inverse to the trap you point out here is the claims that "if not falsifiable, then unable to be true/useful", which is just as specious.
- seanwilson 6y agoIsn't this like saying if X is an axiom and you can prove Y via X, you shouldn't trust Y is true because you can't prove X is true? What systems for determining the truth exist that aren't built on top of some fundamental axioms?
- hprotagonist 6y agonone; you have to at least claim as an axiom "axioms are things that can be claimed" -- but that's not what's under discussion here: logic and math are neither of them empirical sciences, after all. my point is that "we define science as empirical falsificationism" is itself nonscientific by its own definition, and that that's OK, still capable of being true, and is a handy way to get stuff done.
- merpnderp 6y agoThat 'normal' matter only makes up 5% of the universe. That some omnipresent dark energy field makes up the majority (63%) of the universe.
- xlm1717 6y agoThe selective attention test, aka the "invisible gorilla" experiment, and the finding that 50% of people didn't see the gorilla.
- rimunroe 6y agoFrom Introduction to Elementary Particles by David Griffiths: a neutrino of moderate energy could easily penetrate a thousand lightyears of lead.
- dmckeon 6y agoOnly 10% of the cells in a human body are human, but that 90% is only 2-3% of human body weight. https://www.nih.gov/news-events/news-releases/nih-human-microbiome-project-defines-normal-bacterial-makeup-body https://www.nih.gov/news-events/news-releases/nih-human-micr...
- sloaken 6y agoSo if your body was a democracy, you would lose.
- teh_klev 6y agoOk, so maybe not a "fact" but the hypothesis of the False Vacuum: https://en.wikipedia.org/wiki/False_vacuum https://en.wikipedia.org/wiki/False_vacuum This quote blew my mind: "The possibility that we are living in a false vacuum has never been a cheering one to contemplate. Vacuum decay is the ultimate ecological catastrophe; in the new vacuum there are new constants of nature; after vacuum decay, not only is life as we know it impossible, so is chemistry as we know it. However, one could always draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain, if not life as we know it, at least some structures capable of knowing joy. This possibility has now been eliminated." I immediately went out and bought Greg Egan's "Schild's Ladder" after find out he'd used this as a plot device.
- cercatrova 6y agoYou should also read the Three Body Problem trilogy, specifically the last book, although I won't spoil it. It uses a plot device very similar to a false vacuum.
- akmarinov 6y agoThe sun orbits the center of the galaxy every 250 million years, so when the dinosaurs were around, they were on the other side of the galaxy, compared to where we are now.
- mistersquid 6y agoIn Physics 2 (Light, Electricity, and Electromagnetism), I could not derive the correct answer for calculating the flux of an infinite sheet. TA: The flux is S for an infinite sheet. Me: How? We have S for this side plus S for the other which yields 2S! TA: For an infinite sheet, there is no other side. Me: O_O
- jabirali 6y agoTo me that sounds mostly like a philosophical distinction. In most physics calculations, “infinite” just means “finite but so large that we can neglect edge effects”.
- pyfgcrl123 6y agoThat had interactions between protons and neutrons been but a tiny bit weaker or stronger than they are, the universe would probably contain a lot less carbon, nitrogen and oxygen (https://en.wikipedia.org/wiki/Triple-alpha_process#Resonances https://en.wikipedia.org/wiki/Triple-alpha_process#Resonance...), perhaps precluding existence of life as we know it.
- mjevans 6y agoFor me it's material science misconceptions, corrections to what a kid / the over-simplified public conception are. As I'm not a material science expert, if I'm wrong or slightly incorrect please explain what actually happens. "diamonds are forever" It's appealing to believe that a crystalline structure, a pretty one too, might exist until actively changed. Diamonds are not forever. What 'blew my mind' is that diamonds are the result of compression and very slowly decompressing. That slowly over time the outer layer leaves that state and turns to dust. Glass is a 'liquid' I'm much less sure about glass, I'm not even sure that science is sure about glass. Apparently one process for making glass in the old days involved something blowing and spinning discs of it to produce nearly flat segments. When installed the artisan making the window would place the thicker end down for stability or some other reason. I'm not positive if glass is a liquid or not, but the reason many people might think it's a liquid is that intentional selection bias when fitting the panes of glass. The whole concept of glass possibly being a liquid though changed the way I perceive solid, liquid, and gas states. Those labels better reflect much more temporally localized potential change and interaction than they do to uniquely describe matter. BTW, if there is an expert, is glass actually a liquid or a solid?
- pauldelany 6y agoMay be wrong, but I think it correct to say glass is a 'fluid' (it flows - very slowly), gases and liquids are generally fluids. But glass is not a liquid.
- tashmahalic 6y agoGravity travels at the speed of light (the speed of causality). If the sun suddenly disappeared, the earth would continue orbiting around where it used to be, for about 8 minutes. Nothing can travel faster than light through space, in a vacuum. However, if you pick two points in space that are far enough apart (e.g. at opposite sides of the observable universe), these points will be moving apart faster than light, because space itself is expanding. The expansion of space isn’t coming from a single point outward, like an explosion. It’s expanding by the same amount at every point in the universe. People analogize this in lower dimensions to stretching fabric or blowing up a balloon.
- masked_titan 6y agoHow do we know that the space is expanding if there is nothing to compare it to?
- tashmahalic 6y agoThe farther away a galaxy is, the more red-shifted the light from that galaxy is, when it reaches us. Also, really far-away galaxies are receding from us faster than light. And, the existence of the cosmological event horizon seems to support this too, I think. Things beyond that horizon will emit light in our direction, but that light will never reach us. In fact, without this horizon, I believe that the night sky would be much brighter. I find it kind of sad that, as time passes, more of the universe becomes unobservable. Eventually the only stars visible from our POV will be those in our own galaxy (and galaxies that ours has merged with, in the interim). More info at https://en.wikipedia.org/wiki/Expansion_of_the_universe https://en.wikipedia.org/wiki/Expansion_of_the_universe
- cvhashim 6y agoThis question feels AskReddity
- RaoulP 6y agoIt never fails to amuse me that any pressure or force that we intuitively feel is "pulled" by a vacuum, is only caused by air pressure on the other sides of an object. When you see something hanging from a suction cup in your kitchen or bathroom, it's fun to imagine that the air around you is hammering the suction cup enough to keep it stuck there. With quite some force you'll notice, if you try to pull it straight out! But let some air in through a small gap, and it will help even things out. A lack of air by itself does nothing. It's just about the net forces.
- Corrado 6y agoWow, I never thought about that before. So, if you could draw a vacuum in your whole kitchen or bathroom, would the suction cup fall down?
- s_gourichon 6y agoYes.
- RichardCA 6y agoThat something trivial like seeing speckle patterns in my eyes when I'm tired is proof of the quantum nature of light.
- AnimalMuppet 6y agoInteresting. How does that work?
- RichardCA 6y agoI'm sure I'll do a poor job articulating it. It's similar to bokeh that photographers are familiar with. You look at a light source and the light seems to bounce through the pupil and back out again. If there's a drop of liquid on your eyelashes you'll see a bokeh ring with interference ripples around the edge. I just remember as a child I thought it was strange, then in high school physics I saw how laser light was always grainy, and even things like the solidity of matter can be thought of as optical illusion (caused by the wavelengths of visible light casting a well-defined shadow). Then later I got into photography and realized what you can do with even a little knowledge about light and optics. I still have a sense of wonder about it even though I'm an average shooter at best. Hope that all made sense.
- RichardCA 6y agoThis is what I'm taking about, when I was a kid before I got fitted with glasses, I remember the world looking like this... https://photo.stackexchange.com/questions/99407/what-is-the-cause-of-inclusions-in-my-bokeh https://photo.stackexchange.com/questions/99407/what-is-the-...
- AnimalMuppet 6y agoOK, but that's proof of the wave nature of light, not quite of the quantum nature.
- RichardCA 6y ago
- yongjik 6y agoBTW, "it takes a photon over 100,000 years to exit the Sun" is misleading - it sounds like there's a single photon that's generated deep inside the Sun's core and winds its way through like a cicada until it emerges at the surface. In reality, any photon traveling inside the Sun will almost instantly collide with some other particle, which may emit zero, one, or more photons as a result. When we say "100,000 years", I believe we're summing up the total of these photons' expected lifetimes, basically following the flux of energy rather than individual photons.
- JohnDeHope 6y agoI absolutely cannot psychologically deal with the Monty Haul paradox. https://en.wikipedia.org/wiki/Monty_Hall_problem https://en.wikipedia.org/wiki/Monty_Hall_problem I've coded it multiple times in multiple programming languages as a cathartic exercise. Despite seeing the results obviously printed out in a console in front of me, I just can't handle it. I lose SAN just thinking about it.
- spurgu 6y agoA bit late to the party (came from Hacker Newsletter) but it seems obvious to me: - If you happen to choose a door with a goat (⅔ of the time), the host has to choose a goat door, leaving "switch" a guaranteed win - If you happen choose the door with the car (⅓ of the time), the host opens a random goat door and you have 50/50 between staying and switching So always switching is the correct move - if you do that you'll win the ⅔ of the time (every time you open a goat door).
- cbruns 6y agoThe explanation that makes the most sense to me, from wiki: Yet another insight is that your chance of winning by switching doors is directly related to your chance of choosing the winning door in the first place: if you choose the correct door on your first try, then switching loses; if you choose a wrong door on your first try, then switching wins; your chance of choosing the correct door on your first try is 1/3, and the chance of choosing a wrong door is 2/3.
- JohnDeHope 6y agoThe bit that gets me... If he opens one door, which is a goat, so there is 1 goat and 1 prize remaining... then the chance should be 50% staying put or switching, right? That's the part that gets me. The whole bit about 3 doors and opening one of them and "do you want to switch" is all a ruse, it seems to me. At the end of the day there are two doors, one with a goat and one with a prize, and however you choose between 2 doors, you will win or lose 50% of the time. Right? Aargh the SAN loss...
- 6y ago
- Chris2048 6y agolook at the time-lines of the universe and some of the entries, especially the last few, are mind blowing ( https://en.wikipedia.org/wiki/Timeline_of_the_far_future https://en.wikipedia.org/wiki/Timeline_of_the_far_future ) e.g. "Due to the gradual slowing down of Earth's rotation, a day on Earth will be one hour longer than it is today" "From its present position, the Solar System completes one full orbit of the Galactic Center" "All the continents on Earth may fuse into a supercontinent (Pangaea Ultima, Novopangaea, or Amasia)" "Tidal acceleration moves the Moon far enough from Earth that total solar eclipses are no longer possible." "the Andromeda Galaxy will have collided with the Milky Way, which will thereafter merge to form a galaxy dubbed "Milkomeda" ... There is also a small chance of the Solar System being ejected. The planets of the Solar System will almost certainly not be disturbed by these events" "time until stellar close encounters detach all planets in star systems (including the Solar System) from their orbits" "time until those stars not ejected from galaxies (1–10%) fall into their galaxies' central supermassive black holes. By this point, with binary stars having fallen into each other, and planets into their stars" "estimated time for rigid objects, from free-floating rocks in space to planets, to rearrange their atoms and molecules via quantum tunneling. On this timescale, any discrete body of matter "behaves like a liquid" and becomes a smooth sphere due to diffusion and gravity" "... they [Positrons] find a distant electron to pair with and the two enter into a highly excited state of positronium, with a radius larger than the current universe. Over the next 10^141 years they will gradually spiral inwards until they finally annihilate" "time until a supermassive black hole with a mass of 20 trillion solar masses decays by Hawking radiation ... marks the end of the Black Hole Era. Beyond this time, if protons do decay, the Universe enters the Dark Era, in which all physical objects have decayed to subatomic particles" "... time for all nucleons in the observable universe to decay ..." "... estimated time until all baryonic matter in stellar-mass objects has either fused together [into iron-56] ... or decayed from a higher mass element into iron-56 to form an iron star" "Estimated time for a Boltzmann brain to appear in the vacuum via a spontaneous entropy decrease" "estimate for the time until all iron stars collapse into black holes ... which then (on these timescales) instantaneously evaporate into subatomic particles ... Beyond this point, it is almost certain that Universe will contain no more baryonic matter and will be an almost pure vacuum until it reaches its final energy state ..." "Because the total number of ways in which all the subatomic particles in the observable universe can be combined is <big number> a number which, when multiplied by <big number>, disappears into the rounding error, this is also the time required for a quantum-tunnelled and quantum fluctuation-generated Big Bang to produce a new universe identical to our own ..."
- cameronfraser 6y agocamels have three eyelids
- m463 6y agoTrees form out of thin air.
- juancn 6y agoInformation has mass (and thus energy). As in a full hard drive weighs more than an empty one. https://aip.scitation.org/doi/10.1063/1.5123794 https://aip.scitation.org/doi/10.1063/1.5123794
- Corrado 6y agoThe gold in my wedding ring was formed inside a star. I kinda sorta knew all matter was formed inside stars but it never really clicked until I thought about something as simple as a lump of gold and where those atoms really originated.
- AndrewOMartin 6y agoRelated, most of the atoms in a new born baby are 13.7bn years old.
- riffraff 6y agoas Moby would say, we are all made of stars. It was a bit mindblowing to me to realize this was true and not just some hippie-ish slogan. [0] https://en.wikipedia.org/wiki/We_Are_All_Made_of_Stars https://en.wikipedia.org/wiki/We_Are_All_Made_of_Stars
- giantg2 6y agoHot water freezes faster than cold water (sometimes).
- bjourne 6y agoExactly anything you can think of can be represented as a segment of pi's infinite decimal expansion.
- atmosx 6y agoNot a science fact per se: Until recently I haven't realised the amount of damage inflicted by religion or in the name of religion if you will, to our species. Take Heliocentrism[^1] for example, it was alluded in the 5th century BC that the Earth revolves around the sun and that stars are other "suns". Then religion came along. Galileo nearly died for re-iterating a theory that was accepted by part of the scientific community nearly 2000 years before him. In similar fashion, years ago while studying the circulatory system for the anatomy class I came across a wikipedia article. This particular part of the circulatory system was documented in detail by Egyptians in 200 BC. Knowledge came from the mummification process. The next breakthrough in this area was made in the 19th century. Looks like our species could have a colony in Mars by now, if science were allowed to breakthrough linearly. [^1]: https://en.wikipedia.org/wiki/Heliocentrism https://en.wikipedia.org/wiki/Heliocentrism
- DevX101 6y agoI'm not personally religious but I'd be very careful before assuming religion, an institution that's been with humans for thousands of years, was a net negative. I think humans probably have some innate desire for institutions with religious-like properties. And as we've become more secular over the past 60 years, there's been an increase in people that seem to be making politics the replacement, which may end up being more destructive than theistic religion ever was.
- atmosx 6y ago> I think humans probably have some innate desire for institutions with religious-like properties. Hm, but we grow in a religious setting, the larger part of the population. So, is it an innate desire or a designed reality for population control?
- bruce511 6y agoReligion is an ambiguous term, which can be why arguments of this sort can get out of hand. To some, religion = faith. And I think you'll find that most faith has little to say about science (and in the case of your example says nothing about the earth/sun relationship). More commonly though, when referencing Religion you are really talking about Politics. Heliocentrasim, the crusades, Muslim terrorism, are all about politics, not faith. When you make an argument using the word Religion in a political sense, but others read it as attacking their faith, then things get very ugly. In other words you can be a devout Christian, and still consider the crusades to be awful. And you can be a good Muslim and consider 9/11 to be an act of war. Most anytime someone talks about religion as being the cause of war and conflict, the root cause is politics, not faith.
- macando 6y agoCreating something out of nothing: The Banach - Tarski Paradox https://youtu.be/s86-Z-CbaHA https://youtu.be/s86-Z-CbaHA
- Caylio 6y agoThat's a consequence of the axiom of choice, which has historically been a highly controversial axiom.
- yuningalexliu 6y agoYou always weigh less in the morning compared to the previous night because you have exhaled carbon atoms from your body!
- buwka 6y agoIsn't most of reason you weigh less in the morning than at night due to the amount of water weight you have lost while sleeping.
- meiraleal 6y agoA man can fast for more than a year without die https://en.wikipedia.org/wiki/Angus_Barbieri%27s_fast https://en.wikipedia.org/wiki/Angus_Barbieri%27s_fast
- BrandoElFollito 6y agoI usually ask people to imagine they are putting a rope tight around the earth, following the equator (idealized sphere). Then they add 1 meter to the rope (it is now longer by a meter) and spread it around the earth uniformly (it hovers above the earth, everywhere at the same distance from the earth) Estimate that hovering distance. Try yourself to estimate it, then make the calculation.
- quickthrower2 6y agoBlack hole singularity is infinitely dense and zero size