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.
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[ 5.1 ms ] story [ 219 ms ] threadif you close one eye and keep the other open you'll suddenly see one side of your nose.
> Can explain DNA
...
> Can see his own nose
https://en.wikipedia.org/wiki/Andromeda_Galaxy
Thousands of similar questions on reddit for anyone interested- https://duckduckgo.com/?t=ffab&q=science+fact+site%3Areddit....
(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).
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
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?
https://www.scientificamerican.com/article/the-adult-brain-d...
That's why haven't had a drink for the last 5 years
(the famous rat experiment with the "stimulating environment" and brain grown was later attributed to the exercise wheel)
[0] https://www.vice.com/en_us/article/zmjwda/a-code-glitch-may-...
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
Anyone got a link?
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!
Please note that physics as science in general is advancing constantly, but mainstream physics advances in sprints. Currently, walking droplets and Pilot Wave Theory are not good enough to be included into mainstream physics.
But it is more complicated that this. Consider https://en.wikipedia.org/wiki/Elitzur%E2%80%93Vaidman_bomb_t... -- if you only poke the particle in a "parallel universe", that also changes its pattern in this one.
At the end, quantum physics says there are multiple "versions" of how the particles move, and those versions interfere with each other. By interacting with each other, particles become entangled, which means that the "versions" of their states are no longer calculated independently, but together.
There are disagreements of what exactly this means: some people believe that reality only has multiple "versions" on a microscopic level, but when the entangled configuration becomes large enough (how large? no one knows), the parallel computation collapses, one of these "versions" is randomly selected to become the actual reality and the remaining ones disappear. Other people believe that multiple "versions" is the whole story; that observing the outcome means that you (being composed of particles that follow the laws of physics) also become entangled with the particles in the experiment, and now there are multiple "versions" of you, each observing a different outcome.
So, I'd say you got it half-right. Yes, it is about "observation = interaction"; and "observer" is just a shortcut for "the thing that poked the experimental particle, optionally also a display connected to that thing, optionally also a person observing the display". (That is, you could also have a completely impersonal "observer", e.g. a machine that measures the particle but no one is looking at its display.) But quantum physics is a different thing than mere classical physics where you correct for photons being actual things that hit the measured particle. It means there actually are multiple outcomes, which then interfere with each other, at least on the microscopic level.
In order to obtain the information you wish to 'observe', you need to interact with it.
That interaction 'collapses the wave function', or rather, you become part the wave function, but seeing it 'from the inside' looks different compared to from the outside.
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.
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!)
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.
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.
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.
https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future
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
I really like that theorem
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!
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.
https://www.wthr.com/article/news/investigations/13-investig...
Wow... just... mind blown. I always read about it, but never experienced it... wow...
So my trip to the grocery store could be adding as much carbon dioxide to the air as the groceries I pick up!
I use that as a way to visualize the problem with "a solution".
Maybe dental implements.
At least that's my pedestrian interpretation :)
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.
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.
This is false. The dilemma is that you can't "just weigh" a compressed spring without assistance. However, you can get around it by weighing a compression device with the spring, both when it's compressing and not compressing the spring. The weight will be the same.
Weight is mass times gravity. It is the mass of the object. As affected by a single force - gravity. Gravity is a force.
A spinning ball has ANOTHER force acting on it, and therefore cannot be defined by "weight".
In short, this is an absurd statement that tries to redefine a scientific definition for...I don't even know? Sensationalism?
All forms of energy, including potential energy in the form of a compressed/stretched spring, couple to the gravitational field. Again, read about the stress-energy tensor for how this works.
> In short, this is an absurd statement that tries to redefine a scientific definition for...I don't even know? Sensationalism?
What I've said is not even remotely controversial in the physics community. Don't take my word for it; ask anyone who has taken a basic graduate course in general physics and they will agree that a compressed spring or a spinning ball weighs an imperceptibly (i.e., immeasurably) small amount more than the uncompressed spring or stationary ball, should you have a hypothetical scale that was so precise as to be able to measure the difference.
Note however that the quoted effect – difference in weight between a compressed and uncompressed spring – will realistically be so small that I doubt you could measure that in a lab. To get a sense of how small that effect is, try comparing the E=mc^2 mass-energy of a spring to its E=kx^2 compression energy...
I thought the existence of particles was relative to how fast you're accelerating? If it's relative to how fast you're moving, wouldn't that imply that absolute velocity exists, i.e. that given two objects with known relative velocity to each other, we could potentially establish which one was "really" moving and which one was "really" still?
Can you provide a link that talks about that? It goes against my understanding of why there's an uncertainty principle at all
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://wtamu.edu/~cbaird/sq/2014/02/19/what-is-the-speed-of...
Hence you can get shocks from one live wire.
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.
https://www.allaboutcircuits.com/textbook/semiconductors/chp...