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Ask HN: What is a science fact that blew your mind when you learned it?

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Re: Ask HN: What is a science fact that blew your mind when you learned it?

#31

Post by Xcelerate »

A 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.

Re: Ask HN: What is a science fact that blew your mind when you learned it?

#32

Post by perk »

cbsks wrote: post #23

I think "mind blown" is an accurate description when I first saw the Hubble Deep Field image: 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.

Don't know exactly why, but thinking about the vastness of the universe always cheers me up. Thanks for sharing :)

Re: Ask HN: What is a science fact that blew your mind when you learned it?

#35

Post by AnotherGoodName »

Xcelerate wrote: post #31

A 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 a…

>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.

Re: Ask HN: What is a science fact that blew your mind when you learned it?

#37

Post by blablabla123 »

fsflover wrote: post #22

Many statements here: https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future

> 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

I really like that theorem

Re: Ask HN: What is a science fact that blew your mind when you learned it?

#38

Post by Stratoscope »

Electrons 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://wtamu.edu/~cbaird/sq/2014/02/19/what-is-the-speed-of...

Re: Ask HN: What is a science fact that blew your mind when you learned it?

#39

Post by adsjhdashkj »

hbcondo714 wrote: post #12

Growing 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-d...

What level of drinking would cause this, though?

Re: Ask HN: What is a science fact that blew your mind when you learned it?

#40

Post by aazaa »

Science 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.

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