Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

news.ycombinator.com

Post reply on HN
Print view View original

81–90 of 189 posts

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

#81

Post by masked_titan »

tashmahalic wrote: post #78

Gravity 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, be…

How do we know that the space is expanding if there is nothing to compare it to?

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

#82

Post by edanm »

akmarinov wrote: post #68
ffpip wrote: post #6

Not 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....

Also chances are that no one has shuffled a deck in the same order as someone else has, ever in history.

This 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).

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

#84

Post by b0sk »

Stratoscope wrote: post #38

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.…

A ripple in a pool simply displaces the ball up and down vertically. The ball doesn't move along the wave

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

#85

Post by RaoulP »

It 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.

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

#86

Post by throw1234651234 »

Xcelerate wrote: post #57
throw1234651234 wrote: post #44

Earlier quoted context omitted.

>A compressed spring weighs more than the same spring uncompressed. 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.

You could not practically ever measure the difference in a lab, but it’s still a real effect. Look up the stress-energy tensor. I could equivalently say that a spinning ball weighs more than the same ball when stationary.

W=mg

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?

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

#87

Post by tashmahalic »

masked_titan wrote: post #81
tashmahalic wrote: post #78

Gravity 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, be…

How do we know that the space is expanding if there is nothing to compare it to?

The 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

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

#89

Post by Xcelerate »

throw1234651234 wrote: post #86
Xcelerate wrote: post #57

Earlier quoted context omitted.

You could not practically ever measure the difference in a lab, but it’s still a real effect. Look up the stress-energy tensor. I could equivalently say that a spinning ball weighs more than the same ball when stationary.

W=mg 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?

You are not considering the effect of general relativity. See theoretical physicist Professor Matt Strassler's page where he gives the exact same example of how energy can be stored that I did: https://profmattstrassler.com/articles-and-posts/particle-ph....

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.

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

#90

Post by berbec »

adsjhdashkj wrote: post #39
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?

Come over to my house and I'll show you...

That's why haven't had a drink for the last 5 years

Post reply on HN