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/sci/ - Science & Math

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1600699 No.1600699 [Reply] [Original]

I was just thinking: if the sun were to disappear, we wouldn't have any idea for 8 minutes. that's fucking insane

>> No.1600719

more like you just watched sunshine


lol.

>> No.1600724

if the sun disappeared the gravity of the earth would be fucked up and we'd all be dead before 8 minutes were over

>> No.1600731

>>1600724
So the effects of gravity are instant? as in faster than the speed of light?

>> No.1600733

>>1600724

Except it would take just as long for gravity to stop affecting Earth.

>> No.1600730

If you can just magically poof out the sun I'm pretty sure a few more photons wouldn't be too much of a hassle

>> No.1600743

>>1600724
gravity waves travel at C, just like light.

>> No.1600763

>>1600743

> Gravity waves

>> No.1600771

>>1600731
Already been tested, gravity has a delay approximately the same as the speed of light.

>> No.1600774

>>1600771

> Exactly.

>> No.1600775

>>1600743

nope, gravity affects spacetime and relativity, giving off instantaneous effects

>> No.1600778

>>1600775

> Not sure if trolling.

>> No.1600783

http://en.wikipedia.org/wiki/Speed_of_gravity#Possible_experimental_measurements

>Kopeikin and Fomalont concluded that the speed of gravity is between 0.8 and 1.2 times the speed of light, which would be fully consistent with the theoretical prediction of general relativity that the speed of gravity is exactly the same as the speed of light.

herp de derp

>> No.1600787

>>1600699
I've about this since I've been a child. Fucking creepy.

>> No.1600805

>>1600775

If trolling, 6/10. If not, idiot.

>> No.1600854

>>1600743
I'm so glad all your fucking comments are saved.

Comes to show how fucking stupid you are.

>> No.1600898

>>1600724
what will we die from?

>> No.1600908

Ok, here's a question, /sci/:

Assuming that the effects of gravity travel at the same speed as light, and that the sun "magically poofed out of existence".. when those ~8 minutes were up, would the Earth IMMEDIATELY start heading off in a straight(-ish) line (warping of space disappears instantaneously), or would we continue curving slightly for a little while (space "smooths" itself out after the gravity well is removed).

>> No.1601213

>>1600908
>>1600908

http://www.youtube.com/watch?v=O-p8yZYxNGc
they say it's the latter

>> No.1601225

Gravitons are constantly exchanged between sun and earth. Were the sun to disappear, we would not have to wait eight minutes. The gravitons halfway between the two bodies would be affected by the change after only four minutes, (half the distance means half the time) which is also the same time it would take them to reach earth.

So the earth would start to leave orbit after 4 minutes.

>> No.1601228

Holy shit, i thought this board was a place for people who know about science. This whole thread says otherwise.

>> No.1601232

>>1601225

Implying gravitons exist?

>> No.1601233

>>1600908

We would continue along our current trajectory. When we revolve around something, at each instant in time we are travelling in a straight line. If the sun disappeared we would continue to travel in the straight line we were travelling in at that instant in time. Of course, that is after the 8 minutes it would take for the curve in spacetime to 'flatten' here.

>> No.1601236

>>1600783
If you keep reading there, there's obviously some controversy over the legitimacy of the experiments. Keep in mind there are two entities here: the speed of gravity propagation, and the speed of gravity wave propagation. Those I've seen argue for faster than c gravity propagation (in peer reviewed journals) generally agree that gravity WAVES travel at c. General Relativity predicts both travel at c.

>> No.1601239

>>1601228
>i thought this board was a place for people who know about science.
whoreslaughing.jpg

>> No.1601279

>>1600908
Sun explodes in a spherically symmetric manner, with the matter traveling outward at c: After 8 minutes, the earth flies off in a straight line.

Sun disappears: IMPOSSIBRU

>> No.1601282

>>1601228
>This whole board says otherwise.
fixed

>> No.1601286

>>1601228
>i thought this board was a place for people who know about science

Are you forgetting you're on 4chan?

>> No.1601351

>>1601225
>Oh yeah, gravitons. Sure.

>> No.1601372

Unless gravity propagates faster then c, then yes it would take ~8 minutes.

>> No.1601375

>>1601372
Gravity is not a force propagating but the curvature of spacetime itself, thus making the sun disappear would have instantaneous effects.

Don't listen to the trolls claiming "gravitons" exist. Just wishful thinking.

>> No.1601391

>>1601279
Also: Sun explodes in a spherically symmetric manner, with the matter traveling outward at v: After (1 AU)/v, the earth flies off in a straight line.

See Birkhoff's theorem.

>> No.1601406

>>1601375
The sun's effects on spacetime curvature have to propagate, too.

>> No.1601450

BTW Einstein's field equations imply conservation of energy. It is therefore impossible to solve for what would happen if the sun just disappeared; the equations you use to predict what will happen say the sun will not disappear.

But if some energy-conserving process, like an explosion, destroyed the sun, whatever the gravitational effects on the earth would be, they would not be felt for at least 8 minutes.

>> No.1601469

8 minutes 12 seconds.

>> No.1601487

>Gravity is not a force propagating but the curvature of spacetime itself, thus making the sun disappear would have instantaneous effects.

Instantaneous in whose reference frame? Did everyone in this thread just forget about the relativity of simultaneity?

If gravity changes propagated faster than light, then it could be useful for superluminal communication, which could be used to violate causality with the right arrangement of reference frames.

Is this /sci/ or /fringesci/?

>> No.1601495

WHO CARES HOW LONG IT WOULD TAKE GRAVITY TO STOP AFFECTING US?

WHY THE FUCK WOULD WE DIE FROM "FUCKED UP" GRAVITY?

>> No.1601531

>>1601495
This. OP's point was about us knowing whether the sun was there or not. Anyone without access to some sort of gravity detection machine (ie almost everyone) wouldn't know for 8 minutes

>> No.1601533

>>1601487
>Implying causality is more than an often but not always useful conceptual framework

>> No.1601536

>>1601450
Let's just say somehow it teleported a million billion trillion miles away

>> No.1601540

Gravity waves propagate at the speed of light.

>> No.1601557
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1601557

Hey, my captcha's
Bhaskara's proof
I thought you'd get a kick out of that

>> No.1601584

>>1601536
If the sun was "gone" not exploded, then yes after about 8 min we'd see visual evidence for it just going away. The argument raging here is how long would we notice the gravity.

The view of Gravity under Newton is differnt then the view of Gravity post Einstein.

I personaly belive (key word belive) we'd notice the sun "dissapeared" Gravity wise (and not visual light evidecne) between relitively 10sec to 4 min after the event happend.

However thats not to say our course would radicly change for afew days since the Earth is a massive object its self

>> No.1602693

>>1600854
If you were a tripfag, I'm guessing you'd have a reputation around aether's.

>> No.1602713

>>1600787
If you think that's creepy, imagine the moon suddenly halting. Then use some simple Newtonian physics to see what happens next, and what we would see as it happened.

>> No.1602775

>>1601584
>However thats not to say our course would radicly change for afew days since the Earth is a massive object its self

With the sun there, the course of the earth is constantly changing (by almost 1 degree per day on average), as the Sun's gravity pulls us into an elliptical orbit.

The instant the effect of the Sun's gravity is gone, Earth will fly in a perfectly straight line (apart from the small course deviations caused the the other planets).

I don't think anyone would notice the change in course though, except for people operating telescopes who will see the stars in slightly different positions than they are expecting.

>> No.1602785

>>1602713

It would fall toward the earth, wouldn't it?

>> No.1602801

>>1601536
That's also inconsistent with Einstein's field equations. They imply local conservation of energy, not global.

>> No.1602849

people seem to know a lot about one of the least understood forces....

>> No.1602858

>>1602849
Yes, we do know a lot about it. Not knowing the ultimate quantum theory doesn't stop us from knowing quite a lot about its behavior at macroscopic scales.