If I understand that right, gravity also moves in space at the speed of light, therefore Earth will keep on orbiting for 8min around nothing?
Kind of. The concept of simultaneity breaks down at distances where the speed of light matters. If we base it on what we currently observe and call “now” on the Sun the eight minute old state we currently observe then what does “now” on earth look like from the point of view of the Sun at that same moment? You can’t reconcile a single “now” for observers in both locations.
An alternative take which is also consistent with observable physics is that the speed of light is infinite but it’s causality itself that propagates at c.
Thinking in those terms also makes a number of relativistic effects more intuitive. You need infinite energy to reach the speed of light simply because it’s infinitely fast. Time dilates when moving because you’re encountering approaching causality earlier than you otherwise would have. Time “stops” for anything traveling at the speed of light because at infinite speed it just experiences literally everything in its line of travel at once and the concept of “after” becomes meaningless, encountering all future oncoming causality in a single instant.
This was a bit of a tangent but it’s something that has fascinated me for a long time.
I’m trying to understand how that reference frame works when you just just bounce a photon off a mirror and time how long it takes to come back? Like, light must have a non-infinite speed to the stationary observer, or it wouldn’t take time to traverse the distance.
thats the thing, thats from your reference frame. From the photons perspective time stands still and everything happens at once
Well, yes. Sorry, I thought the claim was that photons move at infinite speed, relative to a stationary observer.
But that also doesn’t translate. If the moment the photon is created (from whatever reaction that caused the light source), to the moment it hit the person’s eyes had no time pass (nothing in the universe moved) then it would be instantly created and observed by the observer. But the moment the switch turns on and the moment the photon hits the observer (as miniscule as this distance is) the eye of the observer has moved from A: switch goes on to B: observed.
Yeah no time passes for the photon I guess, but the universe still moved around the photons travel.
Let’s preface this, I’m no astrophysicist. but from my understanding:
That’s just the thing, different speed observers do not agree on when things happen, or even the shape of the universe. The faster you go the more the universe compresses in front of you, making distances shorter from your frame of reference.
From the photons perspective it instantly moves through an infinitesimally thin sheet of universe. Everything that “happens around it” from our frame of reference all instantly happens at once if you ask the photon.
Here’s a really good explanation from someone far smarter than me https://youtu.be/-NN_m2yKAAk
The observable effect is the same either way. If light is infinitely fast and causality propagates at c then it’s still going to take (distance to the mirror / c) for the fact that you turned on the light to reach the mirror, and that same amount of time for the fact that the light reflected to propagate back to you.
Those two things don’t square. If you’re moving relative to the mirror when your fire the photon, it would hit in a different place than if you were stationary. The photon can’t be moving infinitely fast in your reference frame for that to happen.
Yeah I think infinite is the wrong word for them to use there. Maybe call it maximally fast? Like it goes as fast as possible no matter your reference frame, but that speed is limited by the speed of causality. The photon has 100% of its skill points in speed through space and 0% on speed through time.
Would it? What does “stationary” mean when discussing relative velocities? The mirror being stationary and the person firing the photon moving at a constant velocity is literally an indistinguishable scenario from a stationary person firing the photon at a moving mirror.
If I am moving relative to a mirror when I fire the photon, then the mirror is moving relative to me, and will be in a different relative position by the time the “event” of my firing that photon reaches it.
Also, the photon isn’t moving infinitely fast in my (the firer’s) reference frame. It’s moving infinitely fast in it’s own reference frame.
Yeah I eventually picked up that that’s what you meant in your original comment, not that photons move instantaneously and that causality somehow catches up later.
Information can only travel at the speed of light.
Yes, but bad news travels much faster, and the sun disappearing would be very bad news to at least some people.
bad gas travels fast in a small town
It’s sort of how if you hold a slinky on one end hanging down, then drop the slinky, bottom will not start falling until the top reaches it. In a sense, bottom will be hanging onto nothing. But of course that nothing is tension from the top of the slinky.
That was an intuitive way to think about it, thank you.
That is correct as weird as it sounds
The sun could be gone but its influence would remain. Kinda like getting out of a pool and looking back to see the waves on the surface that you caused.
Wouldn’t you see the effect on the moon?
Only if the moon is up.
Moon is a fake bitch.
Imagine seeing the moon just switch off
That would be a beautiful, terrifying sight. You could gaze up at the most amazing view of the stars as the whole world froze to death.
I wonder if you had the opportunity to do so leisurely.
A suddenly vanishing sun would also mean a spectularly high energy gravity wave hitting the earth. You might be dead before even realizing that anything is off…
Would that wave be that destructive? I can definitely see it screwing up the orbits of Jupiter’s moons, maybe even our own moon, but would it be much worse than a small earthquake?
The Sun’s gravity at Earth’s distance is only 0.0059m/s². I’m not exactly certain about how the magnetude of a gravity wave relates to the magnetude of the static force, but even if the force fluctuates rapidly at ten times the static force, that’s less than a hundredth of a g; enough to be perceivable but you wouldn’t even loose your balance.
I wonder if the sudden change in direction would be the bigger problem, as we no longer had the sun to orbit around.
This is a good question for Randall Monroe, if he hasn’t already addressed it.
I thought the same after writing the gravity wave comment. Really not sure what the effects would be and the equations involved are far from intuitive…
Is Randall doing new What-If stuff? I have only seen old articles on his website recently.
There is a really great short story by Larry Niven based on a similar premise:
“Inconstant Moon”
There is also an “Outer Limits” episode based on this. I watched that before knowing the short story and it is one of only 2 or three OL episodes that I still have an active memory of…
Yup
If you can see the moon (if it is “up” at night).
There’s a pretty cool short story where a guy is looking at the full moon and he realizes that it’s gotten way too bright, and that could only happen because the sun has just spontaneously exploded, and he basically just makes peace with the fact that the world is going to be destroyed very shortly.
Assuming its midday, and the moon is on or near the horizon, it would actually still be seen for an additional 1.3 seconds after we see the sun disappear. If its high in the sky however, it would disappear only a few ms after the sun, unless it was in a full or partial eclipse, where it would disappear at the same time to our eyes.
Yeah - half a second before seeing it on the sun.
It goes to 9 minutes from 8, since every single communication gadget will yell out that the sun has disappeared as reports come in from the other side of the earth.
Depending on the lunar cycle, the night time side would notice the moon become dim.
dimDisappear
Ok yeah you’d definitely want any story to have the sun disappear take place at night, with a full moon, possibly a large harvest moon for ambiance. The moon disappears and within minutes you’re bombarded with calls…
Well technically there’d be earth glow so it wouldn’t be totally dark.
Earthshine from where? That’s still reflected sunlight! Maybe a tiny amount of cityshine, but the light pollution from those same cities will far outshine that.
Like you said, artificial lighting. Technically you’d get some IR from the planet itself which could get converted to visible light but definitely not nearly enough to be noticeable. You’d also probably get about 3 seconds of real reflected sunlight before that also goes away.
Doubt anyone would notice the moon getting dim when the fucking sun disappears in the same second.
That is actually correct. The difference of being on the opposite side that faces the sun is just a few thousandths of a second, but it is there.
Now I am curious, somebody explain. if it just stopped burning, would we know after 8 mins, if we lived on the opposite side?
Moon would “disappear” when it no longer reflected Sun’s light.
It would also start getting very cold fast
It would probably take more than a day for the cold to be so intense that you can’t possibly explain with some normal local phenomenon.
The moon might be on the daylight side, so we wouldn’t necessarily observe that.
Any visible planet or asteroid would. So some stars would also appear to blink out, but those would take longer to blink out. So the moon would go after 8 minutes, Jupiter would take 43 minutes to stop receiving light, and another 35-52 minutes to disappear for earth depending on orbital locations.
Presumably we would get something on radio/tv/internet from the side facing the sun once they realized it, that of course being only if they hadn’t already been eradicated by a horrific shockwave caused by whatever event caused the sun to vanish before they had a chance to report what they saw, because supernovae tend to travel at very close to the speed of light, so there wouldn’t be much time for them to react.
And if this is a supernova, you might just have time to grok what happened before the planet was obliterated under your feet from the shockwave.
So I guess… chances are we would just barely understand what happened before we were gone.
It’s kind of odd that it doesn’t matter for a single human whether they die from sudden car accident or get obliterated by supernova. Both events feel equal
Does heat travel at the speed of light? I just realized I have no idea how the heat from the sun travels to earth.
The “heat” IS the radiation. So, yes.
Someone correct me if I’m missing some nuance here, but heat doesn’t get transferred directly through space because heat is vibrating molecules and space is a vacuum. The sun radiates (speed O’ light). A lot of that radiation just reflects off the earth (or we wouldn’t be able to see it), but a lot of it gets absorbed. THAT’s when it’s converted into heat energy. It’s also why the greenhouse effect is a global phenomena: light energy comes in across the vacuum relatively easily, turns to heat on Earth instead of being reflected, heat energy cannot escape as easily as light energy.
Infrared light is absorbed quite easily, producing heat, and the sun emits a lot of it. Of course, all photons that are absorbed and not reflected will produce thermal energy, and infrared radiation is commonly referred to as radiant heat. The other two heat transfer methods are conduction and convection, which requires a medium to transfer through.
Neat! Thanks for sharing.
When there is a total solar eclipse, the temperature does drop dramatically. But it might not be detectable on the other side right away for sure.
It does! And if you’re in a place where night animals are noisy, they get noisy for the length of “dusk”, totality, and “dawn”!
Yes, we have conduction, convection, and radiative heat transfer. Vacuum insulates the first two, it’s the light from the sun that heats us up
I wonder how cold how fast.
It wouldn’t really be faster than normal nighttime cooling. However, that cooling would continue instead of having the sun to start warming stuff up in the morning.
It takes 8 minutes for the light to travel from the sun to Earth. Because light in a vacuum travels faster than anything, including information, we would not and could not know it had disappeared for 8 minutes. This means Earth would continue to follow its orbit around a non-existent sun for 8 minutes because the Sun’s gravity would still be acting on the Earth.
If it was nighttime, you wouldn’t notice the sudden lack of sunlight (other than if it was a full moon) but you’d almost certainly notice the change in gravity.
Edit: actually, you wouldn’t feel any difference in gravity or experience any change of acceleration. What you would experience is a very tiny vibration, of 1 million push notifications being sent to your phone from the other side of the planet.
Interesting, so you are saying light is faster than gravity?
Equal to speed of light in vacuum
light speed = gravity speed
From an AI, so take with some salt:
Yes, gravity is believed to travel at the speed of light.
According to Einstein’s theory of general relativity, the effects of gravity propagate through spacetime at the speed of light. This means that if a massive object were to suddenly change its position, the gravitational effects would not be felt instantaneously by objects around it, but would instead spread outward at the speed of light.
This is in contrast to the classical Newtonian view of gravity, which treated it as an instantaneous force. Einstein’s theory showed that gravity, like other forms of electromagnetic radiation, obeys the speed limit set by the speed of light.
Experimental evidence, such as observations of binary pulsars, has confirmed that gravity does indeed propagate at the speed of light, as predicted by general relativity. This is a crucial aspect of our modern understanding of the nature of gravity and its relationship to the fabric of spacetime.
I don’t think you’d actually “notice” the gravity.
Earth would still retain it’s mass, and we’re much closer to it, so it’s lesser mass acts much more on us than the sun’s greater.
Though, the earth would stop orbiting the sun and
travel on a mostly tangential pathtravel nearly radially away from where the sun was, instead of the elliptical path it currently travels.This is a very interesting physics question that I may look into further. Specifically what would the theoretical acceleration be, due to the lack of the sun? Is it above a humans level of perception?
Gravitysimulator.org has an interface you can simulate what happens, though it’s timeframe is on the order of days. Not seconds.
Why would it travel radially away? The resulting gravity wave from a disappearing stun much push the Earth a little, but changing its orbit that drastically would mostly destroy Earth anyway.
you’d almost certainly notice the change in gravity.
Really? can you actually percieve the sun gravity? Do you mean that we would get like a tsunami beause of the tidal effect? Now I kinda want a documentary about this.
It’s weird to say that light travels faster than information, because light is information. In other words, top speed for information IS speed of light.
I think that’s just the wording. My interpretation of that is any satellite or space probe sending back readings to Earth wouldn’t be faster than the sun visually disappearing from the sky. Even with the information being transmitted at the speed of light, there’s always going to be some sort of processing delay, along with the limited bandwidth of the transmission.
Yes, because of the medium of communication you are using right now.
The moon would disappear though, so you’d notice by looking at the sky if it wasn’t obstructed by clouds.
Only if the moon is on your side of the planet at the time and not already eclipsed by earth’s shadow.
We are however very connected. That shit would be global news immediately.
But we do have Twitter now.
Not anymore…
Or they will postulate its the left who put up a fake screen on the sky
I’m more interested in how long before we freeze to death.
How long will the earth’s atmosphere hold onto its heat?
I’m more interested in how long before we freeze to death.
Kurzegesagt did a great video on this thought experiment: https://www.youtube.com/watch?v=gLZJlf5rHVs&t=1
The classic sci-fi short story A Pail of Air touches on this.
If the sun disappears when? According to GR’s conception of simultaneous events, it disappears immediately.
Which two event are you talking about being simultaneous? The Sun going out and Earthers observing it? Those things will not be simultaneous in any reference frame, because they are “light-like” separated. (ie they lie on a 45 degree line in a Minkowski plot.)
I think what he means is when the light from the sun disappearing arrives at earth, that’s effectively when the event of the sun disappearing happened from the earth’s perspective.
wait, who’s he?
Yep. Imagine you’re off in space such that you, the sun, and the earth make an equilateral triangle. The sun disappears, then after 8 minutes you see it disappear. Then after ANOTHER 8 minutes you see the earth go dark, because that light had to cover two of the 8-light-minute long legs of the triangle.
Technically true since the daytime side will know first.
Well they’re not entirely wrong… I mean I turn off my notifications when I go to sleep.
unless you’re sleeping - 8 minutes and maybe 30 seconds to start seeing posts online, 10 minutes to start getting news about it
I don’t know about you, but if I start seeing headlines about the Sun vanishing, I’m assuming it’s a hoax and going back to bed.
Maybe if ony one or two places are reporting on it. If all the major ‘reputable’ news sources are reporting it; there’s a pretty good chance there’s something to it.
Yeah, but I’m not vetting the sources on that at 1am.
dw other people will, and the sun vanishing would cause mass panic and with it all laws & morality would go to go to hell. So unless you live off the grid you’re not going to get any sleep that eternal night :)
from then you’d probably have a few days to say goodbye to your friends and family, the Earth would rapidly start cooling and humanity would be lucky to have 0.0001% of people survive the first year
Iceland would have the highest chance. You have to find places that have geothermal or nuclear power and access to pod farming equipment.
So unless you live off the grid you’re not going to get any sleep that eternal night :)
You underestimate my ability to turn off notifications on my phone.
yea realistically nuclear power would be one of the few things to keep humanity going in that doomed world. There’s definitely a couple of bunkers set up to sustain life no matter the situation outside, but aside from the rich and a couple top scientists to think for them everyone else on the planet will die, honestly best course of action would be just commiting suicide with all your loved ones whilst there’s still some wood to burn for warmth.
I don’t mean the notifications on your phone I mean the screaming, shouting, and arson outside 😭
I suspect the first hour (though that might be generous) would be grave silent, then all hell would break loose. Nobody will have anything to lose
I don’t mean the notifications on your phone I mean the screaming, shouting, and arson outside
I don’t live that close to people. There’s an in between zone between being an urbanite and being offgrid.
Also, I don’t believe that people would turn blood thirsty within hours. That’s hollywood drivel and hollywood is run by sociopaths.
then wait until the 10min mark then! Would be rather odd if all news sources in unison decided to pull a prank like that
All we can see is 8 minutes into the sun’s past.
What if I have a flashlight and am underground?
In about 8 minutes and 20 seconds, we would lose the Sun’s gravitational force. Namely, gravitational waves travel at the speed of light (186,000 miles per second or 299,000 kilometers per second). This also means that we would be in complete darkness 8 minutes after the Sun disappears
https://curiousmatrix.com/what-would-happen-if-the-sun-disappeared/
What I wanna know is if gravitational waves travel at the speed of light all the time or are they influenced by media like light.
I’m 0% an expert in this, but I think they move at light speed all the time. Light is “affected” by mass only indirectly, since the light travels in a straight line through local space but space itself is curved by the mass.
Light gets caught up in mediums because those mediums have electric fields (the electrons for matter, or light itself when interfering). Thus, gravity waves will be slowed by gravity fields, like planets, stars, and galaxies.
What waves interact with also depends on the wavelength, like how radio waves can bounce off Earth’s ionosphere, but can ignore the atoms in the walls of your house. There are plenty of very large gravity waves from merging black holes and neutron stars, and those pass right through Earth. Smaller gravity waves (like from a collapsing or disappearing star) could interact with other stars, possibly reflecting off of star clusters, or even refracting through like glass if the distances were regular and the waves just the right length.
Those waves would also be delayed, just like light in glass, air, or water. Interestingly, even light still moves through these mediums at light-speed, but all it’s energy moves slower. If you had a sensitive enough detector you could see heavily attenuated light that didn’t slow down.
