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
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.
If you can see the moon (if it is "up" at night).
Yup
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.
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.
~~dim~~
Disappear
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…
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?
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?
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 path~~ travel 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.
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.
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.
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
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.
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.
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