B If the Sun disappeared, would the Earth continue to orbit?

[Ka Driver]

If the sun suddenly disappeared, we wouldn't know it for about eight minutes because that's how long it would take the light to travel the distance between the sun and the earth.

But I've often wondered; if the sun suddenly disappeared, would the Earth continue in its orbital path around the sun for eight minutes, or would it immediately fly off into outer space, off its orbital path around the sun, the instant that the sun disappeared?

Does gravity travel at the speed of light? I guess we won't know the answer to this question until we figure out what gravity is.

kadriver

 

[CWatters]

https://medium.com/starts-with-a-bang/what-is-the-speed-of-gravity-8ada2eb08430#.ca4xsmo1t

We were able to do a more direct measurement in 2002, when a chance coincidence lined up the Earth, Jupiter, and a very strong radio quasar (QSO J0842+1835) all along the same line-of-sight! As Jupiter moved between Earth and the quasar, the gravitational bending of Jupiter allowed us to measure the speed of gravity, ruling out an infinite speed and determining that the speed of gravity was between 2.55 × 10^8 and 3.81 × 10^8 meters-per-second, completely consistent with Einstein’s predictions.

 

[Cutter Ketch]

If the sun suddenly disappeared, we wouldn't know it for about eight minutes because that's how long it would take the light to travel the distance between the sun and the earth.

But I've often wondered; if the sun suddenly disappeared, would the Earth continue in its orbital path around the sun for eight minutes, or would it immediately fly off into outer space, off its orbital path around the sun, the instant that the sun disappeared?

Does gravity travel at the speed of light? I guess we won't know the answer to this question until we figure out what gravity is.

kadriver

Yes, the speed of light, and neither gravity nor light would tell you the sun disappeared until 8 minutes had passed. I doubt you would know after 8 minutes either. Whatever monumental cataclysm annihilated the Sun probably won't be too healthy for the Earth.

 

[CWatters]

I think it might be quite a slow death.

 

[Cutter Ketch]

I think it might be quite a slow death.

Oh! I guess "whatever cataclysm" didn't consider ALL the possibilities!

 

[Ka Driver]

That is a fantastic article. Thank you

 

[K. Doc Holiday]

https://medium.com/starts-with-a-bang/what-is-the-speed-of-gravity-8ada2eb08430#.ca4xsmo1t

I used to be good at math but I have a brain injury now.
Am I calculating correctly? The speed of gravity is faster than the speed of light? Nearly 4 billion meters per second?
Little help please
Doc

 

[jbriggs444]

I used to be good at math but I have a brain injury now.
Am I calculating correctly? The speed of gravity is faster than the speed of light? Nearly 4 billion meters per second?

What are you calculating? That is, what formula are you using with what inputs and what result?

The only quote I see that seems vaguely relevant from the referenced website is just an upper bound:

"
determining that the speed of gravity was between 2.55 × 10^8 and 3.81 × 10^8 meters-per-second, completely consistent with Einstein’s predictions
"

 

[dkotschessaa]

I used to be good at math but I have a brain injury now.
Am I calculating correctly? The speed of gravity is faster than the speed of light? Nearly 4 billion meters per second?
Little help please
Doc

No, the article says that tests confirm it to be close to $c$. 2.993 × 10^8 m/s (the lower bound given) is 290,000,000 m/s.

 

[Vanadium 50]

Am I calculating correctly? The speed of gravity is faster than the speed of light? Nearly 4 billion meters per second?

Where does it say that?

Doc

If you're going to sign your messages "Doc", might I ask what your doctorate is in?

 

[berkeman]

There has been a pretty massive Mentor cleanup in this thread. Please try to keep responses on-topic and mainstream.

 

[rootone]

... would it immediately fly off into outer space, off its orbital path around the sun, the instant that the sun disappeared?

That would require instantaneous transmission of information, something which never has been observed, and is incompatible with relativity.

 

[PhizWiz]

The Earth would not necessarily cease to orbit. To disappear does not mean that the sun no longer exists, it simply mean that it cannot be seen.

 

[Rx7man]

I can't guess on what would happen in the first 8 minutes.. but if the sun just magically disappeared (became mass-less), Yes, the Earth would fly off into outer space.. and probably assume some other orbit at some point in time

 

[dkotschessaa]

and probably assume some other orbit at some point in time

Actually now, that's the interesting part. What is the probability of it finding something else to orbit? I would say pretty low (near zero) in general, just by virtue of scale. Can we orbit one of our nearby gas giants? Where would we need to be in our orbit to get picked up by Proxima Centauri A or B?

The probabilities would be fun to calculate. And by "fun" I mean probably horrible.

-Dave K

 

[Rx7man]

Actually now, that's the interesting part. What is the probability of it finding something else to orbit? I would say pretty low (near zero) in general, just by virtue of scale. Can we orbit one of our nearby gas giants? Where would we need to be in our orbit to get picked up by Proxima Centauri A or B?

The probabilities would be fun to calculate. And by "fun" I mean probably horrible.

-Dave K

There also is a whole lot of stuff out there.. I mean Haley's comet takes 77 years to orbit and leaves our solar sytem...

 

[jbriggs444]

One has the [local] principle of conservation of energy to deal with. The sun cannot simply go away. It could, however, split into two pieces that fly away in opposite directions without violating any conservation laws. The gravitational effects of such an event would propagate at the speed of light.

The Earth is already in orbit within the Milky Way galaxy. Sending the sun away would not change that.

 

[dkotschessaa]

There also is a whole lot of stuff out there.. I mean Haley's comet takes 77 years to orbit and leaves our solar sytem...

I guess it depends on how far "out there" you are thinking. I am thinking on a universal scale there is a whole lot of nothing, but locally I suppose there is plenty of stuff for Earth to come into contact with. But orbit?

-Dave K

 

[Rx7man]

I guess it depends on how far "out there" you are thinking. I am thinking on a universal scale there is a whole lot of nothing, but locally I suppose there is plenty of stuff for Earth to come into contact with. But orbit?

-Dave K

When you see the Hubble pictures, and see that "haze" which consists of large celestial objects you can't even see, and the sky is FULL of that.. and you give yourself enough time to get out there (millions/billions of years?) I think it's likely the Earth would end up in orbit somewhere.. perhaps an orbit with a 50 million year period? Perhaps it would collide with something rather than orbit? I can't say!

 

[Rx7man]

One has the [local] principle of conservation of energy to deal with. The sun cannot simply go away. It could, however, split into two pieces that fly away in opposite directions without violating any conservation laws. The gravitational effects of such an event would propagate at the speed of light.

The Earth is already in orbit within the Milky Way galaxy. Sending the sun away would not change that.

The question to me sounded like a theoretical situation where no laws apply.. the sun just ceases to exist instantaneously with no other effects

 

[jbriggs444]

The question to me sounded like a theoretical situation where no laws apply.. the sun just ceases to exist instantaneously with no other effects

Yes, I get that. It was somewhat surprising that no other pedant had visited the thread to point out that using the laws of physics to predict what would happen if the laws of physics were violated is not really valid. So I became that pedant.

 

[dkotschessaa]

Yes, I get that. It was somewhat surprising that no other pedant had visited the thread to point out that using the laws of physics to predict what would happen if the laws of physics were violated is not really valid. So I became that pedant.

Is it really any more idealized than a problem you would find in a standard physics textbook?

 

[lychette]

Where does it say that?
If you're going to sign your messages "Doc", might I ask what your doctorate is in?

Do you realize that the title "doc" has no official educational meaning...anyone can take the title 'doc'
Doc Martens

 

[UsableThought]

I can't guess on what would happen in the first 8 minutes.. but if the sun just magically disappeared (became mass-less), Yes, the Earth would fly off into outer space.. and probably assume some other orbit at some point in time

Actually now, that's the interesting part. What is the probability of it finding something else to orbit?

I don't know if it's verboten to mention science fiction in a "General Physics" thread - and if yes then I will understand if this comment imitates the hypothetical sun & disappears. But anyway, something very much like this hypothetical situation was the originating premise of the 1933 pulp sci-fi novel When Worlds Collide. Astronomers discovered two bodies in company with each other (orbiting each other? not really stated that way) entering the solar system on a course that would take them very near Earth; eventually it was discerned that they were planets, one a gas giant and the other Earth-sized. Somehow they had lost touch with their own sun & thus become footloose & fancy free; having traveled a very long way they decided to settle in around ours, with the gas giant shortly to take out Earth along the way.

How exactly did the two planets escape intact from their original sun? This being fiction, authors Philip Wylie and Edwin Balmer did not require much in the way of details to set up their plot. Here's the character of the lead scientist explaining things to the character of the action hero:

"Among the many billions of stars, there are probably millions of suns with planets. It is always possible that some catastrophe would tear the planets away. It would require nothing more than the approach of another star toward the sun to destroy the gravitational control of the sun over the Earth and Venus and Mars and Jupiter and other planets, and to send them all spinning into space on cold and dark careers of their own. This world of ours, and Venus and Mars and Jupiter and Saturn, would then wander through indefinite ages - some of them eternally doomed to cold and darkness; others might, after incalculable ages, find another sun."​

 

[rkolter]

If the sun suddenly disappeared, we wouldn't know it for about eight minutes because that's how long it would take the light to travel the distance between the sun and the earth.

But I've often wondered; if the sun suddenly disappeared, would the Earth continue in its orbital path around the sun for eight minutes, or would it immediately fly off into outer space, off its orbital path around the sun, the instant that the sun disappeared?

Does gravity travel at the speed of light? I guess we won't know the answer to this question until we figure out what gravity is.

We experience the Sun as it existed about 8 minutes ago as you said, because it takes that long for light from the sun to reach us. Nothing travels faster than the speed of light. So if the sun vanished at this moment, we would continue to see the Sun until the information that it vanished reached us. Gravity most probably travels at the speed of light. But if it didn't it could only move slower (not faster) than light so minimally yes, the Earth would orbit the Sun so long as the Sun remained in our sky.

If you could hover above the solar system and watch all this play out, this is what you would see:
00:00 The sun vanishes! Someone has some explaining to do.
03:13 Mercury stops reflecting sunlight and stops orbiting the point where the sun used to be.
06:00 Venus stops reflecting sunlight and stops orbiting the point where the sun used to be.
08:19 Earth stops reflecting sunlight ands tops orbiting the point where the sun used to be. At the same time that we stop seeing the sun, we also note that Mercury and Venus are not reflecting light from the sun.
...T+1.3 seconds - Moon stops reflecting sunlight
12:40 Mars stops reflecting sunlight and stops orbiting the point where the sun used to be.
...T+3 minutes 21 seconds - From Earth, Mars stops reflecting sunlight
43:20 Jupiter stops reflecting sunlight and stops orbiting the point where the sun used to be.
... T+34 minutes 1 second - From Earth, Jupiter stops reflecting sunlight

... and so on. Neptune would reflect the sun for 4.1 hours after it vanished - about 4 hours after the Earth left its orbit. Voyager 1, out past the heliopause, would note the sun vanished about 17.5 hours later.

 

[jbriggs444]

At the same time that we stop seeing the sun, we also note that Mercury and Venus are not reflecting light from the sun.
...T+1.3 seconds - Moon stops reflecting sunlight

Assuming, of course, that this takes place during a conjunction when Mercury, Venus, Earth and Moon are all nicely lined up.

[Which makes it hard to see the reflected light from Mercury and Venus]

 

[rkolter]

Assuming, of course, that this takes place during a conjunction when Mercury, Venus, Earth and Moon are all nicely lined up.

[Which makes it hard to see the reflected light from Mercury and Venus]

Fair enough - the T+plus values assume the planets are on this side of the sun and fairly closely aligned with Earth. If they were elsewhere in their orbits, the times I gave for when they would lose sunlight would still be right, but how long they might reflect the sun from the Earth's viewpoint would change. Even for the Moon, if it were out in front of the Earth at the time, it would stop reflecting sunlight just before, not after, the sun vanished from our skies.

But then again, we are allowing for the instant removal of the SUN. Is it really that far fetched to say that the planets are where we want them to be in their orbits? The OP did not state when this would happen, only that it did happen. :P

 

[jbriggs444]

The OP did not state when this would happen, only that it did happen. :P

Yup, fair enough.

 

[Vanadium 50]

One of the things I dislike about these threads is they layer counterfactual on top of counterfactual.

Under no circumstances do you get information that the sun has stopped shining from reflected light (from the moon or planets) than direct sunlight.

Edit: than --> sooner than or faster than

 

[rkolter]

One of the things I dislike about these threads is they layer counterfactual on top of counterfactual.

Under no circumstances do you get information that the sun has stopped shining from reflected light (from the moon or planets) than direct sunlight.

You mean the Moon. Yeah. It was the end of the day. My bad and you're right.

There is no way for light being reflected from the Moon (Venus or Mercury) to reach us before or even precisely when the initial information the sun went out reaches the Earth. And for the planets further out my "T+" times are half the actual time in a best case scenario - because the reflected light has to travel back to us - so if the information about the sun disappearing hit Mars 3 minutes 21 seconds after the Earth, the Earth would see Mars continue to shine for 6 minutes, 42 seconds - 3 minutes 21 seconds for Mars to know, and 3 minutes 21 seconds for Mars to inform us.

Better?