<p>It would take MUCH longer. A push is communicated at the speed of sound inside the medium. Within solid materials that's typically a few km/s, not the speed of light at 300.000km/s. Thus it is about 100.000 times slower, and it would take about a year for this sound wave to travel through this rod from here to the Sun.</p>

CC BY-SA 4.0
2022-09-09T09:26:03.937Z
Has this been experimentally confirmed in any way, though?
White Prime
CC BY-SA 4.0
2022-09-09T09:32:36.423Z
Are you asking whether sound waves and their propagation speed have been measured?
planetmaker
CC BY-SA 4.0
2022-09-09T11:42:37.097Z
You know very well that's not what I'm asking, mate.
White Prime
CC BY-SA 4.0
2022-09-09T13:39:56.233Z
Honestly, no, I don't. I'm really not sure what you are asking for in your comment, other than speed-of-sound measurements. Because here on Earth we have these kind of measurements daily: an earthquake is nothing different than something pushing on Earth. And we do feel the quake in Japan only many minutes or few hours later here in Europe
planetmaker
CC BY-SA 4.0
2022-09-10T11:51:27.950Z
I meant has there been any experiments with long objects that can in any way, however miniscule due to the obvious practical limitations, prove it?
White Prime
CC BY-SA 4.0
2022-09-11T17:21:04.737Z
@WhitePrime - The speed of sound is, by definition, the speed at which a pressure change at one end of a medium (a push) transfers through the medium.  The speed of sound in various solid objects has been measured a number of times; the largest such object is probably the earth, where the speed of sound through various parts of the earth has been measured seismologically.
antlersoft
CC BY-SA 4.0
2022-09-13T09:26:21.653Z
@antlersoft But this isn't a case of a wave travelling from one place to another. The rod is physically there. The work has been done.
White Prime
CC BY-SA 4.0
2022-09-09T09:04:22.770Z
2022-09-09T09:04:22.770Z
planetmaker
<p>When I hang a basket on a rope of one AU long to get my groceries up in my air-castle, the rope can be momentarily one meter longer when I pull the rope one meter up. Likewise, the stick gets compressed when I push it one meter ahead of me. A wave of increased mass travels along the stick with the speed of sound and when that arrives on the other end, the stick jumps to its original length, as the rope does when I pull it up one meter. So it can take some time to pull in my groceries. The fruit in my basket will be wasted before it arrives... no matter how hard I pull the rope in.</p>

CC BY-SA 4.0
2022-09-09T22:27:39.647Z
2022-09-09T22:27:39.647Z
Gerald
<p>They would say, of course, that because nothing can be allowed to transmit faster than light, it would take 8.20 minutes for the fellow at the other end of the rod to feel the push.</p>
<p>But wouldn't the <em>work have already been done</em>? The rod is there. It's the same concept for why gravity can 'escape' a black hole.</p>
<p>If we set up this experiment, when the rod was pushed forward, it seems to me the fellow at the other end would immediately feel it.</p>
<p>Do all the atoms in the rod really have to compress and transfer all the way to the other end? To avoid faster-than-light information transference?</p>
<p><strong>EDIT</strong> @planetmaker has just pointed out it is far, far worse than I thought. The push would actually take an entire <em>year</em> to feel since apparently it would move at the speed of sound.</p>

CC BY-SA 4.0
2022-09-09T12:10:35.697Z
I'd politely suggest to perhaps revise your writing style to be a bit less aggressive/editorial, you might get some better responses.
user438383
CC BY-SA 4.0
2022-09-09T12:29:15.720Z
@user438383 I don't at all mean to come across as aggressive, for what it's worth.
White Prime
CC BY-SA 4.0
2022-09-10T09:38:39.030Z
*"You genuinely believe all the atoms in the rod have to compress and transfer all the way to the other end?"* Are you proposing some alternative to that? Atoms move according to the laws of physics, not magic.
PM 2Ring
CC BY-SA 4.0
2022-09-10T09:41:35.143Z
@PM2Ring Do you genuinely think it would an entire *year* for the fellow at the other end to feel/see the rod move?
White Prime
CC BY-SA 4.0
2022-09-10T09:47:37.400Z
@WhitePrime Of course. Why do you ask if I *genuinely* think that?
PM 2Ring
CC BY-SA 4.0
2022-09-10T10:23:45.120Z
Note that planetmaker said "about a year". Using data from https://www.engineeringtoolbox.com/sound-speed-solids-d_713.html it'd take ~299 days for stainless steel, and only ~144 days for diamond, if the rod's at room temperature.
PM 2Ring
CC BY-SA 4.0
2022-09-10T11:47:16.857Z
@PM2Ring That is interesting extra information.
White Prime
CC BY-SA 4.0
2023-09-26T14:40:23.530Z
A rigid rod, like a massless string, does not exist.
ProfRob
<astrophysics>
How long would it take a rigid rod from Earth to the Sun to move if pushed?
White Prime
# How long would it take a rigid rod from Earth to the Sun to move if pushed?

(Asked by: username_0 on 2022-09-09)

They would say, of course, that because nothing can be allowed to transmit faster than light, it would take 8.20 minutes for the fellow at the other end of the rod to feel the push.

But wouldn't the *work have already been done*? The rod is there. It's the same concept for why gravity can 'escape' a black hole.

If we set up this experiment, when the rod was pushed forward, it seems to me the fellow at the other end would immediately feel it.

Do all the atoms in the rod really have to compress and transfer all the way to the other end? To avoid faster-than-light information transference?

**EDIT** @planetmaker has just pointed out it is far, far worse than I thought. The push would actually take an entire *year* to feel since apparently it would move at the speed of sound.

**Tags:** astrophysics
> **Comments:**
> **username_1**: I'd politely suggest to perhaps revise your writing style to be a bit less aggressive/editorial, you might get some better responses.  
> **username_0**: @user438383 I don't at all mean to come across as aggressive, for what it's worth.  
> **username_2**: *"You genuinely believe all the atoms in the rod have to compress and transfer all the way to the other end?"* Are you proposing some alternative to that? Atoms move according to the laws of physics, not magic.  
> **username_0**: @PM2Ring Do you genuinely think it would an entire *year* for the fellow at the other end to feel/see the rod move?  
> **username_2**: @WhitePrime Of course. Why do you ask if I *genuinely* think that?  
> **username_2**: Note that planetmaker said "about a year". Using data from https://www.engineeringtoolbox.com/sound-speed-solids-d_713.html it'd take ~299 days for stainless steel, and only ~144 days for diamond, if the rod's at room temperature.  
> **username_0**: @PM2Ring That is interesting extra information.  
> **username_3**: A rigid rod, like a massless string, does not exist.  

---

## 2 answers

### Answer by username_4 on 2022-09-09. Score: 6 | Accepted answer

It would take MUCH longer. A push is communicated at the speed of sound inside the medium. Within solid materials that's typically a few km/s, not the speed of light at 300.000km/s. Thus it is about 100.000 times slower, and it would take about a year for this sound wave to travel through this rod from here to the Sun.

> **Comments:**
> **username_0**: Has this been experimentally confirmed in any way, though?  
> **username_4**: Are you asking whether sound waves and their propagation speed have been measured?  
> **username_0**: You know very well that's not what I'm asking, mate.  
> **username_4**: Honestly, no, I don't. I'm really not sure what you are asking for in your comment, other than speed-of-sound measurements. Because here on Earth we have these kind of measurements daily: an earthquake is nothing different than something pushing on Earth. And we do feel the quake in Japan only many minutes or few hours later here in Europe  
> **username_0**: I meant has there been any experiments with long objects that can in any way, however miniscule due to the obvious practical limitations, prove it?  
> **username_5**: @WhitePrime - The speed of sound is, by definition, the speed at which a pressure change at one end of a medium (a push) transfers through the medium.  The speed of sound in various solid objects has been measured a number of times; the largest such object is probably the earth, where the speed of sound through various parts of the earth has been measured seismologically.  
> **username_0**: @antlersoft But this isn't a case of a wave travelling from one place to another. The rod is physically there. The work has been done.  

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### Answer by username_6 on 2022-09-09. Score: 1

When I hang a basket on a rope of one AU long to get my groceries up in my air-castle, the rope can be momentarily one meter longer when I pull the rope one meter up. Likewise, the stick gets compressed when I push it one meter ahead of me. A wave of increased mass travels along the stick with the speed of sound and when that arrives on the other end, the stick jumps to its original length, as the rope does when I pull it up one meter. So it can take some time to pull in my groceries. The fruit in my basket will be wasted before it arrives... no matter how hard I pull the rope in.


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