# Physical Interactions over Great Distances

In summary, the conversation discusses a hypothetical scenario in which a long, sturdy rod made of unobtanium is pushed by one astronaut towards another astronaut on the opposite end. The question is whether the other astronaut would see the rod move instantaneously or if there would be a delay. It is explained that the "push" would travel at the speed of sound in the rod, not at the speed of light. The significance of the rod's mass is also discussed, with the conclusion that a smaller mass would make it easier for the astronaut to push the rod. Additionally, a similar scenario using rockets is mentioned for further reading.
Say you (somehow) constructed a very long, sturdy rod, about a light year in length. Say it was made of unobtanium, so it has the same mass as a relatively short steel rod. Now say there are two astronauts, one at each end, and one of the astronauts gives the rod a firm push in the direction of the other astronaut.

Does the other astronaut instantaneously see the rod move in his direction? If not, how exactly does the rod behave? (Does it move at all when the astronaut pushes on it? Or does it take a really long time to start moving?)

Does the other astronaut instantaneously see the rod move in his direction?
No.
If not, how exactly does the rod behave? (Does it move at all when the astronaut pushes on it? Or does it take a really long time to start moving?)
The "push" moves along at the speed of sound in the rod--nowhere near the speed of light, much less instantaneously.

Can you explain the significance of the mass of the rod in your question?

Thanks for the quick re-direct, Doc Al. I had been feeling so proud of myself for thinking up the idea all on my own, but am now humbled to see that the exact same idea was brought up a few short weeks earlier.

country boy -- my thinking was that if it didn't have a small mass, it would have a huge inertia and would be virtually impossible to push by an astronaut anyway.

country boy -- my thinking was that if it didn't have a small mass, it would have a huge inertia and would be virtually impossible to push by an astronaut anyway.

I see. You might be interested in this thread also, which uses rockets to propel a rod:

## What is meant by "Physical Interactions over Great Distances"?

"Physical Interactions over Great Distances" refers to the phenomenon where objects or particles can affect each other despite being separated by large distances. This can occur through various physical forces, such as gravity, electromagnetism, or the nuclear force.

## How do physical interactions over great distances occur?

Physical interactions over great distances occur through the exchange of particles or fields between objects. For example, gravitational interactions occur through the exchange of gravitons, while electromagnetic interactions occur through the exchange of photons.

## What are some examples of physical interactions over great distances?

Some examples of physical interactions over great distances include the gravitational pull between celestial bodies, such as planets and stars, the magnetic field of the Earth affecting compass needles, and the nuclear forces that hold atoms together.

## Can physical interactions over great distances be explained by traditional physics?

Yes, physical interactions over great distances can be explained by traditional physics theories, such as Newton's laws of motion, Maxwell's equations, and quantum mechanics. These theories have been extensively tested and have been found to accurately describe the behavior of physical interactions over great distances.

## What are the potential applications of understanding physical interactions over great distances?

Understanding physical interactions over great distances can have many practical applications. For example, it can help us better understand and predict the behavior of celestial bodies, improve communication and navigation technologies, and guide the development of new technologies, such as quantum computing.

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