# Thread: Can work be extracted from the expansion of the universe?

1. Richard Feynman originally came up with the stick bead argument to show that gravitational waves contain energy, and I could be wrong but it seems to me it can also show that work could be extracted from the expansion of the universe. Place a bead on a sticky rigid rod, atomic forces will keep the distance between the 2 ends of the rod constant but the proper distance between between the bead and the ends of the rod will change do to the expansion of the universe. If the rod is sticky then there will be friction and relative motion between the rod and the bead will produce heat. And if you have heat you can run a steam engine and get work out of it. I know the effect would be very very very small, I just want to know if I understand the concepts correctly.

John K Clark

2. Originally Posted by John K Clark
Richard Feynman originally came up with the stick bead argument to show that gravitational waves contain energy, and I could be wrong but it seems to me it can also show that work could be extracted from the expansion of the universe. Place a bead on a sticky rigid rod, atomic forces will keep the distance between the 2 ends of the rod constant but the proper distance between between the bead and the ends of the rod will change do to the expansion of the universe. If the rod is sticky then there will be friction and relative motion between the rod and the bead will produce heat. And if you have heat you can run a steam engine and get work out of it. I know the effect would be very very very small, I just want to know if I understand the concepts correctly.

John K Clark
Expansion pertains to increasing distance between points in spacetime. It does not pertain to increasing distance between points belonging to objects. Objects do not expand.

3. Originally Posted by AndrewC
Expansion pertains to increasing distance between points in spacetime. It does not pertain to increasing distance between points belonging to objects. Objects do not expand.

I know. The atomic forces between the atoms of the rod keep it from expanding. The bead does not expand either and for the same reason, but if the universe is expanding then the bead should moves relative to the ends of the rod, and the friction between the two should cause heat. Feynman used this example to show that gravitational waves contain energy, if it shows that gravitational waves contain energy I don't see why it wouldn't also show the work can be extracted from the expansion of the universe. If my reasoning is incorrect I wish somebody would pinpoint where the error is. Why can you extract work from gravitational waves but not from the expansion of the universe?

John K Clark

4. Originally Posted by John K Clark
I know. The atomic forces between the atoms of the rod keep it from expanding. The bead does not expand either and for the same reason, but if the universe is expanding then the bead should moves relative to the ends of the rod,
No, it DOESN'T. Please stop pushing fringe ideas, this is a mainstream physics forum.

I don't see why it wouldn't also show the work can be extracted from the expansion of the universe.
Because they are DIFFERENT phenomena.

Why can you extract work from gravitational waves but not from the expansion of the universe?
Because mechanical work implies OBJECT MOTION. There is no object motion in the universe expansion. In the latter it is only the space between objects that expands.

5. I'm not trying to push ideas I'm just asking questions so I can understand. In the case of gravitational waves the space between objects osculates and work can certainly be extracted from that; Dark Energy causes the space between objects to expand and even accelerate and I'm confused as to why you can't get work from that too. My intuition, which I admit is probably wrong, tells me it should be even easier to get work out of something that moves in one direction than from something that osculates. Where did I go wrong?

John K Clark

6. Originally Posted by John K Clark
Where did I go wrong?

John K Clark
I already explained that to you, three times. Here is another explanation: the work is defined as where F is the force exerted. There is no force in the universe expansion.

7. So to produce oscillations in spacetime a force is required and work can be extracted but to produce a expansion of spacetime a force is not required and no work can be extracted??

John K Clark

8. Originally Posted by John K Clark
So to produce oscillations in spacetime a force is required and work can be extracted but to produce a expansion of spacetime a force is not required and no work can be extracted??

John K Clark
You finally (maybe) got it.

9. Andrew, you're acting like I asked a stupid question but I did not. I finished high school physics a long time ago so I already knew that work is force over distance and didn't need you to tell me. What I asked was how expanding spacetime back and forth, as gravitational waves do, can produce work but expanding spacetime in just one direction, as the expanding universe does, can not, it seems completely counter-intuitive.

At this point it is painfully obvious that you don't have the slightest idea how to answer my question, and I don't think you've ever heard of a Black Hole Firewall despite it currently being one of the most intensively researched topic in General Relativity. Perhaps your inability to answer my questions explains your hostility and rudeness. I'll just have to hope I can find the answers elsewhere. Good-by.

John K Clark

10. Originally Posted by John K Clark
Andrew, you're acting like I asked a stupid question but I did not. I finished high school physics a long time ago so I already knew that work is force over distance and didn't need you to tell me.
Good for you, now you hopefully understand why there is no work to be extracted from universe expansion.

What I asked was how expanding spacetime back and forth, as gravitational waves do, can produce work but expanding spacetime in just one direction, as the expanding universe does, can not, it seems completely counter-intuitive.
Tough.

At this point it is painfully obvious that you don't have the slightest idea how to answer my question,
I gave you two differenr explanations why you are wrong, you understood neither.