Author Topic: would you stop the world from turning?  (Read 3957 times)

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Online hamster_nz

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would you stop the world from turning?
« on: June 18, 2015, 08:11:50 am »
What if you invented a technique to convert Earth's orbital momentum into usable energy with very low efficiency, would you be OK with it being used, knowing that eventually it must lead to the planet's demise as it spirals in to the Sun.

What if the demise would take a billion years? A million? a thousand?

How would that change if you reflect on the fact that some day somebody else will invent it? or others are already be covertly using it?

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Offline AndyC_772

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Re: would you stop the world from turning?
« Reply #1 on: June 18, 2015, 08:54:22 am »
I'd be more worried about where the remaining energy was going, if the process was inefficient.

Something, somewhere, would be getting very hot indeed.

Offline miguelvp

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Re: would you stop the world from turning?
« Reply #2 on: June 18, 2015, 09:02:21 am »
I thought that tidal power plants already did that, but no more than the tides eroding the coast lines to begin with.
 

Offline Mechanical Menace

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Re: would you stop the world from turning?
« Reply #3 on: June 18, 2015, 01:03:58 pm »
It's happening anyway, just so slowly the sun will die before the Earth's orbit degrades majorly.

Reducing how long the orbit can stay in roughly the same place by a billion years would still leave billions of more years longer than the system has.
« Last Edit: June 18, 2015, 01:05:32 pm by Mechanical Menace »
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Offline retrolefty

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Re: would you stop the world from turning?
« Reply #4 on: June 18, 2015, 01:09:56 pm »
No thanks. There doesn't need to be another bullet point for the global warming nuts to rage against.

 

Offline HighVoltage

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Re: would you stop the world from turning?
« Reply #5 on: June 18, 2015, 02:01:23 pm »
Our time has to be adjusted every once in a while, because the earth is already slowing down.
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Offline Deathwish

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Re: would you stop the world from turning?
« Reply #6 on: June 18, 2015, 02:07:14 pm »
Yes, but only so I could make all the politicians get off and push us round in orbit. Then again I want to live on an island in a windmill so I must be mad anyway.
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Online PA0PBZ

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Re: would you stop the world from turning?
« Reply #7 on: June 18, 2015, 02:08:27 pm »
Our time has to be adjusted every once in a while, because the earth is already slowing down.

Isn't that something like 2mS per century? Time correction is more likely necessary because our day isn't exactly 24 hours.
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Offline HighVoltage

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Re: would you stop the world from turning?
« Reply #8 on: June 18, 2015, 02:50:37 pm »
Isn't that something like 2mS per century? Time correction is more likely necessary because our day isn't exactly 24 hours.

http://derstandard.at/1339639363732/Zeit-Korrektur-Dem-heurigen-Jahr-wird-eine-Sekunde-geschenkt

Looks like they added 25 times "one second" since 1972.
There is also an international institution, that takes care of this, the IERS (International Earth Rotational Service?)
And their suggestion was to stop the adding of seconds and wait until the year 2600 and add one full hour.

 
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Offline Lightages

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Re: would you stop the world from turning?
« Reply #9 on: June 18, 2015, 04:08:08 pm »
Not that it is that important, but the OP was talking about the ORBITAL motion of the Earth around the sun, not the rotation of the Earth.
 

Offline AndyC_772

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Re: would you stop the world from turning?
« Reply #10 on: June 18, 2015, 04:35:42 pm »
In rough figures...

Mean orbital velocity of Earth = 29800m/s

Kinetic energy per kg of planet = 1/2 * 1 * v^2 = 444e6 J

Specific heat capacity of many common rocks and metals, to within an order of magnitude, are around 800 J/kg/C.

So, the approximate temperature rise which would have to happen to the planet if the kinetic energy associated with the Earth's orbit were converted into useful forms, and ultimately into heat, would be:

444e6 / 800 = 555,000 deg C

So no, I wouldn't be concerned about falling into the Sun. We'd all be plenty warm enough well before that happened  ;D

Offline Mechanical Menace

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Re: would you stop the world from turning?
« Reply #11 on: June 18, 2015, 05:15:45 pm »
...

But (in probably even rougher figures) we'd only need around 0.00009 J/kg (so lets say 0.0001-3 J/kg to have a utopian abundance) of the planet to produce all the energy we use, wish I could be arsed working out what reduction in orbital velocity that'd need to produce lol
« Last Edit: June 18, 2015, 05:23:42 pm by Mechanical Menace »
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Offline T3sl4co1l

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Re: would you stop the world from turning?
« Reply #12 on: June 18, 2015, 06:34:53 pm »
Another back-of-the-envelope calculation:

Total solar insolation is 42 PW, about half of which is absorbed as heat in the atmosphere and at the surface (and ultimately re-radiated as infrared).

Suppose that an increase by 3% would be sufficient to cause cataclysmic warming (i.e., raising mean temperature from 288K to 298K).  Presumably, that would require about 3% more heat.

So our budget is 3%, or 1.26 PW.  According to https://en.wikipedia.org/wiki/World_energy_consumption, the entire year of 2012 used 5.6 x 10^20 J, or 18 TW average.  Humanity has about two orders of magnitude to go before running into climate problems by brute force alone (i.e., not counting greenhouse gasses and such).

FWIW, at present exponential growth rate, energy use (fuel, thermal, electric, everything) should take about 250 years, i.e., by about year 2260, to reach that level.

A change of 3% insolation also corresponds to an average 1.5% closer orbit.  (The halving comes from the inverse-square law: for small changes in r, the change in power goes as -2 dr / r.)

Suppose we were able to shift our energy demands into pure orbital energy.  Suppose we used as much as possible, to maximize power use without absolutely destroying the climate (i.e., maintaining that 3% power gain, steady).

Rather than exponential growth, this would have an inverse exponential curve, because as we use more orbital energy, the Earth moves closer, and more insolation means less margin for direct power use.

The Earth has a potential-kinetic energy of 2.7 x 10^33 J.

The required annual change is initially 1 x 10^19 J.  This rate could be held until the orbit decays that 1.5%, that is when 1.5% or 4 x 10^31 J of the potential energy has been used.  This would take about 4 x 10^12 years to consume; but because it must decay exponentially, it will actually drop faster than that, at a time constant of 11 x 10^12 years (I think).

Did I do that backwards or anything?

If it truly is on the order of trillions of years, then over the next two billion, we will have to contend with solar instability.  Assuming the Earth (and any intelligence on it) survives that long, it may be sufficient to ride out our gravitational potential energy for quite a long time; indeed, once the Sun shrinks to a white dwarf (which itself will give off quite a bit more intensity than it does today, and for a much longer time), and gradually cools off, this would be a fine option, in combination with, say, solar shades for controlling planetary climate.

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Offline helius

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Re: would you stop the world from turning?
« Reply #13 on: June 18, 2015, 06:57:53 pm »
How do we sleep while our beds are burning?
 

Online TerraHertz

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Re: would you stop the world from turning?
« Reply #14 on: June 19, 2015, 04:56:35 am »
First question would be, what's the Sun's projected energy output profile over the next million years?
A: We have no freaking idea. We only know the Sun is a somewhat variable star, and it's output varies over geological time scales quite a bit. With some kinds of patterns showing in what little data we have, but no clue about reasons why.

So, maybe a slight slow orbital radius reduction could be a good thing. Or bad. No way to tell.

I'd say no.

Though, it's a very good bet that humans (as such) won't be here to worry about such things for even a measly million years.
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