These were incomplete comments about a video about "Starlift" that was suggested. I added a few things, but it's nowhere complete as a review of the video.
Why Starlift?
Hydrogen
Other elements
Create heavy elements by transmutation (Star does it?)
Extend the star's lifetime
Decrease the star's brightness
Make new stars
Prevent stars from exploding
"Create heavy elements by Transmutation" -- How do we create the heavy elements? We do it by Transmutation. What is "Transmutation"? It's the process of turning one type of nucleus into another. Something's circular about that, apart from being totally uninformative.
The narrator appeared to get things right somehow or other, yet I couldn't help sensing that things were horribly wrong. He seemed to slip things over on us, slipping over (and omitting) critical aspects. I concluded that as one primary error, he lacked any sense of scale.
I only watched the first few minutes, and had to rewatch to recall certain things. I noticed 23 or 27 minutes left. I didn't want to watch the whole thing.
Comments
What Video?
What video are you talking about? Sounds interesting.
“When a clown moves into a palace, he doesn’t become a king. The palace becomes a circus.” - Turkish Proverb
Suggested by "Suppose"
This was suggested in the forum post, "Suppose".
https://www.youtube.com/watch?v=pzuHxL5FD5U
"Isaac Arthur is a futurist who has produced hundreds of hours of extremely interesting videos and published them on Youtube. The title of this one is `Star Lifting'". As you can see, I had a more negative reaction to my first view of his work.
-- Daphne Xu
Mining Jupiter for Hydrogen
There was one brief passage, where the narrator mentioned mining Jupiter for hydrogen, to be used in fusion -- good until Jupiter ran out of hydrogen. The passage raised so many issues, that the narrator silently shoved past. The narrator had no sense of scale here, and possibly no knowledge of fusion.
A decade or so ago, there was talk of the "hydrogen economy" -- based on chemically burning hydrogen, not fusion. I posed the questions, "Where is the nearest reservoir of elemental hydrogen?" and "Where is the second nearest reservoir?"
Now consider the hydrogen used for fusion. It's no secret that nobody here on earth, involved with fusion energy research, considers straight proton-proton fusion. This is the primary reaction in the center of the sun, under the huge pressure that balances the weight of the sun. (The temperature is considerably cooler than earth-human fusion, but still incredibly hot -- about ten million degrees Kelvin.) Try guesstimating the energy produced every second by one cubic meter inside the core of the sun, say one-tenth the sun's radius.
In order to have any concept of fusion, one must know the basics: how small a nucleus is, the repulsive force between two charged particles, perhaps comparison with the sizes involved in chemistry, knowing what is meant by "inverse-square"*, and so forth. (Force and potential energy help, as well.) A little knowledge of the nuclear force helps as well. (It holds the nucleus together. One should figure out that it's much stronger than the electric force. It also applies equally to both protons and neutrons, which are considered two states of the nucleon.)
*This automatically excludes anyone who talks or writes about an "inverse-square force" that increases the farther one gets from the source. Admittedly, the problem with the book may have been "continuity" -- by the time he got to writing about the force increasing with distance, he'd forgotten that he'd described it as an "inverse-square" force. Editing and revision missed the inconsistency.
Deuterium-tritium fusion is the most considered, and is used in thermonuclear bombs. It's also the easiest mode of fusion. Deuterium-deuterium is considerably harder. Tritium-tritium is harder still. With sufficient basic knowledge, this becomes a puzzle: why is tritium-tritium fusion harder than deuterium-deuterium fusion?
Knowledge of the deuterium nucleus leads to the qualitative answer to that question, but it leads to another question. Why is proton-deuterium fusion not considered? Especially when we consider helium3-helium3 fusion, proton-lithium7 fusion, and proton-boron11 fusion -- where it's so much harder to get the two nuclei close enough together -- are all considered? (Again, there is an answer, that might depend on more advanced knowledge.)
Now, does one realize how much got buried in that short passage about mining Jupiter for hydrogen, for fusion? (Finally, how long would it really take for Jupiter to run out of hydrogen?)
-- Daphne Xu
Star lifting
I saw the video. I'm one of the denizens that watches all of the Science and Futurism with Isaac Arthur videos. I also hang out on the SFIA Facebook page, and have even earned the little coffee cup a few times.
Isaac mentions transmuting hydrogen as a kind of side issue. There are plenty of metals
*in our sun. If that weren't the case, we wouldn't have any rocky planets or asteroids in our solar system. In fact, if we want more building materials and less hydrogen, we can just send the hydrogen back into the sun.The SFIA channel goes into a lot of really far out subjects. It tends to steer away from things that have no basis in known physics, like FTL, but doesn't shy away from things like putting a shell around a black hole and colonizing it, moving the planet, moving the sun, and huge things like that.
In fact, one of Isaac's comments that moving a planet is relatively easy (compared to some of the other stuff he has mentioned) has become somewhat of a meme on the FB group.
* In astrophysics, everything that isn't hydrogen or helium is a metal.
An Ironic Meme?
"In fact, one of Isaac's comments that moving a planet is relatively easy (compared to some of the other stuff he has mentioned) has become somewhat of a meme on the FB group." I hope that the meme is ironic.
One might think, perhaps, that it's easier for a 10yo boy to walk from Houston to Dallas in one hour than from Houston to NYC in one hour. But actually it's not. They're both equally impossible for the 10yo boy.
Likewise, I'm going to go out on a limb and say that moving a planet (say Mercury's size or larger) is impossible. You can't grab onto it with something physical. You either just dig through the planet's material, or (more likely) break your equipment -- the planet's trajectory doesn't change. A non-contact force such as gravity? Well, one needs to move in something comparably massive and move it in the right direction, in order to direct the planet. To solve the problem, we have to have solved the problem.
So is someone going to argue that we don't know what we'll discover in the future? Maybe I'm just being arrogant? We just might happen to discover something in the future?
I've thought of writing a rant (specifically refering to science) about "being right for the wrong reason" vs. "being wrong for the right reason". I'll just say for now that whoever discovers a way to move a planet will be an expert in the field who was initially wrong for the right reason -- at least he's an expert in the field. That's the only type of person who will discover the loophole or the new method.
-- Daphne Xu
moving a planet?
Is a relatively simple process when you think about it. It's held in place in its orbit by gravity of the sun being too strong for the planet's forward momentum to allow it to continue to moving in a straight line. And of course the planet's forward momentum keeps the sun's gravity from pulling it into the sun.
Therefore it's simple physics to change the planet's orbit. Decrease the speed and or increase the planet's mass and it would move closer to the sun, increase the speed and or reduce the planet's mass and it will move further away form the sun. We've been doing it for years with smaller objects that orbit Earth, (satellites and manned spacecraft.)
Mathematically it's entirely possible. Where it becomes ,em>'Not presently' feasible is in applying the required force to make one of these changes. So he was correct in stating it was easier than constructing something like an FTL drive which we don't even have an idea of how to build.
How could you move a planet? Place a massive rocket engine with OMG thrust on the equator and run it only in the planet's reveloution when the engine is facing the proper direction to either slow or speed up the planet. Can we build an engine this powerful right now? Of course not, being possible doesn't mean something is practice but it does mean it is not impossible.
We the willing, led by the unsure. Have been doing so much with so little for so long,
We are now qualified to do anything with nothing.
Actually...
Moving a planet is relatively easy using known physics. The catch is that it is a reaaaaaly sloooooow process. Not hundreds or even thousands of years. More in the millions.
You do it with a gravitational tractor. If you send an object 1/1000000000 of the mass of Earth in a hyperbolic trajectory (like that extrasolar asteroid that went around the sun and flew back out into interstellar space) around the Earth, it will impart velocity equal to 1/1000000000 of the delta vee of the object. The idea of doing it over and over again.
Like I said, it's slow. But it'll get us away from the sun as it turns into a red giant.
Of course, the other way is to move the sun and let the sun drag us along. You do that by putting up a bunch of stattites (mirrors that are held aloft by the pressure of the light) around one side and reflect all of the light in one direction. This is called a Shkadov Thruster. There are a few other variations on that scheme.
So, compared to moving the entire solar system, moving a planet is relatively easy.
Another guestimation
Millions of years, for the "gravitational tractor" method, is about right, if you want to boost the orbit's radius by about 1%. Each pass boosts the earth's speed by about a tenth of a millimeter per second. The mass would have to be somewhere near the dinosaur-killing impactor's, or 6x1015 kg.
-- Daphne Xu
Blast part of the earth in one direction...
... and you'll accelerate the rest of the earth in the opposite direction. Not to mention obliterating the earth.
"Place a massive rocket engine with OMG thrust on the equator and run it only in the planet's revolution when the engine is facing the proper direction to either slow or speed up the planet."
Imagine building an up-side-down rocket -- the one with OMG thrust -- on the earth and firing it into the earth. How far down does it bury itself? How much of the earth does it blast away in the process?
You can't just scale up what we do with a rocket, because the rocket material can withstand the stress (force per unit area, similar to pressure). The earth (and any matter made of atoms) can't withstand the stress required to deflect the earth a significant amount.
https://en.wikipedia.org/wiki/Chicxulub_crater
https://en.wikipedia.org/wiki/Chicxulub_impactor
I very roughly gestimated that the impactor that destroyed the dinosaurs shifted the earth's velocity by about a millimeter per second -- and I'm surprised it was that much. (My answer is plus-minus a couple orders of magnitude.) The impactor devastated the earth's surface. Once the OMG thrust rocket buries itself into the earth, if it still works it blasts rock away.
https://en.wikipedia.org/wiki/Giant-impact_hypothesis -- the Mars-sized planet that hit the earth, ultimately forming the moon, no doubt shifted the earth's orbit significantly. It also smashed the earth.
"Decrease the speed and or increase the planet's mass and it would move closer to the sun." I hope that you are aware that the gravitational acceleration of the earth is independent of its mass. (The force is proportional to the mass.)
-- Daphne Xu