Tachyon Shields Sci Tech Questions Thread

[All Seeing Eye]

I've started this thread because i'm always thinking up Sci Tech questions that I want to ask people about and rather than keep starting new threads up and cluttering the Sci Tech forum, I figured it would be easier, better and more efficient to start one thread for all my questions.

So basically every time I think up a question i'll just post it in here.

My first question for the thread is:

What Would Happen If You Focused A Laser Beam At A Chunk Of Uranium?

If we used this (the facility researching fusion) but we instead focused the laser beams at a chunk of Uranium what would happen?

 

[cultcross]

Nothing. The energy required to initiate fusion in a heavy metal like Uranium would be far higher than that facility can generate.

 

[Asbo Zaprudder]

The result would probably be Uranium vapour or plasma. You'd be better off firing fast neutrons at it -- this is the R-process, which occurs in supernovae and fast breeder reactors.
http://en.wikipedia.org/wiki/Supernova_nucleosynthesis
http://en.wikipedia.org/wiki/Fast_breeder

ETA: or you could try bombarding with much lighter nuclei, such as those of Caesium. These can be used to produce short-lived transactinide element nuclei by bombarding Plutonium, Californium, or Americium. Not sure what happens if you bombard Uranium with them.
http://en.wikipedia.org/wiki/Transactinide_element

 

[TerriO]

And before anyone goes on, he has permission for this to concentrate all his questions in one location without fear of getting nailed for spamming.

 

[All Seeing Eye]

Question 2

You know when you roll out pastry and you use a cutter to slice shapes? well imagine we do something similar to the Moons surface. we dig lines into the moon and create a square or circular shape. Now imagine we dig a hole (or several holes) into it and drop down some Nuclear Weapons and detonate them:

2a) Would the resulting nuclear explosions be enough to cause a large chunk of the Moon to break off and escape the Moons gravity?

2b) Could this chunk of Moon fall towards the Earth and cause mass extinction upon impact?

 

[Asbo Zaprudder]

Yes and yes -- however, it would be easier to use nukes (or your "digger" as a reaction mass driver) to divert an asteroid instead.

 

[Zulu Romeo]

Question 2

You know when you roll out pastry and you use a cutter to slice shapes? well imagine we do something similar to the Moons surface. we dig lines into the moon and create a square or circular shape. Now imagine we dig a hole (or several holes) into it and drop down some Nuclear Weapons and detonate them:

2a) Would the resulting nuclear explosions be enough to cause a large chunk of the Moon to break off and escape the Moons gravity?

2b) Could this chunk of Moon fall towards the Earth and cause mass extinction upon impact?

Despite the reduced mass and gravity of the Moon versus Earth, wouldn't a few nuclear explosions underneath the Moon's surface still have very little effect? I mean, underground nuclear testing on Earth generates the sort of piddling forces that a moderate earthquake or volcano would simply point at and cry with hysterical laughter.

As for breaking off a chunk of the moon, it would still be orbiting the Earth at a different velocity relative to the Moon's orbit and rotation. It could very well orbit the Moon first and even crash onto its surface first if it doesn't achieve the Moon's escape velocity. If it could escape the Moon's clutches, the next influential body wold be the Earth, so in theory it could fall to Earth, but not without several orbits first.

But then again consider that as a result of a sufficiently large explosion causing a chunk of the Moon to break off and escape the Moon's gravity, the velocity and mass of the Moon itself will have also changed (likely a reduction of both) - I'd be more worried by the Moon altering its orbital path, thus altering tidal forces on Earth and causing coastal devastation, etc. long before anything actually hits us.

Dammit, I'm a doctor, not a physicist!

 

[Asbo Zaprudder]

Well, you'd be performing Project Orion with a lump of Moon rather than a spaceship. You'd have the advantage of a much lower escape velocity than on Earth, and no worries about radioactive fallout. Use a few big nukes to mine out your rock, and then drop a few hundred or so small "Davy Crockett"-sized ones to propel it toward Earth. As I said, it would be easier to propel an asteroid that's not sitting in a gravity well.

 

[Asbo Zaprudder]

Nothing. The energy required to initiate fusion in a heavy metal like Uranium would be far higher than that facility can generate.

-- although if you compressed an enriched Uranium pellet into supercriticality, and injected initiator neutrons at the right time, you might have the makings of a fission bomb. However, without an effective tamper, it might well just fizzle out before much fission could take place.

 

[Trekker4747]

Question 2

You know when you roll out pastry and you use a cutter to slice shapes? well imagine we do something similar to the Moons surface. we dig lines into the moon and create a square or circular shape. Now imagine we dig a hole (or several holes) into it and drop down some Nuclear Weapons and detonate them:

2a) Would the resulting nuclear explosions be enough to cause a large chunk of the Moon to break off and escape the Moons gravity?

2b) Could this chunk of Moon fall towards the Earth and cause mass extinction upon impact?

Siiiiigggggggghhhhhhhhhh.

 

[cultcross]

Despite the reduced mass and gravity of the Moon versus Earth, wouldn't a few nuclear explosions underneath the Moon's surface still have very little effect? I mean, underground nuclear testing on Earth generates the sort of piddling forces that a moderate earthquake or volcano would simply point at and cry with hysterical laughter.

Indeed. A small earthquake, the sort only resting non-Californian people feel, releases a lot more energy than our most powerful weapons. And yet the Earth doesn't fracture in two. Our weapons are big on our scale. In cosmological terms, they're spud guns.

 

[Zulu Romeo]

Despite the reduced mass and gravity of the Moon versus Earth, wouldn't a few nuclear explosions underneath the Moon's surface still have very little effect? I mean, underground nuclear testing on Earth generates the sort of piddling forces that a moderate earthquake or volcano would simply point at and cry with hysterical laughter.

Indeed. A small earthquake, the sort only resting non-Californian people feel, releases a lot more energy than our most powerful weapons. And yet the Earth doesn't fracture in two. Our weapons are big on our scale. In cosmological terms, they're spud guns.

I felt one of those "small" earthquakes underneath my bed last February. For a force equivalent to a multi-megaton explosion, I wanted my money back - especially as its epicentre in Lincolnshire survived with only minor damage.

 

[All Seeing Eye]

Question 3:

New method of travelling through space.

3a) If we could create a device that negated the effects of gravity and momentum would a ship in space suddenly remain still in one spot an the solar system and rest of the Galaxy speed past it?

3b) Would a ship be capable of just sitting there in space not moving and simply just wait for the destination star system to come to the ship rather than the ship go to the star system?

 

[Scout101]

Isn't that just a matter of perspective? Whether you move against the force, or sit in once place and let things come to you, you're accomplishing exactly the same thing, and it's just perspective. From the POV of the ship, things are moving towards you, from the POV of the destination, here you come. So what?

 

[All Seeing Eye]

The amount of fuel required to get a ship to 1,188,000mph (the speed of the galactic arms and the speed the Galaxy is travelling through the universe combined) would probably be enormous especially if it's a generational ship. The energy requirement to cancel out gravity and momentum might be less than the fuel required to propel a ship to that speed.

If you cancel out gravity and momentum and you're in the best spot available at the time your destination star system would start travelling towards you at 1,188,000mph. If you're not in the best location at the time then the speed would be reduced, especially if the spiral arm of the galaxy isn't moving in the same direction as the Galaxy through space.

Even if your ship isn't lined up with your desired destination though you could still use the anti-gravity/momentum device to get closer to your destination faster and then switch to conventional travel. It could shave decades/hundreds of years off a journey.

 

[Scout101]

You've completely bypassed the question, as usual. What's the difference? It's just a POV thing, you really aren't changing the basic facts. Moving towards something, vs expending energy to stay still while it comes to you, basically the same thing. Just a matter of where you are observing from.

Your number of 1.188 million MPH is bogus and misleading, anyway. It's not in relation to the object you are moving towards, or point you are leaving from, so including it as an impressively large number doesn't help. By your calculations, I could travel 1,188,005 MPH simply by moving 5 MPH in the same direction as the galactic speed. Doesn't require special engines or magic fuel, a small thrust would get it done. Furthering the POV you're trying to use, moving in one direction through the universe should be simplistic to move at over 1 million MPH, and it should be essentially impossible to move opposite the galactic spin.

ANY of these questions only make sense if you talk about a consistent POV. Can't use one POV to measure speed, another distance, and 3rd to say that you moved, or didn't move.

 

[All Seeing Eye]

Your opinion is noted, thanks.

 

[Arrqh]

It's not an opinion. Velocity is meaningless without a reference frame and one of the tenants of relativity is right there in the name.... there is no such thing as an objective reference frame because it's all relative.

What you're suggesting is some way of sticking an object into this non-existent frame. You say that the galaxy is moving at a certain speed.... that is incorrect. It is moving at that speed relative to everything else that we can measure. But that entire system could be moving at some velocity, perhaps relative to something that we can't measure. Even if there was some sort of objective reference frame, we'd have no way of knowing what it is. So if you take your magical device that can break the laws of physics, you have no idea what speed and direction it would actually move in once is was married to this imaginary objective frame.

 

[Silvercrest]

Another way of looking at it is that nothing is really standing still. If you appear to be standing still with respect to the solar system, the galaxy, etc., that's only a local perspective -- you're still moving with respect to other solar systems, galaxies, and anything else that happens to be traveling a different direction and speed.

So, you may be able to cease your motion with respect to the galaxy or whatever, but that isn't "remaining still in one spot". There is no such thing! You're only stopping as far as your target object is concerned. If a person in a different galaxy sees you, to him you'll still appear to be moving... and he's correct. (Although since you've just changed your velocity, he will still see you speed up or slow down.)

After all, how can you "cancel out momentum with respect to everything", when everything is moving in different directions?

So, if all you're doing is changing your velocity or direction with respect to galactic motion, it comes right back to the issue of how much fuel or energy you have to expend to do it. It takes exactly the same amount to brake yourself with respect to an oncoming galaxy and let it come to you at a certain speed, as it does to accelerate toward the galaxy at the same speed... and that's because these two are the same thing. They're not equivalent concepts, they are the SAME concept.

So, to address your original thought: Even if you line yourself up with an oncoming galaxy and use a magical momentum-canceling device to let the galaxy apparently accelerate toward you, powering that device will take the same amount of energy or fuel as accelerating toward the galaxy with a high-speed engine. Ultimately you're still just trying to accomplish the same thing, so it will take the same amount of energy either way.

 

[All Seeing Eye]

Well I still think it's an interesting idea, if you can manipulate which gravity effects you want to you could basically switch off what effects you want and everything moves towards you in the direction that you want and you don't even move anywhere (in a sense).