UFO sighting in Texas...

[Gafgarionn]

Briane Green's "The Elegant Universe" is possibly one of the best books for getting a non-technical understanding of Quantum Mechanics (and string theory, of course), and anyone who can read BG forums is capable of understanding it.

Yes, and if you have any scientific curiosity whatsoever you'll have a great time reading it.

[Andarvi]

Never paid attention in science or any physics class, reading this thread kinda makes me wish I did.

Shit doesn't seem half as interesting in school.

You should read up on Quantum Mechanics. It's trippier and less intuitive than Relativity.

Telling someone with no physics background to check out quantum mechanics is going to result in a massive wooooooooooooooooooooooooooooosh. I suppose the could read into it in a very, very abstract and conceptual manner. I assume thats what you mean.

I don't know about that. There are plenty of books out there that do a good job of explaining QM. It's definitely not the same as Relativity, since you can brood over Relativity for a bit and at least understand the main concepts. Without ever taking a physics class, I read The Elegant Universe, by Brian Greene. It goes over the foundational concepts behind QM and then explains how it all relates. Obviously it's not going to be as easy as reading Harry Potter or something, but I think the ideas are accessible to anyone that sincerely wants to learn it.

I heard somewhere that if you aren't WTFing constantly while learning QM, you don't understand it. That's probably true.

Yeah thats what I meant.

[Khamsin]

So if a single theory of everything was discovered from which all forces of the universe could be derived, including gravity, would we be able to predict the future? Or would probability clouds fix that?

[Neosutra]

So if a single theory of everything was discovered from which all forces of the universe could be derived, including gravity, would we be able to predict the future? Or would probability clouds fix that?

Sure, we could predict all possible futures, if you woudlnt mind entering in the infinite number of quantum variables into a computer capable of running infinite permutations of each possiblity.

[Kaylia]

So if a single theory of everything was discovered from which all forces of the universe could be derived, including gravity, would we be able to predict the future? Or would probability clouds fix that?

Laplace's demon

[Gafgarionn]

So if a single theory of everything was discovered from which all forces of the universe could be derived, including gravity, would we be able to predict the future? Or would probability clouds fix that?

Sure, we could predict all possible futures, if you woudlnt mind entering in the infinite number of quantum variables into a computer capable of running infinite permutations of each possiblity.

And freewill, if you're into that sort of thing.

[Neosutra]

So if a single theory of everything was discovered from which all forces of the universe could be derived, including gravity, would we be able to predict the future? Or would probability clouds fix that?

Sure, we could predict all possible futures, if you woudlnt mind entering in the infinite number of quantum variables into a computer capable of running infinite permutations of each possiblity.

And freewill, if you're into that sort of thing.

Yes... that would be listed under "infinite permutations of each possiblity".

[Obev]

In the ever-apt words of Bill Hicks, if these aliens are powerful enough to traverse the known universe, why do they always end up in places like Butte, Montana?

I've always felt that the problems in interstellar flight do not stem from the excess speeds required to make any sort of journey across the stars, but from acceleration. Once you're at 90% of the speed of light, all is good, but the question is how do you get to there from a standing start? A constant 1G acceleration sounds awesome in principle, providing enough acceleration to hit near-light speed and with the added bonus of artificial gravity, but in reality the amount of fuel required to maintain such a speed is frankly colossal. Alastair Reynolds solved it in his fiction by cheating, essentially saying "uh... black holes, but backwards! Infinite energy yeah. Shut up. Oh look, an exploding star!" Beyond that, I really can't see a way to propel a potentially massive vessel through the cosmos at a constant rate for decades of time, whichever point of reference you're looking at it from. 'Course, once we do find out how to make interstellar journeys possible, I'm signing up for the first mission to mutilate alien cattle and make their rednecks scared.

[Khamsin]

It's been a while since I've studied this sort of thing, since in the field of civil engineering, we prefer things not to move. Perhaps someone can refresh my memory, since I do know that it takes an exponentially increasing amount of energy to continue to accelerate a mass through space, I just forget why.

Now, a mass moving through a frictionless medium with a constant speed (no acceleration) requires no external force to continue moving, correct? A frame of reference that moves at a constant speed is indistinguishable from a frame of reference that is standing sill, correct? Only acceleration is "felt", and requires a force.

Now, there is a certain amount of energy required to accelerate a mass at a certain rate. If you apply a force for a time interval T, you've expended E energy and the mass has increased in speed from V0 to V1. Why is the energy required to take the mass from V1 to V2 more than the energy required to take the mass from V0 to V1? Is this only something that pops up at relativistic speeds?

If we look at it in terms of (1/2)mv^2, the velocity (even if constant) is obviously a big factor in the mass's kinetic energy, although is just a property of that mass and is not the energy required to expend. However, in this case, in what frame of reference is the kinetic energy calculated from? That is, the velocity is with respect to something. In space, there is no fixed point by which to reference other objects. How does one determine the velocity of an object or it's kinetic energy? Are we already moving at the speed of light, with respect to light?

[Neosutra]

Civil engineers do math?

(j/k)

[Luto]

You can't have free will and predetermined events. It's one or the other.

[Khamsin]

Civil engineers do math?

(j/k)

Surprisingly little, actually, lol. Except for my professional license exam. There's a lot of formulas (mostly empirical, some physics based) that I had to study and know for calculations on the exam, but on the job we rely mostly on tables and standards which are themselves based on years of empirical data. Although it is important to at least understand the physics behind what we're doing so we can exercise common sense in looking at a design and imagining if it's going to fail under expected loads, but for the most part it's not very math intensive. Integrals, finding points on a parabola, and conservation of energy are about as complicated as we get.

[Kaylia]

With Newton physics
F=m*a
A constant force will always result in a constant acceleration. It's just like you said.

In relativity, energy needed to accelerate something is proportional to to lorentz factor. Because of this, it will tend toward infinite as you get close (0.9c + is usually where we start considering the effect)

That is, the velocity is with respect to something. In space, there is no fixed point by which to reference other objects. How does one determine the velocity of an object or it's kinetic energy? Are we already moving at the speed of light, with respect to light?

Inside a ship that moves at 299 999km/s, Newton's mechanics would apply the same way they are applied on Earth. Light inside the ship would move at 300 000km/s, and the ball you tossed at 10km/s is going to act like you would expect it to on Earth.

[Woozie]

Now, there is a certain amount of energy required to accelerate a mass at a certain rate. If you apply a force for a time interval T, you've expended E energy and the mass has increased in speed from V0 to V1. Why is the energy required to take the mass from V1 to V2 more than the energy required to take the mass from V0 to V1? Is this only something that pops up at relativistic speeds?

The answer to that question is "Yes".

At relativistic speeds, you have to take into account momentum dilation (or "mass" dilation).

P=mv/sqrt(1-v^2/c^2).

So getting an object from 5 metes per second to 10 meters per second requires less energy than getting it from 2947000000 to 2947000005 meters per second.

The formula for kinetic energy is no longer (1/2)mv^2. It's http://upload.wikimedia.org/math/a/2...2f15d7578d.png

where M is the rest mass times 1/sqrt(1-v^2/c^2)

[Luto]

Woozie will you please put your math shit to use and make an amazing device for time travel or the device from Sliders? And then I can test it. I'll let you come along I suppose.

[Kaylia]

Woozie will you please put your math shit to use and make an amazing device for time travel or the device from Sliders? And then I can test it. I'll let you come along I suppose.

I tried, but when I had to place that screw at sqrt(-1) inch of the infinite energy condensator, I had to give up.

[Khamsin]

In relativity, energy needed to accelerate something is proportional to to lorentz factor. Because of this, it will tend toward infinite as you get close (0.9c + is usually where we start considering the effect)

...

Inside a ship that moves at 299 999km/s, Newton's mechanics would apply the same way they are applied on Earth. Light inside the ship would move at 300 000km/s, and the ball you tossed at 10km/s is going to act like you would expect it to on Earth.

But what is the ship moving at 299 999km/s with respect to? Whoever is observing it? So that would mean that not only is mass, length, and time relative to the frame of reference, but energy too? i.e. the observer who sees you moving at 299 999km/s calculates that you need E energy to make it go faster, whereas the observer following you at 150 000km/s calculates that you only need E energy to go faster, and the observer following you at 299 998km/s calculates that you only need E energy to go faster? But when the mass and desired velocity increase is adjusted for all frames of reference (e.g. 1 kg @ 1 km/s faster to me is 100000kg @ 0.00001 km/s faster to the observer seeing me travel at 299 999km/s), the energy then comes out to be the same in all cases?

[Woozie]

The energy expended is going to be expended while you're accelerating. Regardless of the speed of the observers, any observer in any inertial frame will see you accelerate the same amount, and hence will all get the same value for the change in energy.

So in your example, the observers in every frame will see the same acceleration (and the same change in energy) even though they were all moving at different velocities (as long as they're all in an inertial frame).

[Takiwaki]

You can't have free will and predetermined events. It's one or the other.

Why? how does one pertain to the other?

free will = choice
predetermined = already set choice
if you want to talk about absolute free will with control over all events then you are talking god like power.

you can have free will and predetermination co-existing. its the same with desitiny. has it already been set? maybe, but according to our limited perception, since we cannot see past a certain point in time our choices made are free to us. infinite paths to one outcome. you can chose which ever path you want = free will. but the outcome is what we cannot chose, because we are limited 4th dimensional creatures we dont know that.

or

free to chose within a limited boundary. e.g multiple choice questions. the answers are predetermined either A B C or D

but.. you have free will to chose between the predetermined.

[Khamsin]

The energy expended is going to be expended while you're accelerating. Regardless of the speed of the observers, any observer in any inertial frame will see you accelerate the same amount, and hence will all get the same value for the change in energy.

So in your example, the observers in every frame will see the same acceleration (and the same change in energy) even though they were all moving at different velocities (as long as they're all in an inertial frame).

How can the acceleration and energy expenditure measured be the same from all frames of reference?

If I'm on a ship moving at 299 999km/s, and I throw a baseball at 1km/s, the observer who sees me going that fast will not see the ball at 300 000km/s, they'll only see it going at 299 999.00001 km/s.

Or is this a technicality, in that the acceleration really is the same, but the observed duration that this acceleration takes place is different? e.g. from my view within the spaceship, an object accelerates at 1km/s^2 for 1 second, increasing the velocity by 1 km/s. But from outside the ship, they still observe a 1km/s^2 acceleration, but only for 0.00001 seconds?