21 replies to this topic

[CodeCat]

After playing Portal, I was thinking a bit about how the portals work. And then I realised that they could never actually exist for real because they violate very fundamental laws of physics.

First of all, the law of conservation of momentum. Portals do in fact conserve the velocity of objects, and therefore also the total amount of momentum (because mass does not change). However, what they do not conserve is the direction of momentum. In fact, when you'd fall into a portal on the floor and come out of one that's also on the floor, first of all your downward momentum would disappear, and then it would reappear directed upwards. This is a clear violation of the law, because it results in a total addition of twice your original momentum: one to nullify your existing momentum and a second time to create the same momentum again facing the other way.

A second law that's violated is the law of conservation of energy. In a gravitational field of a certain strength, your energy of momement is determined by two things: velocity in the form of kinetic energy (E=1/2*mv^2), and height in the form of potential energy (E=mgh). The total energy you have is the sum of those two. Normally, when you fall, your kinetic energy starts at zero since you're not moving at the beginning, but as you fall your potential energy drops (since your height decreases) but it gets turned into kinetic energy because you start falling faster and faster. One kind of energy is turned into another kind, but the total amount stays the same. If there were portals on the floor and ceiling, whenever you fell into the floor portal at a certain velocity, you would keep the kinetic energy you had but would immediately gain more potential energy when you appeared at the ceiling. This potential energy would then be turned into kinetic energy when you fell, and you would again gain more potential energy when you fell through the portal, and the cycle would repeat itself. Effectively this would allow you to gain an infinite amount of kinetic energy over time out of nowhere, which clearly violates the law.

A funny consequence of the Portals if they WERE real is that it would be possible to move the earth out of orbit using just a single person. Objects with mass attract each other, and while the movement from the earth attracting a person is severely greater than the movement of the earth from the person attracting it, the earth does in fact move a tiny bit towards the things that fall towards it. However this normally stops as soon as an object hits the surface of the earth because it can't fall anymore. Its potential energy has now dropped to zero. With portals, you could effectively keep on falling, and all the while keep attracting the earth towards you without actually ever hitting it. Over time, this would eventually lead to enough acceleration to the earth to dislodge it from its orbit and send it flying into space.

Another interesting use of portals would be particle acceleration, for the very same reason. Because gravity through the portals would eventually accelerate anything to an infinite speed, a pair of portals with particles falling through them would make the ideal particle accelerators. Just place them between the portals and wait. Eventually the particles will be falling at near-light speeds if you wait long enough.

[Wizard]

Surely if Portals were to exist then they would be the exception to the laws, or rewrite them. You make a very sound argument, but ultimately you must concede that the laws of physics are based soley on the knowledge available to us now. What if portals already exist but we have not been able to discover or manipulate them as yet. Would this discovery destroy the very foundation of physics? Would their discovery mean that I attract the earth to me and not as we believe now?

Interesting topic!

[Waris]

Wizard, on 14 Dec 2007, 21:47, said:

Would their discovery mean that I attract the earth to me and not as we believe now?

A body is no different from the other and while a force attract you to a body then surely your body will exert the same amount of force, in the opposite direction, to 'attract' the body.

[CodeCat]

Indeed. You do in fact attract the earth, that's a fact. The third law of newton (in reality just the law of conservation of momentum) states that that if one body exerts a force on another, an equal and opposite force is exerted on the first. It's this law that explains why weapons have a 'kickback' when fired. The force pushing the bullet out of the gun also pushes the gun back with the same force. Essentially, it's not the gun pushing the bullet out, but the explosion of the gunpowder pushing the two apart.

[Reaper94]

DUUUUUUUUUUUDE.... did u take A*******************************************************************************
*********************************************
Physics in your equivelent of engalnds "GSCE's"?

[CodeCat]

I did a year of physics in university, then I got bored and switched to computer science.

[Dauth]

Its very much correct from the quick skim i made, thanks for this topic as it will aid me, it debunks rubbish science.

[ChesterM]

If you had a portal on the floor and on the ceiling, you would soon have a wind tunnel. (And you are totally right about it moving earth, I had this exact realization while reading the second paragraph of your post)

I can't quite agree with your second point of us never being able to bend/loop/break space just because it might result in "free" energy due to gravity. It would certainly break our current knowledge of physics, but doesn't mean it can't happen, or that it would have the effect we assume. We would simply have to begin trying to figure out what that would mean for our idea of the nature of things. Science has a tendency to have to do this a lot.

[Cryptkeeper]

theres one problem physics in its self is being rewritten as we speak

wormholes basically equal portals but yes they break the laws of physics becuase they create there own disruption of normal space so they can't even be applied to common physics so basically they create there own space but can this even be done but thats were scifi and theoretically science come in

Edited by cryptkeeper, 18 December 2007 - 01:57.

[Foxhound]

Chester's right. We change long thought of theories a lot (Earth being the center of the universe, creationism vs. evolution, Pluto's planethood, etc.)

[CodeCat]

Maybe so, but even basic theories like conservation of momentum and energy still hold under extreme theories like quantum mechanics. A theory as pervasive and fundamental as those are would probably not be broken.

[Foxhound]

You must also remember that the way science is taught in this day and age is that nothing is absolutely certain and that there is no true limit to anything.

Quantum mechanics could make some of these things possible, however.

[Dauth]

Watch what you say about quantum mechanics, not even the best physicists of the last 100 years are fully sure what it means.

I think it is safe to say that no one understands quantum mechanics.
Richard Feynman

Anyone who is not shocked by quantum theory has not understood a single word.
Niels Bohr

And an unattributed quote

* Quantum mechanics: the dreams that stuff is made of.


Feynman got the Nobel prize for Quantum Electro Dynamics
Bohr for contribution to Quantum mechanics

Feynman also famously said, 'shut up and calculate' because trying to explain it is so hard.

Quantum mechanics still obeys the conservation laws of Energy and momentum, albeit with the caveat of the uncertaintly principle, however trying to get more than a blackholes worth of energy at one point in time, and thus breaking the spacetime metric is so unbelivably unlikely, let alone short lived that it is a flawed concept.

[Mathias]

Its fun how we struggle to grapple with such concepts because our minds are so tailored to the specific abstractions of the world we experience from day to day.

[Dauth]

Humans live in 3 spatial dimensions and 1 temperal dimension.

Trying to do physics in 4d spacetime is bloody hard, so thinking of particles as a probability function is quite a task indeed.

[CodeCat]

I don't really have any trouble with spacetime. It's just another dimension.

But anyway, the trouble is not so much that theories can be changed, but the problem of explaining all the existing occurrences where the theory DID work. In the case of conservation laws that means you'd suddenly lose the ability to explain the whole universe once the theory is adapted.

[ChesterM]

Heh, looks like my comment caused a ruckus.

The portals have some things which we would need clarification on, such as how gravity would react with them (Would the top one pull you up? You could very well get some weird gravity going on there)

Basically we have no idea HOW the portals do what they do, we don't know how it is achieved, what amount of energy is need to maintain whatever is happening, how that energy is used etc. Basically we are making assumptions on something, when we don't even know the basis of how it works. Think of pilgrims showing Indians their boomsticks. It was unexplainable magic. Then they realized no wait, it was pretty simple when someone showed them.

It could also very well be the portals themselves that accelerate the object up or down. They already change what the orientation of a person is.

I also mentioned the laws of physics not exactly applying, because we don't actually know how things would work out when messing around with weird dimensional stuff. We could very well discover laws under our current laws which would explain things even better, or at least will eventually.

Edited by ChesterM, 19 December 2007 - 01:15.

[Dauth]

One of the Postulates of Special Relativity: The laws of Physics apply in any inertial frame.
(Ie assuming same conditions outside, you'll get the same results)

If you break this then you lose electromagnetism, general relativity and more theories.

Its not happening, Portals are Fiction, the World is Fact, Deal with it.

[CodeCat]

Actually what you say isn't entirely true. The laws of general relativity apply regardless.

What happens is that in the limit when gravity is zero and movement is zero, the law of general relativity limits to the classical laws of Newton. Adding a gravitational field or making things move around distorts those classical laws by a small amount, but this distortion is accounted for in general relativity. The effects of the distortion only become noticeable once the circumstances become more extreme. Like near strong gravitational fields or at very high speeds. But in each case, general relativity can account for the effects, so it still applies.

The only time where general relativity does not seem to apply completely is at very small scales where quantum mechanical effects are dominant. The theory seems to break down and lose its validity at this small level. Unifying general relativity with quantum mechanics is one of the great problems that still needs to be solved.

[Strategia]

All this is assuming portals work exactly according to our understanding of the laws of physics, and do not require additional laws we have not discovered/theorised about yet since we have had no occasion to do so. Also, CodeCat, your statement works on the assumption that a portal is something which just repositions an object. For all we know, portals are portals more in the fantasy sense than the scifi wormhole sense, in that they are portals to different quantum universes. According to some theories, there exists a universe for every single possibility of EVERYTHING, which means that there are a LOT which differ in literally microscopic level, say, a molecule of air moving in this direction instead of the other. Therefore, those universes are, for all intents and purposes, exactly the same as many others, and portals might link these universes. An object falling through a portal does come out the other end, but in a different quantum universe. And because of the nature of these portals, it emerges into another universe where what happened with the portals is exactly the same as the originating universe. Ergo, the turret falling up and down into the different portals in the demo video is not the same turret, it is an entirely new turret for every time it touches the surface of the portal.

At least, according to my Wild Theory™.

[Dauth]

And as soon as someone comes up with a mathematically viable, and physically reasonable theory that stand sup to scrutinity, we'll pay some attention.

It's completely unprovable, same as most religions, and therefore another blind alley for stupid science.

Any new laws must obey the old laws too, otherwise physics breaks, and then you have a real issue explaining how nuclear reactors work.

[ChesterM]

ITT: People getting worked up about imagination.