74 réponses à ce sujet

[piemanz]

5* thread,thanks for the info!

[abstractwhiz]

Wormholes that connect widely separated areas of the universe are completely possible from a theoretical standpoint, in that they are permitted by one possible solution to the Einstein field equations (the 'meat' of general relativity, pretty much). They're usually called Einstein-Rosen bridges or Schwarschild wormholes. If you watched Sliders, one of their epic fails was to call their portals Einstein-Podolsky-Rosen bridges, presumably because some idiot writer read about the EPR paradox and got confused. <_<

Kip Thorne is also famous for postulating a method by which an advanced civilization might make wormhole travel possible. Your normal Einstein-Rosen bridge is unstable, and you can't even get a photon through without destabilizing it. Thorne came up with the idea of holding them open using exotic matter. This is a weird sort of thing with negative mass, but it too is theoretically possible. In Carl Sagan's fantastic book Contact (not the crappy movie, which is a travesty <_<), the group traveling through the wormholes includes two physicists, who are totally having mindgasms analyzing what they're seeing. They suspect that they're probably traveling through Einstein-Rosen bridges held open by exotic matter. 

This book almost certainly inspired Mass Effect to some extent. Observe the similarities - the civilizations who regularly use the wormhole system didn't build them, and don't know how to. They just found them, and know how to use them, but they've never found the builders. To top it off, there are signs of a galaxy-wide civilization existing at some point in the past, but they mysteriously vanished billions of years ago. It's the same in every other galaxy too. Someone built an intergalactic subway system, and then packed up and left, probably in the middle of lunchtime...

[Dethateer]

Ack, Sliders. The horror...

So there's more to Contact than that semi-time freezing wormhole (I thought it all happened telepathically, but that doesn't explain the 8 hours of static) thing and aliens who take human form?

[SuperMedbh]

AngryFrozenWater wrote...
 According to Thorn it's center (the singularity) warps spacetime into time and that causes that anything inside its horizon cannot escape and will be sucked into the singularity. Because of its spin the spacetime around that black hole warps violently and is responsible for a quasar that spits out giant beams of energy.

When Kerr did the math, he discovered that when angular momentum was imparted to a singularity, it could be solved with non-zero radii.  In other words, a ring shaped singularity.  Thus, the space-time curve of an object passing the event horizon does not have to terminate in the singularity, but can go elsewhere--  even elsewhen.

Fun, science fictional stuff, but Penrose in 1968 found that the interior solution is unstable.  Introduce an outside force (like our would be starship), and it collapses.  Besides, as Thorn points out, even were there a stable Kerr black hole, the tidal forces would rip our spaceship apart.

The quasar as a white hole hypothesis was around for a while, but these days they're thought to be the observed energy caused by accretion of matter at the centre of very young galaxies into supermassive blackholes.   Which is still fairly "wow", just not a particularly useful way of getting to Ilos

[SuperMedbh]

abstractwhiz wrote...

This book almost certainly inspired Mass Effect to some extent. Observe the similarities - the civilizations who regularly use the wormhole system didn't build them, and don't know how to. They just found them, and know how to use them, but they've never found the builders. To top it off, there are signs of a galaxy-wide civilization existing at some point in the past, but they mysteriously vanished billions of years ago. It's the same in every other galaxy too. Someone built an intergalactic subway system, and then packed up and left, probably in the middle of lunchtime...

Heck, look at the machine in Contact:


See any similarities?
http://c.imagehost.o...0/MassRelay.png

[michaelj]

Walrusninja wrote...

... Honestly I find ME more believable than politics. Respect for the great post.

BWHAHAHA! Side you in this one.

But you realize that even Alice in Wonderland is more believable than politics, do you?

[AsheraII]

Just saying for those loving to throw in the E=MC^2 theory: it's probably a correct theory. But it's also highly probable that it is an incomplete version of a much longer equation.

[abstractwhiz]

Dethateer wrote...

Ack, Sliders. The horror...
So there's more to Contact than that semi-time freezing wormhole (I thought it all happened telepathically, but that doesn't explain the 8 hours of static) thing and aliens who take human form?

Yeah, tons more. The book is one of my all-time favorites, and I was pretty happy when I heard they made a movie out of it. Unfortunately they ignored all the stuff that made the book fun, so when I finally watched the movie, I started out as , and slowly went to  to  to <_<.

[abstractwhiz]

AsheraII wrote...

Just saying for those loving to throw in the E=MC^2 theory: it's probably a correct theory. But it's also highly probable that it is an incomplete version of a much longer equation.

Er, E = mc^2 is just the popular version, and it's only true in frames of reference where the object under consideration has zero momentum. A more accurate and general formulation is E^2 = m^2 c^4 + p^2 c^2. The p term here represents momentum, and setting it to zero gives the famous version. 

But yes, the spirit of what you said is pretty much on the money. 

Modifié par abstractwhiz, 16 avril 2010 - 05:46 .

[Dethateer]

Why is momentum multiplied by the speed of light? Not saying it's wrong or anything, just trying to understand.

Modifié par Dethateer, 16 avril 2010 - 05:48 .

[abstractwhiz]

Dethateer wrote...

Why is momentum multiplied by the speed of light?

Because the equations come out that way, that's why. 

I can do a vague sort of explanation, but the answer is really in the mathematics. Words are a poor way to describe the universe. 

Suppose you're sitting in a car driving along at 50 kph, and then you throw a stone at a Krogan (you like to live dangerously) standing on the road. Now from your perspective, you threw the stone at a paltry 5 kph, but our poor friend on the road was just brained by a rock traveling at 55 kph, because the car was moving with respect to him. Now you can analyze this system in two ways. You can do it in the road frame, in which case the victim is stationary, the car moves at 50 kph, and the stone moves at 55 kph. Or you can look at it from the car frame, in which case the car is stationary, the stone travels at 5 kph, and the guy on the road is moving towards you at 50 kph. It's pretty easy to convert from one reference frame to another - it's pretty intuitive. The equations used for this are usually called the Galilean transformations. Pretty simple stuff.

Unfortunately, human intuition doesn't always work. Now let's imagine you're in a spaceship traveling at 0.5c (half of lightspeed), and you shoot a laser at the long-suffering person on the street. From your perspective, the laser moves at c (lightspeed). The Galilean transformations would indicate that the unfortunate Krogan will be hit by a laser traveling at 1.5c. 

The weird thing is that it doesn't happen. He's hit by a laser traveling at exactly c. In fact, no matter how the source or observer is moving, the damn thing still fires at exactly lightspeed. (If I remember right, this is predicted by Maxwell's equations, and thinking about this was what led Einstein down the path that ultimately became special relativity.)

Naturally, you can't use the Galilean transformations anymore. The correct way to transform between frames of reference is using the Lorentz transformations. These have to incorporate these strange constraints, so the speed of light enters into them. If you're moving slowly compared to lightspeed, they just reduce to the Galilean transformations again.

Since special relativity deals with stuff moving at significant fractions of lightspeed, analysis of these systems brings up the Lorentz transformation all over the place. And that's why c turns up in all those equations. 

Disclamer: I'm not a physicist, just someone who used to be a physics geek. :innocent:

Modifié par abstractwhiz, 16 avril 2010 - 06:11 .

[Noble 1]

AngryFrozenWater wrote...

Noble 1 wrote...

AngryFrozenWater wrote...

Dethateer wrote...

I'm more interested as to why the black holes at the cores of these "supermassive stars" don't suck the matter of the stars into them.

How about creating a mass effect field by feeding it dark energy? According to Dr Michio Kaku (link in my post above) maybe negative energy (which dark energy may or may not be) is required to open and maintain worm holes. If you use a similar process to cancel some of the curvature near a black hole then maybe... What am I babbling about? These are super massive black holes. I think surviving those is one of the few things that smells like fantasy.

Black holes, if spinning while they are formed can form the shape of a ring.  It would be quite safe to pass through the center of this ring.  Also,  I have read that one passing through should not expect to come out the other side in the same region of space or even in the same time

Chances of that happening are slim. Kip Thorn says that the earlier idea that "the traveller" would become infinitely thin and long or that one could pass are both unlikely. Instead forces would rip the traveller appart from all sides. He says that in reality we now know that one would be stretched and squeezed from all sides in a chaotic manner and at an ever increasing rate. One would die.

Source: What do Black Holes and Dark Matter Reveal? (Kip Thorne) (Part 1 of 3).

http://mkaku.org/home/?page_id=423
The Einstein-Rosen BridgeBut this also revives an ongoing controversy surrounding black holes. The best description of a spinning black hole was given in 1963 by the New Zealand mathematician Roy Kerr, using Einstein’s equations of gravity. But there is a quirky feature to his solution. It predicts that if one fell into a black hole, one might be sucked down a tunnel (called the “Einstein-Rosen bridge”) and shot out a “white hole” in a parallel universe! Kerr showed that a spinning black hole would collapse not into a point, but to a “ring of fire.” Because the ring was spinning rapidly, centrifugal forces would keep it from collapsing. Remarkably, a space probe fired directly through the ring would not be crushed into oblivion, but might actually emerge unscratched on the other side of the Einstein-Rosen bridge, in a parallel universe. This “wormhole” may connect two parallel universes, or even distant parts of the same universe.

[Noble 1]

Dethateer wrote...

It's not possible because the mass of a substance cannot be changed.

http://physics.fulle...~jimw/nasa-pap/
Mach's principle and local Lorentz-invariance together yield the prediction of transient rest mass fluctuations in accelerated objects. These restmass fluctuations, in both principle and practice, can be quite large and, in principle at least, negative.
There you have it.  A Mass Effect not unlike Eezo's effects

[Noble 1]

the transient Machian inertial reaction effect that makes impulse engines possible may also make "stargates" and time machines based on traversable wormholes feasible [Woodward, 1997]. This is a consequence of the strong nonlinearity of the total proper matter density as it approaches zero and negative values. (Negative mass has interesting properties. See: Forward [1989] and Price [1993].) The feasibility of such schemes, however, also depends on the magnitude of the bare masses of elementary particles and the nature of the vacuum. These matters are, at the very best, conjectural. Accordingly, the schemes are a good deal more speculative than impulse engines. But they, along with impulse engines, can be explored experimentally with present technology at reasonable cost.



http://physics.fulle...~jimw/nasa-pap/

[Dethateer]

I'm going to have to read that thing a few more times again in about 8 hours, but I get the feeling you haven't read it at all, since you posted the opening quote. Which isn't to say that the paper itself won't change my mind.

[Noble 1]

Also, If anyone is seriously interested in FTL propulsion concepts, one of the most plauusible (At least to me) is the Slipstring Drive

http://www.slipstring.com/

http://orbiter-forum...read.php?t=9530

[Dethateer]

Aren't dark matter and energy purely theoretical and unproven?
That summary reminded me of a conversation I had with a member named ModerateOsprey. Wonder if he's still around.

Modifié par Dethateer, 17 avril 2010 - 09:21 .

[Lord_Tirian]

abstractwhiz wrote...
Because the equations come out that way, that's why. 

Another way to put it is: It doesn't pop up. If you (and particle physicists do a lot), use natural units (where c = 1), it goes away everywhere and all equations still work. It's more or less an artifact of our unit systems - that we use rather arbitrary units to describe stuff, so they don't add up.

Let's illustrate it with the (incomplete) and famous E = mc^2 - the c pops up again, but let's set c = 1 and... we get E = m. Which is really the physics behind it, energy and mass are the same, just different forms of the same thing. But because we perceive it differently, we gave it totally different units (like calories and pounds or joule and kilogram), hence you need the constant © to convert it.

This is even more beautifully illustrated with 4-vectors - when you describe coordinates with not only with 3 components (x-, y-, z-axis), but include time, these 4-vectors take the form (ct, x, y, z) in the covariant formalism (or (ict, x, y, z) if you don't bother with covariance and metrics) - but if you set c = 1, the vector becomes (t, x, y, z), which is really the essence - time is "just" another coordinate - we just don't measure time and distance in the same units, due to our perception.

Modifié par Lord_Tirian, 17 avril 2010 - 11:24 .

[Noble 1]

Lord_Tirian wrote...

abstractwhiz wrote...
Because the equations come out that way, that's why. 

Another way to put it is: It doesn't pop up. If you (and particle physicists do a lot), use natural units (where c = 1), it goes away everywhere and all equations still work. It's more or less an artifact of our unit systems - that we use rather arbitrary units to describe stuff, so they don't add up.

Let's illustrate it with the (incomplete) and famous E = mc^2 - the c pops up again, but let's set c = 1 and... we get E = m. Which is really the physics behind it, energy and mass are the same, just different forms of the same thing. But because we perceive it differently, we gave it totally different units (like calories and pounds or joule and kilogram), hence you need the constant © to convert it.

This is even more beautifully illustrated with 4-vectors - when you describe coordinates with not only with 3 components (x-, y-, z-axis), but include time, these 4-vectors take the form (ct, x, y, z) in the covariant formalism (or (ict, x, y, z) if you don't bother with covariance and metrics) - but if you set c = 1, the vector becomes (t, x, y, z), which is really the essence - time is "just" another coordinate - we just don't measure time and distance in the same units, due to our perception.

Narnia fans are brilliant.  I hadn't thought of that

[Chris H. Fleming]

Dethateer wrote...

Hm, well, on the subject, what would happen if you got two black holes close together (besides absorbing each other, we're assuming that doesn't happen) and shoved a body at an equal distance from the core of each one?

2 black holes inspiral into 1 black hole while radiating away a tremendous amount of gravitational radiation. Current gravitational wave detectors are trying to detect these kinds of signals as they are fairly strong (relatively speaking). There is also a lot of computational/theoretical reasearch in determining how the signals should look.

Somebody in between could get trapped in some kind of an event horizon, but they could also get kicked out. It depends on where they are and how the black hole spins are oriented.

[Chris H. Fleming]

Dethateer wrote...

Why is momentum multiplied by the speed of light? Not saying it's wrong or anything, just trying to understand.

For massless particles (like the photon) E=pc. This formula predates relativity. It can be derived from Maxwell's equations and is also experimentally observed in experiments.

Essentially, if you shine light on a surface, the momentum imparted is proportional to the energy stored in the light.

[HughChardon]

Chris H. Fleming wrote...

 ..... For massless particles (like the photon) E=pc. This formula predates relativity. It can be derived from Maxwell's equations and is also experimentally observed in experiments.

Essentially, if you shine light on a surface, the momentum imparted is proportional to the energy stored in the light.

Yep, observable with a simple Radiometer like the one from Edmund Scientific scientificsonline.com/product.asp_Q_pn_E_3060082 

[Noble 1]

Chris H. Fleming wrote...

Dethateer wrote...

Hm, well, on the subject, what would happen if you got two black holes close together (besides absorbing each other, we're assuming that doesn't happen) and shoved a body at an equal distance from the core of each one?

2 black holes inspiral into 1 black hole while radiating away a tremendous amount of gravitational radiation. Current gravitational wave detectors are trying to detect these kinds of signals as they are fairly strong (relatively speaking). There is also a lot of computational/theoretical reasearch in determining how the signals should look.

Somebody in between could get trapped in some kind of an event horizon, but they could also get kicked out. It depends on where they are and how the black hole spins are oriented.

It's Hawking Radiation, and only small black holes do that.  The larger a black hole gets, the lower the amount of radiation

[Chris H. Fleming]

Noble 1 wrote...

Chris H. Fleming wrote...

Dethateer wrote...

Hm, well, on the subject, what would happen if you got two black holes close together (besides absorbing each other, we're assuming that doesn't happen) and shoved a body at an equal distance from the core of each one?

2 black holes inspiral into 1 black hole while radiating away a tremendous amount of gravitational radiation. Current gravitational wave detectors are trying to detect these kinds of signals as they are fairly strong (relatively speaking). There is also a lot of computational/theoretical reasearch in determining how the signals should look.

Somebody in between could get trapped in some kind of an event horizon, but they could also get kicked out. It depends on where they are and how the black hole spins are oriented.

It's Hawking Radiation, and only small black holes do that.  The larger a black hole gets, the lower the amount of radiation

No, you are confused.

http://www.black-hol...g/explore2.html