Yet every day what used to be an "absolute" in science becomes possible. An example off of the top of my head is the discovery of "metamaterials" that allow for invisibility in certain electromagnetic waves, and potentially optical light as well. Prior to this, any type of "invisibility cloak" was sheer science fiction... (Star Trek, Harry Potter, and so on)
Another was the breaking of the sound barrier. Science at the time considered it impossible. Yet, here we are today...
Breaking the sound barrier was never considered impossible by people with any knowledge in the field. Guns were firing supersonic projectiles long, long before supersonic aircraft were built. What was considered impossible was powered flight, due to the lack of powerful enough engines and propellers that would work at those airspeeds.
Going faster than light is not just a matter of making a more powerful engine. There are no known examples of FTL objects, and all data indicates that accelerating to c would require infinite energy. In addition, our measurements of fast moving clocks agree with relativity's predictions of time dilation, and FTL travel allows for paradoxes and inconsistencies. As far as we can tell, it's flat out impossible for material objects or even information to travel faster than light.
The "invisibility cloak", at least the structure you refer to, is similarly not something that was considered impossible, just impractical to design prior to the development of software to simulate the interaction of the structure with electromagnetic waves, computers to run the simulations in a reasonable timeframe, and modern manufacturing techniques to actually create the structure. And even now, it only functions as a "cloak" at one wavelength, it does not work for wavelengths even slightly above or below the designed wavelength. It'll be an incredibly useful technology in optical networking or possibly optical computing equipment once metamaterials that function at the required wavelengths can be mass produced, but it'll never be an "invisibility cloak".
The "series of cogs stepping up rotation" idea won't work for a few simple reasons. When you step up the rotation rate, you reduce the torque, mechanical power remains the same...eventually, the torque will be insufficient to overcome friction. Gear motors are easily identifiable because the output shaft is difficult to turn. Second, the gears have finite structural strength, imposing a limit on how fast they can rotate before breaking apart. Finally, given a perfectly-rigid, infinitely-strong, totally-frictionless gear train, relativistic effects will still come into play to increase the amount of work you need to do to rotate the slowest cog in the chain, such that it still requires an infinite amount of energy to accelerate the last cog to the point that its edge is traveling at c. You can't get around this with electromagnets, as electromagnetic waves travel at...the speed of light, unsurprisingly, considering that light is an electromagnetic wave. In fact, the electromagnetic interactions that hold the atoms of everyday materials together are similarly limited by c.
wcelliot: there's no contradiction within black holes. The singularity is something that is not explained by current physics and might well not exist, but the event horizon marks the point where FTL travel would be required for escape. As for tunneling or evanescent waves, such things can not carry information faster than light or move things macroscopic distances. Tunneling in particular is a quantum effect, and you have to be careful about applying the terms used to describe such effects to everyday life...they often do not mean what you'd expect, given the name of an effect. Entanglement, for instance...many people intuitively interpret it as two particles becoming tied together, so you can twist one particle to a specific state, and see that when you look at the other...however, setting one half of the pair to a known state will actually break the entanglement. You can infer the state of both halves of an entangled pair by looking at one half, but you can not set the state of the remote pair to some specific value. This makes it useful for sharing cryptographic codes, but quite useless for FTL communication.
Black hole event horizons are not material objects and do not rotate. They are portions of space where curvature of space-time equals some value. As said by mr_homm, large objects exist, fast-rotating objects exist, but no large objects rotating fast enough to have a surface velocity even approaching c exist.
excaza
17th June 2008 - 01:16 PM
QUOTE (cjameshuff+Jun 17 2008, 07:38 AM)
but it'll never be an "invisibility cloak".
You make a long post about how people say "such and such" is impossible, yet you finish it off by saying something will "never" happen?
Alcari
20th June 2008 - 02:03 AM
This system will neve form a startrek-like cloaking system, because it is specifically designed to function for a single wavelength, coming from a single direction, under a single angle. This meta-material-cilinder approach cannot be adapted for any other circumstance, look up the article (IIRC it's on 'Science')
Anyway, back on topic.
The speed of light, and why something with mass can never reach it.
General relativeity says that the relativistic momentum of a particle would increase with speed in such a way that at the speed of light an object would have infinite momentum.
To accelerate an object with mass to c would require either
- infinite time with any finite acceleration
or
- infinite acceleration for a finite amount of time.
Either way, you end up needing infinite energy. Going beyond the speed of light would require more than infinite energy, which is not generally considered to be a sensible notion.
However, something that does not have mass, such as a photon, can travel at c. After all, if something with mass 0 becomes a hundred times as heavy, it still weighs nothing.
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semi-related bonus material
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Now, for some things that'll make your wierdshit'o'meter blow:
In special relativity, it is possible for non-zero mass particles to exist that go faster then c. However, these particles cannot ever slow down, so they don't actually pass the barrier. Tachyons are the best current example, though still theoretical.
If you really want to faster then light, you have to bend the rules a bit. For instance, you can fold space, so that you are still traveling slower then light, but to an observer outside the folded area, you're going faster. You're not actually going faster then c, you just appear to be doing it.
dimazin
20th June 2008 - 03:02 AM
QUOTE (Alcari+Jun 20 2008, 02:03 AM)
The mass does not increase. Impulse does increase.
mica
20th June 2008 - 02:04 PM
QUOTE
My personal, pet theory these days is that this universe is a black hole in a higher-dimensional universe.
For wcelliott's support: My son applied the equation of the Schwarzschild radius to the total mass of the universe, put all the approximately mass in account and got the size of a black hole about r=15 Billion light years, the same size, he put in account for the calculation of the total mass of universe. Cool?!
15 Billion light years is also the distance, where the redshift ends and repulsion becomes light speed. 15 Billion years (not light years) does it approximately take, till anything (according to constance of Hubble) is unified at one point. Cool?!!
Your pet theory seems to be correct, because inside of a BH is an own space-time-system. The events horizon is it self a singularity and beyond is from our sight a big void or a space-time-bubble. Cool?!
AlphaNumeric
20th June 2008 - 03:52 PM
QUOTE (mica+Jun 20 2008, 03:04 PM)
For wcelliott's support: My son applied the equation of the Schwarzschild radius to the total mass of the universe, put all the approximately mass in account and got the size of a black hole about r=15 Billion light years, the same size, he put in account for the calculation of the total mass of universe. Cool?!
If the mass of the universe is about 10^50 then the Schwarzchild radius is 15
million light years. But since the mass of the universe isn't in a sphere of radius 15 million light years, the amount of matter in 15 million light years, compared to 15 billion, is 0.001^3 = 1 billionth.
QUOTE (mica+Jun 20 2008, 03:04 PM)
The events horizon is it self a singularity
No, it isn't.
"THEY"
20th June 2008 - 05:54 PM
QUOTE (mica+Jun 20 2008, 07:04 AM)
Your pet theory seems to be correct, because inside of a BH is an own space-time-system. The events horizon is it self a singularity and beyond is from our sight a big void or a space-time-bubble. Cool?!
I used to believe this could happen, until I studied SR a bit and gained a better understanding of it.
Alcari
20th June 2008 - 08:32 PM
QUOTE
The events horizon is it self a singularity
No, the event horizon is where no information can escape from the blackhole. To put it simply, it's where the "Black" starts.
midwestern
20th June 2008 - 08:45 PM
How can this universe be part of a black hole from a higher-dimensional universe? This is impossible, because all light would be trapped from entering the hole.
wcelliott
22nd June 2008 - 03:04 AM
QUOTE
This is impossible, because all light would be trapped from entering the hole.
No, it'd be trapped from *leaving* it.
We'd be all made up of matter that's already accelerated *beyond* the speed of light, and that square-root-of-negative-one factor implies orthogonality to the space surrounding it.
Hawking Radiation might end up being gravity - space escaping through particles with mass, particles with mass being holes in this 3D space (space being where particles can be, and particles being where space disappears).
I appreciate how this sounds more acid-trip than Quantum Mechanics, but would you really expect these sorts of issues to have mundane answers?
midwestern
22nd June 2008 - 07:43 PM
No, you would not, and I believe both entering and exiting light would not be permissive in a black hole universe.
whiterosealchemist
3rd July 2008 - 08:32 PM
i sort of understand what you are saying midwestern i was thinking about how the event horizons worked and i came to the idea that if you reached the event horizon time would stop and you wouldn't be able to move any farther as motion requires time. However then i realized that the time stop would only be to an outside observer and to the person going in time would be going on as normal. That is if you could survive the tidal forces and everything else that is highly fatal about black holes.
midwestern
3rd July 2008 - 08:35 PM
I understand whiterosealchemist. Entry into a time lapse within a black hole wouldn't allow for escaping the effects within the hole. They may even be real time.
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