112 réponses à ce sujet

[Amatoxin]

Captain Cornhole wrote...
You sir are brilliant.

Thanks.

[Amatoxin]

If the universe was truly infinite, everything that could possibly happen would have happened somewhere. But it's not infinite, so that's not worth worrying about - it's definitely finite in size. I don't personally agree with the many-worlds view on quantum mechanics (which is where the infinite universes thing comes from) but if that's the case, there is a new universe for every single possible outcome of every random event that happens. So, if you roll a 20-sided dice, there are 20 new universes created (well as a dice roll isn't really random, it wouldn't, but you get the point hopefully).

[TheMufflon]

The whole "a new cosmos is created for every choice we make" theory is really just a misinterpretation/oversimplification of the Many Worlds Interpretation (MWI) of quantum mechanics.

[Amatoxin]

Yeah, that's what I'm trying to say. But it's a good approximation for the idea behind the MWI.



As I've said, I don't put much stock in the MWI at all.

[Kekse2k]

I've always found thinking about the many-worlds theory is fun. I may be wrong in my interpretation of it (I anticipate it, actually), but *if* it were true, then there are random people in other universes possibly spontaneously combusting due to some freak collision and that I was lucky enough to be in a world where these freak accidents don't occur, whereas other universes have people who have grown accustomed to these freak accidents, and others are just like ours waiting to be surprised by a freak accident. No wonder this is used to explain things in fictional works...it's fascinating!

[Pacifien]

Possibly because it relates to Mass Effect ever so minutely, I decided to concentrate on learning what I could about dark matter and dark energy. It's been a slow process because the last time I delved into physics was in high school. So I decided to compile what I've been able to figure out and see what else I could be taught on the matter.

Dark Matter
So scientists were attempting to research, predict, and explain the motion of a galaxy in relation to itself and those in its immediate vicinity. It's like someone looking upon a whirlpool and trying to figure out why it is spinning. Only scientists discovered that the motion of the galaxy defied their expectations and equations based on what matter we could detect. To explain this conundrum, they determined there had to be an additional element, an element undetectable aside from its affect on other matter through gravitional forces. This is what became known as dark matter. As far as I can tell.

Dark Energy
Now looking at galaxies on a much larger scale, clusters of galaxies. It's starts with Hubble's Law which states that space is expanding at a constant rate in all directions, the further away objects are from each other, the faster they're moving apart from each other. The actual observation implies this isn't actually the case. Objects we see further back in time appear to be moving at a slower rate in relation to each other versus the objects we see more forward in time. This is where I began to be completely flummoxed.

We can observe Type Ia supernovae, which are a type of supernova that is known to occur at a certain mass, and how because we know the mass, we know how bright it will be. And because we know the brightness in absolute terms, we can calculate how far the supernovae are by looking at how bright they are. If we know one supernova is a certain level of brightness and another supernova is 1/4 of the brightness, we know it's twice as far away.

However, if we measure the redshift of the galaxy where we find that supernova, it would indicate that the galaxy should be moving at a faster speed than the actual distance of the supernova suggests given a constant rate of expansion of the universe. So the question is why is the object moving faster than expected, which is where we get the idea of dark energy.

My Brain Hurts
So there's a mathematical model of how the nature of the universe should work in its large scale. But our actual observations of the universe don't fit neatly into the mathematical model. The unseen forces of dark matter and dark energy are throwing the calculations off. Which could be viewed like the theory of epicycles to explain planetary motion, when it became apparent that having planets move in a perfect circle around the Sun created various issues from the actual observations. In order to make the theory stick, they keep creating epicycles upon epicycles to explain these variations until Kepler suggests the completely mind-blowing theory of the ellipse. Dark matter and dark energy are the epicycles. Or maybe they're not. They could be aether. Or maybe not.

[Amatoxin]

The epicycles aren't really a good comparison. They were a result of the "science" of the time dogmatically sticking with the Church's earth-centred universal view. It wasn't circular orbits that caused the problem of epicycles, it was the utterly baseless assumption that the Earth was the centre of everything.



Dark energy is really just a "there's something causing the universe to accelerate in its expansion and we don't know what it is", not really a theory in itself. Science of today is willing to admit there are some things we just don't know, and generally any new explanation for exactly what causes the effects of dark energy and dark matter is looked into quite thoroughly.

[Pacifien]

StarWrecker wrote...
The epicycles aren't really a good comparison. They were a result of the "science" of the time dogmatically sticking with the Church's earth-centred universal view. It wasn't circular orbits that caused the problem of epicycles, it was the utterly baseless assumption that the Earth was the centre of everything.

Not really. Copernicus used epicycles and his theory was heliocentric.

[Pacifien]

StarWrecker wrote...
Dark energy is really just a "there's something causing the universe to accelerate in its expansion and we don't know what it is", not really a theory in itself.

I'm pretty sure it's a theory when scientists say 70% of the universe consists of it.

[Amatoxin]

Truth - I forgot about the details of Copernican theory. But then again, he used epicycles most likely becuase he was so used to them in the geocentric theories. That said, all it took was for Kepler to generalise his result further - which happens all the time in science. Someone makes a model, and someone else improves it.



It's called dark for a reason. We know that 5% of the universe's energy density is what we can see. We know that another 25% is some hitherto unknown but measurable gravitational force (ie dark matter). And the remaining 70% is... whatever's causing the rest of what we're not seeing, which has the net effect of making the universe expand faster.



It isn't really a theory if it's dealing in "I don't know".

[Pacifien]

StarWrecker wrote...
Truth - I forgot about the details of Copernican theory. But then again, he used epicycles most likely becuase he was so used to them in the geocentric theories. That said, all it took was for Kepler to generalise his result further - which happens all the time in science. Someone makes a model, and someone else improves it.

Kepler didn't improve upon Copernicus's theory. He tried to calculate the orbit of Mars from Tycho Brahe's observations and discovered it worked with an ellipse.

It's called dark for a reason.

Because it has a nice symmetry with the term "dark matter?"

It isn't really a theory if it's dealing in "I don't know".

Okay, a hypothesis.

Modifié par Pacifien, 03 avril 2010 - 07:13 .

[Amatoxin]

Kepler wrote his laws long after Copernicus' death. Copernicus had already established the heliocentric idea at that point - his major contribution wasn't the circular orbits, it was moving away from geocentricism. "We can only see so far because we stand on the shoulders of giants".

[Amatoxin]

And I'm going to duck out of this thread for a while; I'm starting to get too tired to make coherent posts, so I might go and play some Dragon Age and then sleep. I'll be back on this thread tomorrow though.

[Amatoxin]

Eli-da-Mage wrote...

It'd be funny as hell if space actually did have an end but it looked exactly the same as the rest of space. Some guy just crashes into it.

Reminds me of smacking into a map boundary on a game.

[Sloth Of Doom]

Eli-da-Mage wrote...

Oblivion Elder Scrolls has the weakest map boundary excuse ever:
"You cannot go that way, turn back"

That is what it says when you reach the edge of the universe.  It is a real pain when the edge isn't straight or defined and you keep seeing it over and over when all you want to do is go back.

[AngryFrozenWater]

StarWrecker wrote...

Eli-da-Mage wrote...

It'd be funny as hell if space actually did have an end but it looked exactly the same as the rest of space. Some guy just crashes into it.

Reminds me of smacking into a map boundary on a game.

This is what Max Tegmark said about that:

If anything, the Level I multiverse sounds trivially obvious. How could space not be infinite? Is there a sign somewhere saying “Space Ends Here—Mind the Gap”? If so, what lies beyond it? In fact, Einstein’s theory of gravity calls this intuition into question. Space could be finite if it has a convex curvature or an unusual topology (that is, interconnectedness). A spherical, doughnut-shaped or pretzel-shaped universe would have a limited volume and no edges. The cosmic microwave background radiation allows sensitive tests of such scenarios [see “Is Space Finite?” by Jean-Pierre Luminet, Glenn D. Starkman and Jeffrey R. Weeks; Scientific American, April 1999]. So far, however, the evidence is against them. Infinite models fit the data, and strong limits have been placed on the alternatives.

Source: Parallel Universes (page 42).

[AngryFrozenWater]

To the OP: About your original topic... Here is a video in which cosmologist Max Tegmark explains the concept of space-time.

Edit 1: You can find more videos like this on his homepage.

Edit 2: It looks like these videos are intended to be watched in sequence. Start at the top one.

Modifié par AngryFrozenWater, 03 avril 2010 - 04:28 .

[GreedIsNoException]

Anti Matter

In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles. For example, an antielectron (a positron, an electron with a positive charge) and an antiproton (a proton with a negative charge) could form an antihydrogen atom in the same way that an electron and a proton form a normal matter hydrogen atom. Furthermore, mixing matter and antimatter would lead to the annihilation of both in the same way that mixing antiparticles and particles does, thus giving rise to high-energy photons (gamma rays) or other particle–antiparticle pairs.



My favorite. Anti Matter

[Vormalon]

Hey StarWrecker, thanks for all your input its really educational. Sorry to go back in the discussion but could you explain what happens to Gamma at 100% the speed of light. Because the diagram makes it look like its infinite, but wouldnt that mean that light is always infinately ahead of us? Its confusing.

[Amatoxin]

Vormalon wrote...

Hey StarWrecker, thanks for all your input its really educational. Sorry to go back in the discussion but could you explain what happens to Gamma at 100% the speed of light. Because the diagram makes it look like its infinite, but wouldnt that mean that light is always infinately ahead of us? Its confusing.

Gamma is infinite at 100% of the speed of light. If you look at the equation, when v = c, it goes to 1/0.

This means that light is special. And all of this theory comes from the fact that light is special. Its velocity is always the speed of light, from every observer's point of view. Which is very, very hard for anyone to grasp.

The short answer is that gamma doesn't really apply to light. Light doesn't (well it does if you want to be a pedant, but that's way out of the scope of what I'm saying here) have mass, so it's not really bound by those restrictions. Since your mass is equal to gamma times your rest mass, as you approach the speed of light, your mass approaches infinity - meaning it is impossible for anything except light to have that speed.

[GreedIsNoException]

Particle accelarator



A particle accelerator[1] is a device that uses electric fields to propel ions or charged subatomic particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: linear accelerators and circular accelerators.



In the early 20th century, cyclotrons were commonly referred to as atom smashers.[2] Despite the fact that modern colliders actually propel subatomic particles—atoms themselves now being relatively simple to disassemble without an accelerator—the term persists in popular usage when referring to particle accelerators in general.[3][4][5]



In the future, the possibility of black hole production at the highest energy accelerators may arise if certain predictions of superstring theory are accurate.[18][19] This and other exotic possibilities have led to public safety concerns that have been widely reported in connection with the LHC, which began operation in 2008. The various possible dangerous scenarios have been assessed as presenting "no conceivable danger" in the latest risk assessment produced by the LHC Safety Assessment Group.[20] If they are produced, it is proposed that black holes would evaporate extremely quickly via the unconfirmed theory of Bekenstein-Hawking radiation. If colliders can produce black holes, cosmic rays (and particularly ultra-high-energy cosmic rays, UHECRs) must have been producing them for eons, but they have yet to harm us.[21] It has been argued that to conserve energy and momentum, any black holes created in a collision between an UHECR and local matter would necessarily be produced moving at relativistic speed with respect to the Earth, and should escape into space, as their accretion and growth rate should be very slow, while black holes produced in colliders (with components of equal mass) would have some chance of having a velocity less than Earth escape velocity, 11.2 km per sec, and would be liable to capture and subsequent growth. Yet even on such scenarios the collisions of UHECRs with white dwarfs and neutron stars would lead to their rapid destruction, but these bodies are observed to be common astronomical objects. Thus if stable micro black holes should be produced, they must grow far too slowly to cause any noticeable macroscopic effects within the natural lifetime of the solar system.[22]