Travelling at Light Speed

You're actually pretty much right on how those particles are created. Virtual particles are created in the curved spacetime around the black hole, and thanks to the high gravitational potential, they are effectivley "boosted" in energy and turn into real particles, taking away a wee bit of mass from the black hole - sort of like how the strong force binds nucleons together by increasing their mass slightly, if you see what I mean. (This is getting fairly technical, fairly fast - sorry)

But for those interested, the radiation is in the form of of a classical blackbody radiation with temperature T = (hbar)c^3 / 8piGMk. Not too sure about this, but I'm going to guess that due to the quantum mechanical nature, actual emmision is a random process.

Hmmm... this is veering off topic, but interesting isn't it how it sounds sort of like radiation from an atom. That's actually a pretty interesting idea... a black hole could be compared to a supermassive atom, radiating away energy at random, in order to return the gravitational field to its "ground" curvature...

Food for thought, anyways.

a black hole could be compared to a supermassive atom, radiating away energy at random, in order to return the gravitational field to its "ground" curvature...

Oh definitely, with the exception that an atom has distinguishable parts, and a black hole - well - does not. Otherwise, it'd seem about right. It's amazing how much matter at the large scale also seems to look like matter at the miniscule scale - although if you go indepth on either side you find there's remarkable differences. It's all part of cosmic structure. Like the spiral - it's practically the most common shape in nature. Even a circle or an orbit could be said to be a spiral (a spiral that never reaches the centre).

One question I always had was:

Why do people say time stops and all that for you if you're traveling at light speed.

Light is fast sure... but its not like traveling at light speed is all that great. It still takes light like 5 minutes or so to reach earth from the sun.

I don't understand why attributing a certain velocity means you're infinatly heavy or any of that.

Why does reaching a certain velocity mean time would suddenly stop?

Just doesn't make sense to me.

Actually, it takes 8 minutes for light to reach the Earth!

But as for mass dilation, here's a website with the mathematical principle:
hyperphysics.phy-astr.gsu.edu...
(Read "Relativistic Mass")

At this point it's too complicated to really explain. It has to do with a number of mathematical models and equations that "if this is true, then this must also be true" than stem out from special relativity.

Also, this site gives you the mathematical equaitons behind length contraction, time dialation, and the problem behind variable mass and relativistic mass, time, and momentum.

I think someone should come up with "The Layman's Explanation behind General Relativity", like what they have for the laws of thermodynamics:

0. No matter what, you have to play the game. (everything that can be observed has energy)

1. No matter what, you can't win at the game. (energy conversion can never exceed 100%)

2. You can break even, but only on a very cold day. (energy conversion can reach 100%, but only at 0K - absolute zero.

3. Unfortunately for you, it never gets that cold. (the moment you work energy through absolute zero, even to observe it, makes the energy reach above absolute zero, and so energy conversion stays below 100%)

Okay I know this is getting a bit off topic talking about black holes, but I think it's closely related with light, and space-time. Both new examples are a bit easier to understand.

My knowledge of black holes is relatively small, but I have read up a bit on them and I'm still curious. I thought black holes were always growing, but never realized that they would eventually get so dense as to be "mini big-bangs" in themselves creating matter. At what point does this happen? And if it continues to disentigrate what would happen when it reaches 0 mass?

If either of you don't mind, a post titled M-Theory for dummies would be much appreciated. I know that M-theory is the collection of super-string theories into one single theory. Is M-Theory the same thing as the unification that Einstein was working on before he died?

Well, I am unsure exactly what you mean by at what point do they become mini-big bangs? As soon as an object becomes a black hole, it starts releasing these particles. And remember, it's not "creating" mass - it's changing energy to mass. When the black hole reaches 0 mass, it seems to simply disappear - as if it winked out of existance. A black hole would not continuously grow if left without nearby matter, but would slowly shrink. Of course, if something with matter does come around the black hole, it'll consume part of it. Since there's a lot of cosmic dust and whatnot, it's unlikely that a naturally occuring black hole will fully disintigrate (at least, not until the universe is immeasurably old and all matter has already been consumed, and black holes exist universes away in distance). However, it does apply to microsingularities that we have created... thankfully.

Now, onto M-theory. When you mentioned it, I had not ever heard of it, so I decided to do some research (god how I love Wikipedia). M-theory is looking for a way to unify all the string theories that exist. String Theory itself is something that tries to tie together General Relativity and Quantum Physics.

The problems with General Relativity and Quantum Physics is that GR can explain things on the universe at the large scale, but sometimes messes up when working with the fundamental building blocks of the universe. QP, on the other hand, works perfectly well for describing what happens on the atomic level and smaller, but messes up when trying to explain things on the large scale. String Theory tries to unify these.

Problem is, there's a number of different String Theories - and some of them are right some of the time, and others are right at other times. M-Theory is trying to unify them by finding their underlying base, something called Underlying String Theory (which is then called M-Theory). M-Theory attempts to do this by finding where the mathematics, outcomes, or description of outcomes in the same - finding out where the theories agree - and then simplifying it into one theory.

So, yes, I guess you could say it's Einstein's Grand Unifying Theory - but it's extremely complicated, and requires concepts that weren't around in Einstein's time.

At the end of the Wikipedia article, it talks about Matrix Theory as currently being promising in completing M-theory - which I can only imagine works by seperating the different String Theories into a kind of descriptive or situational matrix, which could then be manipulated to find which theory would be used to which case. I do not know.

Like I said, we're getting into massively complicated and high-math subjects, which also include things which I know little or nothing about . I'm afraid that if you go much farther with questions to every post I give, that I won't be able to help!

Of course, elaborations on Black Holes I will be happy to attempt to explain.

Sorry for slightly spamming, but no one's answered yet...
If light is a constant speed for all frames of reference, does that mean that actually if you were to ever travel light speed, you'd still never catch light because it's travelling at light speed relative to you anyway?
Second thing: can mass, space and/or time dilation be explained by higher dimensions? Go back a few posts to see my full question.

Maybe my info is really out of date but i was told the reason you couldn't reach and go past the speed of light is because the nearer you get to the speed of light the more mass you have, so the more energy you need to accelerate. Once you use that extra energy to accelerate you are now going even faster than previously, so you need even more energy to accelerate. This means you need infinite energy to reachthe speed of light.

the reason light can reach the speed of light is because it has 0 mass, thus meaning it needs 0 energy for it to reach the speed of light?



[edit on 18-12-2005 by manta]

Well, yes. That's one way of explaining it empirically - the energy you put in to acclerating has to go somewhere, so it gets converted into mass. But the real issue is that the speed of light is constant for observers in ALL inertial reference frames, period - so no matter how fast you go, you'll always see light as moving at exactly c.

A photon does not have mass in the classical sense - it does have mass-energy, though. So it can actually be deflected by gravitational fields. This was shown during the 1919 eclipse in a rather beautiful proof of General Relativity - that gravitation is indistinguishable from acceleration and so can be thought of as a curvature of spacetime.

As for higher dimensions being a cause of mass? I don't think so, but there's an interesting conjecture regarding the existence of dark energy - the universe is a sheet folded many times over onto itself, and gravity leaks out in the other dimensions causing there to be more energy than we can see.

As for string theory - it's mathematicall elegant... but I don't like it at all. There's something a bit fishy about it - it feels too much like a mathematical game. And it suffers what I think is the problem with most of quantum mechanics... it relies on a background of flat spacetime... while it's a good approximation to first order, I'm willing to bet that a curved spacetime has some kind of effect. Not too sure if anyone's looked into this before, I scoured the literature breifly, but didn't see all that much. Penrose, though, has an interesting argument that claims that quantum decoherence can be explaied by general relativity - the paper itself is really confusing... I'll look into it some more and report back here if I find anything else.

If two objects are traveling near the speed of light, and their combined speed is greater than c, it doesn't matter since they are both not traveling faster than the speed of light relative to the universe.

Originally posted by Yarium
Well, I am unsure exactly what you mean by at what point do they become mini-big bangs? As soon as an object becomes a black hole, it starts releasing these particles.And remember, it's not "creating" mass - it's changing energy to mass.

Yes I know matter and energy can't be destroyed or created but only change form. I should have said converted and not created. Isn't thae big bang just a big conversion of energy to mass?

Originally posted by Yarium
When the black hole reaches 0 mass, it seems to simply disappear - as if it winked out of existance. A black hole would not continuously grow if left without nearby matter, but would slowly shrink. Of course, if something with matter does come around the black hole, it'll consume part of it.

So chances are there is very many very small black holes out there I'm guessing. What happens if two black holes were to meet? Or what is a black holes reaction to dark matter?

Originally posted by Yarium
String Theory itself is something that tries to tie together General Relativity and Quantum Physics.

Oh ok that would make it the theory of everything that Einstein was looking for.

What Happens When Black Holes Meet

Simply put, they merge into a single black holes with the combined mass of both black holes - and its direction and velocity will be a sum of their combined momentums. However, the interesting things happen at the specifics. The space-time distortion around a black hole is very wierd, and when two meet, there would be some extremely odd areas where things that would normally break physics occurs.

For example, there would be a section in between the two where you would seem to move faster than light. In truth, you are covering less space than somebody far away from the black holes, but your resultant displacements are the same. Theoretically you could also use this to travel backwards in time, by travelling faster than information.

Now, as for how the interact with Dark Matter, I think you have a misguided idea of what Dark Matter is. Don't worry, it's okay, since the term Dark Matter is tossed around so much, people tend to think it's this strange cosmic substance. Put simply, Dark Matter is normal matter that we can't see (hence why it's dark).

A planet is dark matter. We've been able to find out that there are other planets around other stars by studying a star's wobble - but there are trillions and trillions of stars that we can't study like this (they're too far away). Any planets around these stars are, as yet, undetectable. If there are planets around them, we can't see them or detect them. But their is mass unaccounted for in the universe that we see - so maybe they make up part of it.

In all truth, you are also Dark Matter to somebody in another solar system. An alien viewing the earth through a telescope might be able to determine the overall mass of the earth - but what he sees wouldn't completely fill the picture. He may see mountains and oceans and other things, which would account for most of the mass, but you might be missing from his calculations - you're a missing mass that MUST be there, but you can't see it.

But it's not just big things that are Dark Matter. More and more we're turning to the tiny. Do you know what Neutrinos are? They are subatomic particles with almost no mass. They travel at nearly the speed of light, and pass through almost all matter as if it weren't even there. Hold your hand out for 5 seconds. You done? About 3 billion neutrinos just passed through your hand. Since they have been found to have an almost non-existant mass (though they do have some mass), they've been factored into the "Missing Mass" calculation - shoved under the "catch-all" phrase "Dark Matter". Still more mass is missing.

So, what happens to Dark Matter when it encounters a black hole? The same thing as everything else - it's crunched, squeezed, super-heated, stretched, destroyed, collapsed, and other things too horrible to mention.

Oh, and as for the beginning of the universe, you're right - it was a transformation of energy to matter. The real question is, where did all that energy come from? It's an unanswerable question.

Help me understand? Time is not a constant. It has been proven that the faster something goes the slower the time for it as compared to an observer or a slower control subject. I believe it was in the sixtys that this was proven with atomic clocks and airplanes.
So, speed is measured in distance per time, but time is not a constant so how does this effect the equation for speed. It seems to me that it would be like measuring the expanding universe with a ruler that is expanding at the same rate.
Also we can slow down light propogation with thing such as bose-eistein condensates, water and glass. So canwe speed it up with a material that has a higher permiabilty to propagation?

Originally posted by TheRenegade
Sorry, I don't mean to sound like a complete idiot, but people all say that if you were to reach the speed of light, time would stop.

Who are all people? I don't say this.

I feel we Can not travel at the speed of light, Because as an object reaches the speed of light it expands indefinitely.

To Ultralo1:

The speed of light can be said to be a constant because it's "the speed of light in a vacuum" measurement that we use. If we instead chose "the speed of light in glass", everything would still work (although we'd have to factor the energy of glass into the equation for E=mc^2), since the speed of light going through glass is constant everywhere in the universe too (so long as it's the same kind of glass).

So, do you see how it can be said to be constant now? Given a distance of A to B, light will always travel said distance in the same amount of time, no matter where you are in the vacuum of the universe. If time were slowing down or speeding up, then light would seem to cross points A to B slower or faster.

Yarium, Thanks. Ithink where I am getting screwed up is in the time dialation effect. If you were traveling the speed of light your watch would still tick away at one second and it would feel like 1 second to you. The person on the ground would see one second tick off and it would feel like one second, but when the seconds were compared to each other they would be different. This is because relative to each other the one moving at a faster speed would be slower. Correct?

I too found it very difficult to comprehend this time is not a constant rule. I came across an example on "HowStuffWorks.com" which explained it inthe following example:

Imagine you have two platforms travelling at any speed parallel to each other in the same direction. If you were standing on one of these platforms and throwing a ball directly up until it hit the platform above and then caught it again once it rebounded it would take a certain amount of time to travel that distance. Let's say for arguments sake the distance from your hand to the platform above and back to your hand again was 1 metre and it took 1 second. To you the ball would be travelling at 1 metre per second. To an observing not standing on the platform, watching you travel across their field of view, the ball would also appear to be travelling at 1 meter per second. However as the ball is actually moving forward at a given speed it would not actually be travelling straight up, it would actually be travlling along a diagonal line which would be longer than 1 metre in the same amount of time. The exact distance could be calculated in accordance with Pythagoras' Theorem. Spacetime has actually been curved because depending on which way you look at it the distance travelled by the ball is greater than 1 metre in 1 second or the ball has taken less than 1 second to travel 1 metre.

This example really helped me to come to terms with this concept.