Nano

Thanks for a detailed explanation of the SN type II.

Now something "rebounds" from that huge collapse and blows off the outer layers. One possible mechanism is a wind of neutrinos. When protons swallow electrons--to become neutron matter--they BURP neutrinos. And in this collapse to neutron matter such a huge wind of neutrinos is produced that, as I recall, it is able to blow away stuff. Even though neutrinos in ordinary numbers are not very interactive and pass thru stuff without exerting any force, in very large numbers they act like a blast of wind.

The neutrinos are light, but do indeed have high velocity therefore also momentum. I can understand that their kinetic energy would blast the outer layers of, remembering that it is a vast amount of those small bastards coming from the core.

The problem, as you also pointed out, is that neutrinos hardly interact with ordinary matter, which the outer layers consist of.

In this very second 50 trillion solar neutrinos passes through your body (Wikipedia)

As far as I've understood, the whole supernova process starts with that the core is collapsing when the gravitational force is grater than the electron degeneracy pressure. This collapse happens in a very brief amount of time, and it reach to a sudden halt when the neutron-pressure and the weak force is holding back gravity for collapsing even further. Apparently it is this "halt" which is triggering the outer layers to explode. My question is how do the core and the outer layers interract? Is it particles which is carrying the kinetic energy from the core to the outer layers?

The space-time continuum is not a reference frame. You need to measure a speed in relation to a different frame, and in practical terms, something in that reference frame.

You are right offcourse. I am still in the learning process of relativity.

So a person inside a spaceship traveling close to c relative to us, would not "feel" any of the relativitsic effect? A watch carried by the captain would, in his opinion, click just normally? He would not gain any mass, or change his size?

If two spaceships leaves from earth traveling at a speed close to c but in in opposite directions relative to the earth, they would still travel extremely close to c relative to each other?

My question is this "how does the commander measure his speed"

relative to what ... he could theoretically be boosting his rockets and actually slowing down relative to a gravitational accelleration in the opposite direction. so he thinks he's going faster , but he may just be escaping some supermassive black hole ....what as his marker?If we on earth are discussing him we are his marker.. but thats only relative to us?

I think that for relativistic effects to take place (time dilation, mass increase and lenght contraction) the spaceship have to travel close to c , relative to the space-time continuum. There is nothing special about earth, so why should the spaceships speed be measured relative to us?

Well, from the beginning of this thread, I am speaking about "objects moving away from one another" and not about "the amount of space in between them increasing",

Aha, I misunderstood you in the start of the thred. I agree also that the photon would reach us. It would also offcourse have a speed of c when it did.

Since space-time is getting bigger, shouldn't the EM-field in which the photon is traveling through as a medium also expand proportional to the space-time? Meaning that the photon would have a longer a distance to travel?

So I suppose that even when an object like a galaxy is receding from us at speed faster than C, we are observing the light coming from this object traveling at C. Independently of any "space expansion".

Would the lightbeam ever reach us at all, if space which light is traveling through is expanding faster than the light itself?

For me the bright lines on the detector in the experiment illustrates that the photons energy is concentrated there .

Whereas the dark patches ( wave cancellation), indicates that the energy is absent there.

Why then define a "probability" stating whether it could be there or not!

The formation of bright and dark lines on the screen has nothing to do with the photons energy. (except that the distance between the lines are dependent on the photons frequency) It is interference and probability that creates the pattern. If you sent only one photon through the slits, it could end up everywhere on the screen, but it would most likely end up near the bright lines. "Most likely" is then another way to say "high probability".

If one photon indeed , went through both slits and interfered with "itself"

then its energy has been spread or "smeared out" over an area on the detector.

A photon can be many places at the same time, but it can only be absorbed by one atom at one point in time. Therefore will it not be smeared out over the detector.

Don't know if I understood your questions right. My head is a bit slow

That is the key to my puzzel.

How does one arrive at such a wave function?(many places at the same time).

Understaning this phenomena can be difficult to grasp, as anything else in quantum mechanics. I am really not a particle physicist, but I can tell you the way I've understood it.

When we say that a photon (or electron or other particles) are waves, we have to understand what is actually waving. For example watermolecules waves in crests, sounds waves in contraction, but particles wave in probability. Meaning that a particle is at many places at the same time, but when we look at it, it is a certain probablilty for it to be one place, and a different probability for it to be another place.

My key to accept this fact, was to read about Thomas Young double-split experiment. Are you familiar with that?

If there are many force carriers in the cubic meter what is between the force carriers.

The photons are "smeared" out all over the place, which means that one photon is at many different places at the same time. The photons in a cubic meter will overlap each other, so there is no real place where the photon "ends".

I don't mean to hijack your thread, but I wonder if the probability for a photon to be at a certain place at a certain time is ever = 0? Will it not just gradually get smaller and smaller until it is reaching infinitesimal size?

Thanks mate!

I recently got the high def. version of "Into the Universe With Stephen Hawking" (also featured on that site in a low level res.). The animations in the film are just fantastic in HD. It's on a completely different level than other series about the universe.

The explanations is quite basic stuff though, but I watched it for the graphics.

Anyway, cool site

But how would we tell the difference between a black hole and something that is simply really close to absolute zero?

I don't know, and that was also the reason why I said that someone else have fill me in (check the post) whether it is possible to distinguish it from radiaion emitted from elsewhere than a BH.. aarg.

Thanks for filling in

If by "one day" you mean "billions of years from now when the universe cools to the point where stellar sized black holes are warmer than the background radiation" then sure. Alternately, micro black holes are much hotter and those could be detected via Hawking radiation if we were to find one.

Remember that it is possible in theory to travel great distances in short time. If technology finds a way to exploit worm-holes, we might get much closer to a black hole. The radiation might also find it's way to us through worm holes.

After the dust settles, just what is gravity?

It's funny that the "standard model" is thought to be the most successful description of how all particles and forces interact, but still whenever you ask quantum mechanics about gravity, they're goin' : "Hmm, oh yea, gravity. I'd forgotten about that..uuh, something to do with gravitons"

As you understand, I am no professor, and have not the slightest idea what gravity is on a basic level, except an exchange of gravitons. I'm still waiting for someone to explain it though. I think Einsteins GR is the most elegant theory, but that's only me. I guess someone with more knowledge have to fill in the facts and give us the solutions to the mysteries of gravity.

Einsteins GR predicted them, and that theory has been verified a lot of times.

"Real proof" of a BH is a bit tricky since they hardly emit radiation. Maybe somebody else can fill me in whether Hawkins theory of escaping particles from the edge of the event horizon could one day be detected and linked to being emmited from a black hole?

The way astronomers detect them today is through gravity. When a BH passes our vision of a distant star, it will bend the light from all directions around it, making it look like several similar stars here from earth, when in fact there is only one.

In the theory of general relativity both energy and matter bends the geometry of spacetime which causes gravity, thus if the vacuum energy of empty space is negative, it would bend spacetime in the opposite directions as positive energy or mass, which would be like a gravitational repulsion.

Ok. But in what kind of situations does energy, say photons, bend spacetime? Considering that they lack a resting mass?

It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity.

What does it mean that dark energy interacts through gravity?

what if we could look at it as a balloon inside a ballon, inside a balloon, inside a balloon, et

That reminded me of a story told by Stephen Hawkin. Someone was lecturing a group of people about the cosmos. At the end of the lecture an old lady got up and said "You are wrong. The earth is resting on the back of a giant turtle." The teacher smiled and asked her: "And what is the turtle standing on?" The lady answered: "You're very clever, young man. Very clever, but it is turtles all the way down..."

As StringJunky emphasized, the balloon is an analogy where you have to look at only the surface as the universe. Not in any direction leading away from the balloons material. Think that you were a reeealy smal person living at the balloon surface. You'd see all the other galaxies move away from you as the balloon expands. If you could travel superfast in a straight line, you'd after a while end up at the same place where you started. I think that is also how the universe is expected to work, and one of the reasons we can never reach the end of the universe.

I've seen some images calculated and generated by a computer of how the universe might look like on a big scale. The matter doesn't seem like it's moving in straight lines, probably due to the gravitational influence, and it is spread out pretty smoothly all over the cosmos. If you are asking if the universe itself is moving in straight lines, it's really hard to tell since the fabric of the universe itself is invisible to us.

The universe as a shape is really hard to imagine, atleast from the outside. From the inside it might look like a sphere, but after what I've understood you can't define a center of the universe where the BB occured. If there's no center, then how can it be a sphere?

So as long as no other galaxy is interfering with the milky way, the galaxy will after a period of time turn into a lot of smaller black holes orbiting the super massive black hole in the middle. There will still be lots of dust and free gas hanging around, since the black holes doesn't manage to reach all the leftover matter in the galaxy.

However it is predicted that the Milky-way and Andromeda is colliding in a few billion years, messing up my "prediction" above.

Another thing I was just thinking about. If the dark energy is causing our universe to end in a "big rip", do you think that a black hole would also get ripped apart? I think that it is not so. I don't think a singularity could get torn into peaces, no matter how much energy there is.

Fusion occurs at high pressures and high heat. (?)

Is there a temperature and pressure where the atomic structure breaks down?

Like what followed the "big bang"? The universe was so hot that matter could not exist, would it be conceivable that this is what happens on the 'inside' of a black hole?

The atoms, with all its particles, brakes down already at the stage when the black hole is formed, and that is in fact the whole reason why it is formed. Different kind of pressures are trying to prevent the endless gravitational pull. First the electron- neutron- and the proton-pressure. Then the quark pressure, and finally the preon pressure (if preons exist). After that there is no force known to man that can hold back gravity on such a large scale.

So, Yes, I believe that close to the singularities (beyond the event horizon) matter acts as right after the "Big Bang" when it could not form, and was just a big sea of energy. Inside the singularity itself... I guess we have no clue.

It's been shown that neutrinos are most likely not the dark matter, as the amount of them would have to be tremendously high in order to explain all the DM in the universe, which is 5 times more than all the normal matter.

And how do the gases in the area (hydrogen, etc) not burn up...?

Burning is just a prosess where concentrated heat make some initial ingrediences change into something else. Hydrogenon on it's own will not burn until you get 10^7 Kelvin (right?), and that is also a different kind of burning. Nebulas are far far away from those kind of temperatures, and therefore does not the helium burn.

So the thermal energy of the matter is converted to... ?

I suppose since the laws of physics brake down in the singularities, so does laws of thermophysics.

A black hole is often compared to a whirlpool. Does that mean that in the end, the supermassive BH in the milkyway will suck in all the matter in our galaxy like a vacuum cleaner?

The way I see it the black hole is sucking in the closest material at first. New "food" to feed the hole, gets further and further away. Won't it then at some point be to far away for the BH to have any effect on matter, since gravity is weakening 1/4th for each time you double the distance?

I don't know if I manage to explain what I mean. My head is not made to think about such big things, but I still find them interesting.