JEROME - Black holes do not exist

[Olowkow]

Take a very long thin object, and see if there appears to be a torque on it. If not, try it at 90 degrees, just in case you had it accidentally aligned the first time.

This is where it gets tricky, and I read about this a long time ago, but I think IIRC, that stuff like foreshortening gets in the way of this experiment. I think there is an experiment to detect the center of mass (in the case of gravity vs. acceleration), but not sure about this one for weightlessness. I defer to the experts at this point.

 

[lenny]

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html

from your link:

In addition, however, virtual particles aren't confined to the interiors of light cones: they can go faster than light! Consequently the event horizon, which is really just a surface that moves at the speed of light, presents no barrier

this seems pretty sloppy talk, no?

pair creation near the EH hardly counts as "going faster than light"

and even if one insists on calling the EH a surface, in what sense is it "moving at the speed of light"?

 

[Terry]

This is where it gets tricky, and I read about this a long time ago, but I think IIRC, that stuff like foreshortening gets in the way of this experiment. I think there is an experiment to detect the center of mass (in the case of gravity vs. acceleration), but not sure about this one for weightlessness. I defer to the experts at this point.

Tidal forces definitely act on things in free fall, if there is a gravitational gradient present. Which there certainly is in orbit around the earth. If you were in an area where there were no significant gravitational forces, so that your geodesic was a eucalidian straight line, there would be no tidal forces observed. The equivalence principle as I understand it says there is a local equivalence between gravitational effects and acceleration. Having a long stick on your spacecraft is "cheating"

 

[Olowkow]

Tidal forces definitely act on things in free fall, if there is a gravitational gradient present. Which there certainly is in orbit around the earth. If you were in an area where there were no significant gravitational forces, so that your geodesic was a eucalidian straight line, there would be no tidal forces observed. The equivalence principle as I understand it says there is a local equivalence between gravitational effects and acceleration. Having a long stick on your spacecraft is "cheating"

Not sure I follow. Certainly having an accelerometer on board would measure slight bumps in the mass of the earth, like mountains. This is my understanding of why they call it "microgravity". Is this what you mean by tidal forces? Why is having a long stick cheating?

I totally agree that orbiting is a form of acceleration, and free fall. I know there have been all kinds of ideas for distinguishing the local equivalence, but it is not a trivial problem, and I don't know if any of them are true.

 

[Terry]

A long stick is cheating because it is long, so your experiment is taking up a significant-sized piece of space. So it isn't "local" any more. As for tidal forces, this is what I'm talking about: http://en.wikipedia.org/wiki/Tether_propulsion#Tidal_stabilization

 

[Olowkow]

A long stick is cheating because it is long, so your experiment is taking up a significant-sized piece of space. So it isn't "local" any more. As for tidal forces, this is what I'm talking about: http://en.wikipedia.org/wiki/Tether_propulsion#Tidal_stabilization

Thanks, this seems to be the answer to my question. So this would orient itself toward the center of the earth if in orbit, whereas it would not orient itself to anything on a trip to Mars.

An attitude control tether has a small mass on one end, and a satellite on the other. Tidal forces stretch the tether between the two masses. There are two ways of explaining tidal forces: In one, the upper part of an object goes faster than its natural orbital speed, so centrifugal force stretches the object upwards. The lower part moves slower than the orbital speed, so it pulls down. Another way to explain tidal force is that the top of a tall object weighs less than the bottom, so they are pulled by different amounts. The "extra" pull on the "bottom" of the object stretches it out.

 

[The Man]

TheMan:

When talking of experiments to distinguish acceleration from gravitation it is common practice that it is taken for granted that there is no communication from a "local frame" to the outside world. Looking out the window requires communication via photons. Even a beam of light in an accelerating "elevator" in space which horizontally crosses the room will appear to be deflected "downwards".
The question remains, how does one distinguish experimentally between being in orbit and simply traveling in a so called "straight line" in space, where weightlessness is concerned?

Yes for those experiments demonstrating the equivalence principle “isolation” is critical, as MM points out.

This is correct, if you are inside of a FoR that you unable to see beyond (hence the term, "isolated"). For all practical purposes, in this case the two are equivalent. However, since we have the capacity to observe the ISS from outside its FoR, we can clearly see that gravity is still acting upon it. If gravity were not acting on it, then we on Earth would observe the ISS to fly off into interplanetary space due to its inertia.

There are other ways to verify this as well. For example, gravitational time dilation - the clocks on the ISS will run at a slightly different rate compared to the clocks on the Earth due to the fact that they're inside the gravity well of the Earth. But then, this would mean being able to make comparative measurements between the two FoR, which would be impossible in a completely isolated system.

However isolation is not the norm and that particular quote from me was about weightlessness or the apparent lack of a gravitational force (specifically the ISS which has windows) and not about equivalence experiments in isolated reference frames, sorry if I did not make that clear.

no. but i thought i met your definition of weightless, and we agree i would not be weightless in that case.

What definition of weightless did I give?

Yes, we do agree that you would not be weightless when stationary in a gravitational field.

it cannot.

But how might something accelerating in a circle be weightless?

You only seem weightless or if you prefer perceive weightlessness, just as you would in the falling elevator. However in both cases you are still accelerating due to the force of gravity which is what we specifically define as weight.

ETA: not the acceleration but the force.

 

[Paul]

pair creation near the EH hardly counts as "going faster than light"

and even if one insists on calling the EH a surface, in what sense is it "moving at the speed of light"?

This seems to be why, just don't ask me to explain it...

The event horizon is what, in relativity parlance, is called a "lightlike surface"; light rays can remain there. For an ideal Schwarzschild hole (which I am considering in this paragraph) the horizon lasts forever, so the light can stay there without escaping. (If you wonder how this is reconciled with the fact that light has to travel at the constant speed c-- well, the horizon *is* traveling at c! Relative speeds in GR are also only unambiguously defined locally, and if you're at the event horizon you are necessarily falling in; it comes at you at the speed of light.)

from http://antwrp.gsfc.nasa.gov/htmltest/gifcity/bh_pub_faq.html

 

[sol invictus]

I noticed you completely avoided all the Black Hole stuff as well. Quit acting like those you criticize for avoiding a conversation.

I don't see the point in trying to explain advanced concepts to you when you don't understand high-school level Newtonian dynamics:

Things that are indeed free falling are accelerating the entire time. The ISS is not, any more than the moon is.

If you just consider the ISS, or any other body, in an orbit like the moons, you can see how ridiculous the concept is. An orbit is not the same as free fall. No matter how many web sites say it is.

It is very common misperception.

In any case, your question on black holes was so full of wrong statements that it's difficult to answer without correcting them all first (which I'm not going to do, at least not so long as you keep acting this way).

Is your question why a BH can have an electromagnetic field when it also has an event horizon?

 

[sol invictus]

This seems to be why, just don't ask me to explain it...

Yes, that's correct.

Close to the horizon of the black hole the geometry is very close to ordinary flat space. The horizon is literally the surface swept out by a planar sheet of light moving away from the center of the hole (planar because you are too close to the horizon to notice that it's a sphere).

 

[Paulhoff]

Things that are indeed free falling are accelerating the entire time. The ISS is not, any more than the moon is.

If you just consider the ISS, or any other body, in an orbit like the moons, you can see how ridiculous the concept is. An orbit is not the same as free fall. No matter how many web sites say it is.

It is very common misperception.

In common speech, the term acceleration is only used for an increase in speed; a decrease in speed is called deceleration. In physics, any increase or decrease in speed is referred to as acceleration and similarly, motion in a circle at constant speed is also an acceleration, since the direction component of the velocity is changing.

So, One the moon and ISS are acceleratiing and Two they are in free fall no matter how many times you say they are not.

Paul

 

[MattusMaximus]

Been lurking here. I always get a chuckle out of the threads where robinson thinks that he can teach me and Sol physics...

ETA: For anyone (including robinson, should he choose to) interested in learning some of the basics about these topics concerning apparent weightlessness and orbital motion, check out this link...

http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/vectors/sat.html

 

[Belz...]

If this is so, why is the universe expanding at an increasingly accelerated rate?

Should not all matter be coalescing due to gravity?

JEROME, considering how militant you are about this issue, shouldn't you at least know something about it ?

The universe is EXPANDING. Gravity IS pulling matter together, but the SPACE between them is expanding more quickly.

 

[Belz...]

Make believe!!!

Dark energy is the make believe that is used to justify the theory in spite of the data.

Then by all means, JEROME, present an alternative.

 

[Herzblut]

The universe is EXPANDING. Gravity IS pulling matter together, but the SPACE between them is expanding more quickly.

I don't understand. If gravity pulled all matter together, space could not expand. It would contract.

 

[Reality Check]

I don't understand. If gravity pulled all matter together, space could not expand.

The expansion of space is space actually expanding.
Gravity though acts on matter and so forms stars, planets, galaxies, etc. This is a local effect so that we detect galaxies moving away from each other through the expansion of space but do not notice it on smaller scales. For example the expansion of the space that the Earth occupies does not result in the Earth becoming larger because gravity dominates.

 

[Belz...]

In case it is hard to wrap your mind around the concepts. The ISS is not falling towards the earth. If it were falling, due to gravity, it would be accelerating. Which is very much is not.

Oh, really ? How is it not accelerating, exactly ? Not accelerating means it's going at a constant speed in a straight line, no ?

 

[Herzblut]

The expansion of space is space actually expanding.
Gravity though acts on matter and so forms stars, planets, galaxies, etc. This is a local effect so that we detect galaxies moving away from each other through the expansion of space but do not notice it on smaller scales. For example the expansion of the space that the Earth occupies does not result in the Earth becoming larger because gravity dominates.

Right.

What I say is that first of all gravitation is not a local effect, but a large scale phenomena with infinite range. Secondly, I tried to say that matter creates space, without matter there's no space. If matter in Universe was pulled together on a cosmical scale, space would not be expanding but contracting, following matter.

Matter and space cannot be regarded separately.

 

[Belz...]

Free fall has a specific meaning, and it is not what the ISS is doing. It is in orbit. It would be just as wrong to say the moon is in free fall. Nonsense talk.

"la la la la la !!"

 

[Herzblut]

Oh, really ? How is it not accelerating, exactly ? Not accelerating means it's going at a constant speed in a straight line, no ?

What is a straight line in curved space-time?