Neil9327

Trying to escape from past the event horizon would take an infinite amount of energy.

For this to be the case in my scenario then as work required to pull camera out = integral of force over distance then since distance is finite (it is less than half the orbital diameter of the orbiting mothership) then force would have to be infinite at some point(s) near the event horizon. But as I stated earlier an astronaut falling through would not notice significant tidal forces/spagettification effects until well inside the event horizon (for a supermassive black hole). So this would indicate that the forces are not infinite. So the energy cannot be infinte.

Where am I going wrong in my understanding?

no, you couldn't. the wire would be held together by electromagnetc interactions between the molecules.

 

even if the tensile strength was for all intents and purposes infinite below the horizon, the photons that mediate the force wil be sucked into the hole before interacting with the other molecules.

But just below the event horizon of a supermassive black hole the tidal forces are quite small and the gravitational force would be relatively small (but over a large distance from space a high negative potential energy) so at any point in the string surely photons etc would work nearly normally with regard to providing strength. After all they do say that if you are falling into a black hole through the event horizon of a supermassive black hole you would not be obviously aware of it, so the photons are doing their job there.

OK in that scenario you are not accelerating, but for supermassive the value of g is quite modest anyway

Just a thought experiment. If you were in a heavy spacecraft in orbit around a supermassive black hole a comfortable distance outside the event horizon of a black hole then would it be possible to lower a camera on a length of string, recording at the camera, down into the black hole (deeper than the event horizon) and record what it sees, before retreiving it for viewing by pulling it back up with the string.

The camera would have rocket motors to make side-to-side adjustments if necessary (to keep the string straight and radial to the orbit).

It would obviously assume a very strong and long piece of string, of low mass.

As it is a supermassive black hole the spagettification effects would be small.

I am a physics graduate, so I know a little. But I have forgotton most of it in the past 20 years.

I had the following thought experiment that I thought I'd share with you.

If you have a glass tube of hydrogen at 1 atmospheres pressure 1 meter in diameter 1000 light years long but with open ends then in the middle for quite a long time the hydrogen would remain stationary, because the escape pressure of the hydrogen would not reach the middle of the tube for many years.

Now increase the pressure of the hydrogen so that its density is high enough to have a noticible gravitational effect. Would this gravitational pull pull the hydrogen from one side to the other? No because at each point the influence of each side would be almost the same (the difference over 100 light years would be negligible).

Now increase the mass of hydrogen so that the centre of the cylinder has a gravitational potential energy to be so low that it becomes a black hole. Then surely you have a linear black hole that extends for 1000 light years.

Now take that black hole "string" and loop it round so that it forms a perfect circle, diameter 130 light years. Would this structure persist? Well there would be some faint gravitational force causing it to collapse into itself. But would this string have any longitudinal compression strength that might offset this shrinking.

And what if the whole thing was rotating? Would the centrifugal force cause the black hole "string" to stay in place?

So is it possible that there might be lots of black hole "strings" or "tubes" floating about space waiting to STRIKE!

Take a TV remote control and look at its front end and press a button. Can you see anything? No.

Now do the same but look at it through a camera phone. You can see it flickering!

Amazing huh.

At the Event Horizon one could say that space itself is flowing towards the singularity with the speed of light.

 

Any object placed there will be forced towards the Singularity, like a boat in a very current river.

 

If a flashlight is pointed outwards when it passes the Event Horizon, then the light will move outwards with the speed of light, but space itself is moving with the same speed in the opposite direction. The photons will be brought back by space, just like the boat with a too small engine, struggling to get upstream but actually goes downstream.

 

If the flashlight is in freefall towards the Black Hole it will continue to interact with itself and keep on shining until it breaks from the strong tidal forces.

Interesting. But is this true?

With some supermassive black holes they say that the event horizon is far out from the black hole itself, such that the amount of gravity at the event horizon is not actually all that strong, but that the distance between it and outer space where the gravity is small, is much larger than for other black holes (so that the gravity * this huge distance > speed of light escape velocity).

So if you are falling through the event horizon and are holding a torch in front of you, then before you fall through you will see the light from the torch of course. Are you really suggesting that as the torch passes through the horizon first, the light will suddenly stop being visible to you?

And then once you are through, does the light reappear, to you?

To quote Wikipedia on Supermassive black holes:

"The tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astronaut travelling towards the black hole center would not experience significant tidal force until very deep into the black hole. "

So if you do not experience significant tidal forces, does the light really experience the event horizon as a true barrier to you, being right next to it?

I understand that it is not possible for light to escape a black hole because the escape velocity is higher than the speed of light, which it cannot achieve of course.

But if you are, for an instant, just inside the event horizon, say a millameter, then light shone out WILL cross the event horizon, albeit perhaps to only a millameter or so outside it. I say this because a craft may not have sufficient velocity to escape the earth's gravity, but launched upwards it WILL go up for some distance before falling to earth.

So could you not have a chain of devices, a camera on the first. The camera takes a photo inside the event horizon, sends the data out to the next device just outside the event horizon, and so on up back to earth. Thus allowing us to see what it looks like inside a black hole.

I'm just curious. Don't please go to great lengths to answer this!

Edit: Just to re-emphasize my point: If you have a space ship that is launched from earth it might have insufficient velocity to escape the earth's gravity, but it WILL be able to go up some distance.

Thereby by analogy, surely if a light beam launched from within the event horizon may not be able to escape from the black hole under its own steam, then can it not go up some distance - a few meters perhaps, analogous to the space ship.

After all, the event horizon is an arbitrary barrier - it is only the point at which light cannot under its own steam leave the black hole completely, it does not say anything about travel local to itself.

Or does it?

How do you explain the selective dithioketalization of the Wieland-Miescher ketone on the unsaturated ketone?

Similary the saturated ketone can be selectively protected by 1,3-propanediol. Almost similar conditions can be used, pTsOH in AcOH for the ketalization or in benzene for the other one?

Is it Hard and Soft postulate? If yes or maybe why the thiol does not add onto the beta carbone of the unsaturated positon?

Thanks for your suggestions.

3 years ago I got pitting edema (pitting oedema) on my left foot. This is a swelling caused by the buildup of lymph fluid. I had not had surgery, or heart failure, so the only possible cause of this, that I can find, is DVT deep vein thrombosis.

But I have not been on any long haul flights. So could I have got it by sitting for hours on a chair surfing the net (scienceforums of course).

The problem is that this edema swelling makes the foot vulnerable to bacterial infection, and this put me in hospital for a week last week.

If a civilisation living on a planet orbiting a nearby star a few light years away detonated a 50MT thermonuclear bomb in space near the planet with direct line of sight to the Hubble space telescope, say, would the explosion be detectable by Hubble in any way (visual, gamma ray burst, infra red, x-ray)? (assuming we knew it was coming and were ready for it).

And if so could they, and us, use this method to communicate with each other in a form of nuclear "morse code" using several bombs (albeit with a 4-year period waiting for the reply).

I presume that no lasers or other man-made radio waves could carry that sort of distance and still be detectable?

If you put square miles of tin foil behind the bombs you could focus its energy in one direction.

Most bad backs heal themselves. However, it won't do any harm to get it checked if you are worried. Just don't go to a chiropractor. Your back does not need potentially damaging voodoo massage. If you are really worried, find a suitable medical specialist.

 

If there is nothing specifically organic wrong with your back, as shown by your specialist's test results, the best advice is to carry on with normal life, just avoiding any activity that causes pain. When the back pain is gone, begin with gentle back exercises, and slowly build them up till your back is strong.

Just to provide a bit of balance to the discussion, I have personally found Chiropractors to be very effective. They are not damaging voodoo massage artists.

Students teaching the class. isn't that like lunatics running the asylum?

Seriously though I think that is a good idea, as long as you can persuade the teachers that you can maintain discipline and a steady work-rate in the class.

Following on from the above post, I mentioned this idea to a mate, and he said that these generators would add to the tidal drag and would slow down the moon in orbit round the earth even more, possibly causing it to crash down onto the earth.

He's talking nonsense isn't he?

Ammonium Nitrate is an explosive isn't it?

Isn't there a risk of it blowing up if you crystalize it, and start bending it?

"An increasingly large number of observations consistently reveal the existence of a much larger amount of intergalactic matter than presently accepted. Radio signals coming from directions between galaxies is discussed. An average density of matter in space of about 0.01 atom/cm3 is derived."

http://www.newtonphysics.on.ca/UNIVERSE/Universe.html

 

That's about 10 atoms per litre.

So if mankind does find itself able to produce a spaceship that can travel at, say, a quarter of the speed of light, I wonder what effect these atoms would have on drag - there would need to be a constant power applied to the craft to overcome this.

Also since these are unlikely to be still, I wonder whether they could be used to propel craft along? probably not.

Well PHP CSS yes they are good. However if you are looking to do web site programming and earn money you might want to learn Microsoft .net and the C # (sharp) programming language. They are more GUI based so are, IMHO, more flexible.

he would not be able to as his 'past self' would be there and since he doesn't remember swapping places with his 'future self' when he wrote on the paper means that it never happened and john would have seen an A.

I suppose that's the point about time travel: It is possible, but those travelling cannot take with them the information they learned in the "future".

So causality is preserved.

So the film "Back to the future" was incorrect because the guy who went into the past could not have known that the couple courting were his parents, so would not have got into a panic about it.

No sorry I don't think I phrased my question correctly. I am asking what is the density actually at a random location in deep space, not including the stars in the calculation. So if you take a meter cube in deep space, how many atoms will there be in it on average?

Of course since nothing man-made has been outside the solar system I guess this is hard to know. But I would have thought the figure would have been lower for space between stars than for space in our solar system. And higher than between galaxies.

Or to pose another question: In the most empty part of the universe, how far away is the nearest atom?

Question: In deep space (between stars but within the milky way, but away from stellar clouds etc) I guess there are a few scattered atoms. What is the average distance between atoms there.

The size of the black hole determines how strong the tidal forces are at the event horizon. For a large black hole, it would hardly be possible to feel these tidal forces and for all black holes of practical size, the tidal forces on atoms are neglectable.

so does that mean that if you were falling into a large black hole you might not be aware of this until later?

I suppose if you were falling in you would be able to see light coming from within, but not far within the event horizon.

I believe I am right in saying that any item, such as a metal coin, would become a (very tiny) black hole if it could be compressed to a small enough size? So if we could compress a nucleus small enough it would become a very tiny black hole with very strong tidal forces, and if we then fired two protons at it it might release some energy?

How about the following scenario:

Two people John and Mark are in a room with a piece of paper.

Mark writes a letter A on the paper, and John witnesses what is written.

The following day Mark goes into a time machine to take him back to the previous day. He remembers that he wrote a letter A and instead writes a letter B, again with John witnessing.

Two days later someone else asks John what he saw being written. Did he see an A or B?

Just an idle question:

If a mass of uranium (with neutron source) fell in to a black hole, would the forces/pressures on it shortly before reaching the event horizon be sufficient to make it supercritical and detonate in a nuclear fission explosion?

Similarly if you had some deuterium/tritium (without the uranium) and did the same, would you get a fusion thermonuclear bomb?

I believe that the approach towards a black hole is to cause elongation and narrowing.

Perhaps that could be a way to detect the presence of black holes in the future?

the language used by people in their day to day lives reflects their own experiences, which is life on earth only. Where weight is always proportional to mass.

If societies started living on the moon as well as on earth then language would start developing different words for them.

Totally agree.

Other ideas:

Keep things simple

Get the basics right (don't get side tracked)

Time is the only currency we really have - use it wisely

Don't work too hard. Or too little.

Never make assumptions.

Think Big, but Act Small

Don't belive in luck

Act rationally, not emotionally

Oh and remember me when you make your first billion

I'd have thought that a more common sense explanation is that it is equal to

[math]

\lim_{n\rightarrow \infty}\frac{n}{\sqrt{n^2+{\sum_{n=1}^{\infty} n^2}}}

[/math]

where this isn't a normal sum symbol - it goes from 1 to infinity but does not include the value n provided externally.

So since this means that as n increases the bottom half will progressively get larger than the top, so at infinity the result will tend to zero.