More on M 87

In my post regarding the M 87 black hole, I stated that you do not necessarily know what the black hole and its environs look like from that image. The popular image that seems to have taken over the web is just plain misleading because it focuses on radio waves very close to the event horizon. Katherine Bouma, who developed the algorithm that made the picture possible, explained that there were “an infinite number of possible images” that could explain the data, in part due to atmospheric disturbances of different kinds at widely dispersed sites, while the difficulty in getting good data intensity meant that there was an inherent uncertainty. On the other hand, the hole and the ring were valid. However, there is more that the black hole effects.

There is another image obtained from the Chandra X-ray telescope of the environs of the M 87 black hole You will see somewhere near the middle a small black dot that on closer investigation appears to be shaped like a cross. X marks the spot! This is exactly the case. The black hole, the radius of which is almost five times the distance from the sun to Pluto, is too small to register on this image. And whereas the first image was based on radio waves, this is recording x-rays.

Chandra2

As you can see, the effect covers a monstrous volume.

Why Xrays? This is because of the huge amount of energy being lost during a radiation event. To illustrate, a red dwarf star largely emits infrared radiation, and only a relatively low fraction is in the visible wavelength electromagnetic spectrum. Thus Proxima Centauri, which has a surface temperature of about 3,000 degrees K, puts out 85% of its emissions in the infrared spectrum (although flares do contribute some xrays) and its visible emissions are only 0.0056% as luminous as the sun (which has a surface temperature of about 5772 degrees K. Now, consider that five times the distance from the sun to Pluto does not really register on that image, this will give some indication of the power of the black hole. Those xrays are generated from the energy  given off by dust heating as they fall into the regions of the black hole and give off the extraordinary energy of an xray in the spectrum.

The dust accelerates, gets hotter than the surface of most stars as a consequance of collisions, and eventually becomes a plasma that is orbiting the black hole at relativistic speeds.  As an aside, this shows that the science fiction plots of a space ship suddenly coming across a lurking black hole is somewhat improbable. Observation should give good clues well in advance as the size of the Xray emissions around this one is comparable to the distance of most of the farthest stars we can see with the naked eye.

One of the most bizarre things about black holes is that sometimes you can see a jet of material travelling at relativistic speeds away from the polar regions of the black hole. The jets show only a few degrees of dispersion and these can travel up to millions of parsecs. One parsec is about 3.26 light years, so the nearest star to us, Proxima Centauri, is about 1.3 parsecs (4.2 light years) from the sun. The jets can leave a galaxy, and there are images from Hubble where the length of the jet dwarfs the galaxy from which it came. On the other hand, the black hole at the centre of our galaxy does not currently generate such a jet. In the Chandra X-ray image you can see the jet coming out of the M 87 system. (There will be another on exactly the other side of the system.)

This is one of the most powerful events that occur in the Universe, and while we have a qualitative idea of some of what might be powering it, the details are still to be worked out. One theory is that as the plasma spirals into the black hole, the magnetic field gets compressed and rotates, and this magnetic field then exerts a force on the plasma, with the net result that matter is ejected in a jet from the inner regions around the black hole. There is at least one alternative theory. Roger Penrose has proposed that the rotating black hole causes “frame dragging”, which can extract relativistic energies and momentum, essentially from the spin of the black hole. Of course the material being ejected did not come from the black hole, but rather some of the material falling into the black hole is caught before it reaches it and from whatever the cause is ejected at these fantastic energies. The net result is that energy and angular momentum are removed, which also aids the black hole to accrete more mass.

Which raises the question, why does the black hole at the centre of our galaxy not do this? The simple answer may well be that there is no matter close enough to fall in, and what is nearby is in stars that are stable and in a stable orbit. There is a lot we do not know about black holes, and we are unlikely to in the near future.

Is time relative?

In the previous post (http://wp.me/p2IwTC-6m) I gave a simplified account of why time and position are considered relative, in which each observer has his own version of what “here” and “now” means. We need some means of describing what an observer sees. An absolute position would be like GPS coordinates. Everybody agrees where the equator is, and we have made Greenwich a reference point for longitude, but in the general Universe there are no obvious reference points. Without a reference point, “here” is meaningless unless expressed as a distance from something else, and this has been well established since Galileo’s time, if not earlier. There was thought to be “aether” through which everything travelled, but Michelson and Morley provided evidence there was no such thing. The formalism of Einstein’s relativity puts time in a similar position, and it dilates as velocities approach that of light. This is accounted for with what is called “space-time”, in which time is just another relative coordinate.
All observed evidence is in accord with this, and an example is the lifetime of muons. The muon is an elementary particle that decays to an electron with a half-life of about 1.5 microseconds. However, if the muons were travelling at about 98% the velocity of light, applying the Lorentz-Fitzgerald factor for time dilation, as required by special relativity, it has been shown that this half-life is about 5 times longer, and most importantly, muons behave as if they live five times longer when travelling at such velocities. From an observer considering the muon’s point of view, the reason it lasts longer is because the distance it thinks it has travelled is shorter. This suggests that time is relative, and the equations of relativity invariably give the correct prediction of a measurement.
Consider a space traveller. According to relativity, if the traveller heads off at near the speed of light and travels far enough, then comes back, time has essentially stopped for the traveller, but not for whoever is left behind. That was the basis of my scifi trilogy “Gaius Claudius Scaevola”. Within the trilogy, Scaevola starts in Roman times, gets abducted by aliens, and returns sometime like the 23rd century, and he has aged a few years only. The principle of relativity is that all clocks in a moving ship must slow down equally; as Feynman remarks in Six not so easy pieces, if this were not so, you could use something like the rate of development of a cancer to work out the absolute velocity of a space ship. To further quote Feynman, “if no way of measuring time gives anything but a slower rate, we shall have to say, in a certain sense, that time itself appears to be slower in the space ship”. The best-known application is the GPS system. Without the equations of General Relativity, this simply would not work.
Nevertheless, I believe there is a way of measuring an absolute time. Suppose a similar traveller headed off to a galaxy five hundred light years away at light speed, and, in accord with relative time, came back a billion years later without having aged. Now suppose he and another physicist from the future decided to measure the age of the Universe, that is the time from the big bang. The equipment is set up and gives a meter reading. Surely both must obtain the same reading since they see the same dial, yet according to the traveller, the Universe should be only13.8 billion years old, while the measurement gives it at 14.8 billion years old. There is only one possibility: the Universe is 14.8 billion years old, and all that has happened is that the traveller has simply not observed the passing of a billion years. The point is, when considering distance, there is no reference position. When considering time, there IS a reference time, and the expansion of the universe provides a fixed clock that is a reference visible to any observer. Worse, you could in principle work out the age of the Universe from within the ship, so in principle you could use this to work out the speed, apart from the fact that determining the age of the Universe is not exactly accurate. So why does muon decay slow?
Suppose we start with no muons, then at time t we shall have nt muons, given by (assuming the number of decays are proportional to the number there)
n_t=n_0 e^(-kt)
Now it is obvious that you get the same result if either k or t is dilated.
What is k? It is the “constant” that is characteristic of the decay, and it can be considered as the barrier to decay, or the tendency of the particle to hold together. Is there any way that could change? Does it have to be constant?
This gets a bit more difficult, but Einstein’s relativity can actually be represented in a slightly different way than usual. For those with a grasp of physics, I recommend Feynman’s “Six not so easy pieces”. When Feynman says they are not so easy, he is not joking. Nevertheless one point he makes is that Einstein’s special theory of relativity can be represented solely in terms of a mass enhancement due to velocities near the speed of light. What that means is that as the muon (or the space traveller) approaches the speed of light, it gets more massive. If that energy is concentrated on the muon, then the added mass might dilate k by increasing the barrier to decomposition. It is not necessarily time that is changing, but rather the physical relationships dependent on time. Does it matter? In my view, yes. I would like to think in science we are trying to determine what nature does, and not that which happens to be convenient at the time.
In many cases in science, like the equation above, there can be more than one reason why an equation works. Another point is that the essence of a scientific theory should be able to be conveyed without the use of difficult mathematics, although, of course, to make specific use of the concepts, difficult mathematics are needed. What the scientists should do is to ask questions of a theory, and then test the answers.
As an example of such a question, we might ask, did Michelson and Morley really prove there is no aether? My view is, no they did not, although that does not mean there is aether. The reason is this. If light always has the same velocity relative to the aether, it must interact with it. That means there is an interaction between aether and electromagnetism. Now molecules have local electromagnetic fields, and such molecules travel fast and randomly, and might very well “trap” aether. Think about a river flowing, with reeds along the bank. The water flows strongly, but if you try to measure the flow in a reed-bed, the water is virtually stationary. In the same way, the random motion of air might trap aether near the earth’s surface. What science suggests now is simple: repeat the Michelson Morley experiment outside the space station. Suppose the answer was still zero. Then Einstein’s theory is firm. Suppose the answer is not zero? Actually, the equations of Einstein’s relativity would not change all that much, and would actually become a little more complicated, but the differences would probably not be discernible in any current experiment. What do I think? That is actually irrelevant. The whole point of science is to ask questions, to try and uncover further aspects of nature. For it is what nature does that is relevant, not what we want it to do. What do you think?

Space warfare

For some reason, there have been a number of articles on the web recently on the realism of fictional space wars. Some of the points in fiction are obviously wrong, thus space vehicles travelling in a straight line do not need to have motor firing, and using wings to bank and turn is, well, just plain wrong because wings do not do anything in a vacuum. On the other hand, the purpose is to be entertaining, and in a film, being technically correct my merely leave the average viewer wondering. But what about in fiction? Technical explanations may turn off many readers, while correct physics without an explanation may just seem to be incomprehensible.

I had this problem in my ebook, Scaevola’s Triumph, which is now available from Amazon. This concludes a trilogy and the basic plot is that the planet Ulse is losing a space war and faces extermination. However, the future has engineered a small party of Romans to be abducted by aliens so that Scaevola could save Ulse by turning around the war. It may not seem realistic that an ancient Roman could change anything, and that is what the Ulsians believe too, nevertheless he can, and can you see why?

The purpose of the first two books was to show how science works, and what it is like to make a discovery, so it was important to try to get the science right in this book, particularly with the battles. So, what would a space war look like? If you are writing a story where you need a space war, you have to take some liberties, if for no other reason than to keep the story interesting. The first point is that distances would be very great, and would extend over light centuries. This had the problem for my civilization in that if an invasion force could travel near the speed of light, and they deployed enough military force, the invasion could proceed at near the speed of light, and hence the civilization would lose most of its dominions in that direction before they even knew there was a war. Actually, this problem first occurred with Alexander, who moved about as fast as a messenger sometimes.

What scientific issues arise in a battle? One issue is relative velocity. If two vessels are going in opposite directions, the time they have together is trivial. In one battle in my book, it took hours to approach, and a few seconds in a battle zone. Since such short contact time is undesirable, ships attacking others in my wars usually spend much of their time slowing down. Even then they might pass through the enemy, and then take at least half an hour to turn around and come back. Looping around the back of a planet is a good way to turn.

What about weapons? My view is that lasers are useless because if you depend on them, the enemy merely has to get bright and shiny, and reflect the energy. One solution is to fire otherwise undefined constrained bursts of mass/energy approaching light speed. They are difficult to avoid because the energy arrives almost as soon as the light signature of the firing. Some people have suggested that small pieces of matter are all that is needed. Chaff hitting your ship fast enough will do extreme damage. However, if ships are capable of travelling at velocities approaching light speed, they must have some means of dealing with bits of rock, etc, so that will not work. (The fact you do not know how they could do it is beside the point; we do not know how to approach light speed either, but if we did, we must have the other.) I have also seen criticisms of “fireballs”. Strictly speaking, fire cannot occur, but if you see fire merely as a plasma, then there is no reason why jets of metal vapour in a plasma could be realistic. Of course, in science fiction you can be inventive. The weapon I “invented” is one that within a locked zone the weapon exerts a field that changes the value of Planck’s action constant on a given vector direction. All nuclear structure on that axis disintegrates. Defend against that! (I know – a variable constant is uncouth, but then the question arises as to why it is constant. We don’t know that there are no circumstances when it could not have another value, do we? And this is fiction.)

Science fiction also has the “cloaking device”. In my space war, that is there – all electromagnetic radiation that strikes the vessel is absorbed and re-emitted on the other side, on the same vector. (Really, more a chameleon device.) Now, supposing there were an enemy using such a technology, how do you defend against that enemy, which means, how do you locate him? There is a way of seeing ships using such technology. Can you work it out?

Yes, it is all fiction, and I am sure that there are a number of faults there too, but the question then is, is it entertaining, and does it encourage anyone to think? If so to either, then it was worth writing it.