Out sun has a lifre time of about 10 billion years. A massive star burns its fuel up much faster than our sun and lasts for only a few million years. Such a star that existed a billion light years from us could have burnt out 5 billions years ago. I imagine that we would not be able to see that star. Its light came through the solar system and went past us long ago. What about the cosmic background radiation? It comes from a small opaque universe that existed about 12-14 billion years ago. That radiation dominated universe lasted less than a million years (I think). Will the CBR stop coming through the solar system at some time in the future? Why hasn't is bypassed us already? It appears to be coming at us from all directions? Can somebody describe the World Line of a photon from the CBR? The balloon analogy description of the expanding universe does not help me with the above. Is there a better analogy?
The CBR will not cease to crackle because it's assumed the our universe expands in proportion. Imagine a blank page and blot of india ink expanding on that paper. Now imagine a point in its center with an ear. Assuming there are sounds emmanting from that ring, as long as that ring exists there is crackle. And as long as that ear exists too, there's crackle being heard. There seems to be enough mass in the universe to keep the the balance of expansion and collapse at a stalmate, so to speak. Translate this to the notion of space time, and Einstein could very well have been right. If there were no 'fabric' property to the idea of what space is, then that noise so long ago should've either bypassed us by now or died out long ago. Just as you could feel the ink of the of inkblot and hear it were it to crackle, perhaps in the micro world all those eons ago seconds before the supposed bang you could "feel" space too.
and as far as world lines- In terms of the CBR and what it's got to do with it, I'm not sure what your question is but where the theory itself is concerned you see the proof of it every time you take a picture or use a camcorder. And its not only that you imagine there would be no star there had it died out 5 billion years ago, its that you are right. The belief is that half those sparkly things we see up there at night aren't even there.
Gendanken: I am aware that some (many) of the stars seen today might not exist any more. Some are certainly not where they seem to be. Your ink & paper analogy do not do anything for my understanding. I mentioned a star 1 billion light years away that ceased to exist (or stopped radiating) 5 billion years ago. I imagine that we cannot see that star now. This was mentioned as an introduction to my real question. My question is about Cosmic Background Radiation which was emitted by our early radiation dominated (and opaque) universe. That condition lasted less than a million years about 12-14 billion years ago. Why/How do we still see the CBR? Your explanation seems to imply that the universe expands at the speed of light, since the CBR travels at that speed. There must be some other explanation. I mentioned World Lines because World Line diagrams sometimes make SR & GR concepts a bit clearer.
Ok- I may understand what you're getting at this way: You're curious as to why it is that, say, a star dying 5 billion years ago lets a light out that crosses the universe towards our spot one billion light years away and we still get to see it. Dinosaur: I feel that light should have passed us by now and should be 4 billions light years behind us. Gendanken: Not so. Consider Olber's paradox. It concerns the idea that if the space were infinite, sprinkled all over with stars AND NOT expanding, the night sky everywhere should be ablaze with stars. So it follows: If I took that inkblot and contained it so THAT IT WOULD NOT SPREAD on the paper, placed you in the middle and sprinkled the whole thing with dandruff, you would look up in your inky sky and see every last flake. If I placed small radios all round the circumference of that same blot with the soundwaves converging towards your center, your radio frequencies would be riddled with sound. Say the light and sound from both these things took 100 years to reach you. If I kill them off now, it will be 100 years before you know it. No light source, no light. No sound source, no sound. At 101 years a blank sky and silence. But that's only becuase I CONTAINED the ink blot, remember? Say I let down the hatches and let the ink blot run at 'c'. Knowing that light travels at finite speed and assuming our wonderful universe is expanding at 'c'......there's a stalmate. That 'final batch of light', so to speak, letting you finally know that the thing you're looking at is actually quite dead never reaches you. Every second there's new space to cover. The 'final batch of sound' letting you know its all over has just such a hurdle. It never gets there. You know what? Its not that physical laws change in any way on the macro scale and we know that, but really think how ironic it is that in order for you to make a circus of the our logical, perfectly commonsense laws all you have to do is simply throw them as they are into a place where NOTHING, absoulutely NOTHING ever stands still- space. Better now? Hey....still awake? Yoo hoo........
Gendanken: Concerning your question: Yes, I was a mainframe programmer for over 40 years. I was a programmer back in 1951-1952, but did not program anything similar to a mainframe until about 1955. My early work was for the Air Force Intelligence in the early days of the cold war (1951 to 1954). They used a gadget called a card programmed calculator. Some engineers at an aircraft company had worked with wire cutters and soldering irons, hooking together several punched cards devices. The company’s accounting department had been renting from IBM, who sued due to what they considered damage to their equipment. The aircraft company claimed they were only liable for the cost of the equipment, which they were willing to buy. The result of the lawsuit was a settlement. IBM paid the aircraft company and the engineers a lot of bucks. It seems that the engineers had patented their idea, which turned out to be a damn good one. IBM bought the patent so they could use the concept. They ended up in the odd position that winning the law suit would prevent them from ever using the idea. In order to win they would have to claim that their equipment had never been intended for such use and would never be used that way by IBM or its customers. The CPC was a damned Kludge. It had hardly any memory, perhaps a few hundred bytes. Punched cards containing data and instructions were feed in, with results going to a printer or punched cards. To solve 20 equations in twenty unknowns, the program read the set of equations from punched cards, which also contained instructions. The initial output was another set of cards with slightly modified equations. After 20 passes, the final set of cards had the solution vector. Due to the small amount of internal storage, most programs used punced cards to store intermediate results. The cards would be manually fed back into the system. Since the system did not have enough storage for much of a program, the initial program punched instructions onto the cards with the data. Each card contained both data and instructions Programming that kludge involved changing the wiring of what were called plug boards as well as writing instructions and data to be punched into the initial set of cards fed to the system. The plug boards were analogous to the hard wired circuitry of a modern computer. Wires with plugs at both ends were used to connect logical components, allowing the system to have a different architecture for each program. By about 1955, I was working for the Burroughs corporation with Von Neuman type computers, whose architecture was similar to what we work with today. The memory was on a magnetic drum with far less capacity (about 20,000 bytes) and much less speed (2 milliseconds per command). Magnetic tape was used for large files of data. I would not even call that system a mainframe, which implies a system with far more speed and capacity. Programming in VB 6.0 is a dream compared to working with numeric machine code, punched cards, and plug boards. The first assembly language was a quantum leap in programming tools. Even the early compilers were clumsy compared to VB. BTW: I once wrote the first version of an assembler in assembler code and had 2-3 clerks manually create the machine code by emulating what the assembler would have done with the source code. That effort resulted in the initial machine language version of a primitive assembler. That primitive assembler was used to create the more complex final version of the assembler. Back to cosmology: Your ink blot analogy does absolutely nothing for me. The expanding balloon analogy helps some (see below). I was hoping for a better explanation/concept than what I have been able to imagine. BTW: I am familiar with Obler’s paradox (note spelling), and do not think it is relevant here. I cannot believe that a star 1 billion light years away can still be seen if it ceased radiating 5 billion years ago. How about a star 10 light years away that stopped radiating 1 million years ago? Could we still see such a star? For a star or even a galaxy, it should only be seen from Earth for a finite time after it has ceased to radiate. The Cosmic Background Radiation seems to be a different situation. What I am about to say assumes that current Big Bang cosmology provides a reasonably accurate description of our universe. When the universe was much less that one million years old, it was an opaque cauldron of elementary particles in a plasma-like state, similar to the state of the atmosphere and/or outer parts of the core of a typical star. The most complex nucleus had at most 3-4 total protons & neutrons. The electrons were not bound to nuclei. This state lasted for several hundred thousand years or less, and the diameter of the universe was perhaps 20 to 1000 light years. I am not sure of the exact details, but they can be found somewhere on the WWW. Somewhere inside that cauldron of high energy particles was the space which was to be occupied by our solar system 7 to 9 billion years later. As the universe expanded, we (and everything else) ended up 12-14 billion light years from that original small universe. That original radiation-dominated universe lasted for much less that a million years 12-14 billion years ago. We still see the Cosmic Background Radiation. That radiation has been traveling at light speed for 12-14 billion years. Has our expansion speed matched light speed? If so, that would explain why we still see the CBR, but raise other questions. I have been pondering this issue using the balloon analogy, which has only helped a little. I wish somebody could come up with a better analogy/description. If you ignore one spatial dimension, you can visualize the universe as the surface of an expanding balloon. When you look at a star 1 billion light years away, you are seeing it as it was 1 billion years ago on the surface of a smaller balloon. The world line of a photon from that star is a curved path in spacetime starting at the star on the smaller balloon and ending up at your eyeball on the surface of the current balloon representing the universe now. I imagine the world line of the Earth to be along a radius vector from that smaller balloon to the current balloon. | I assume that all points 1 billion light years from Earth form a circle on the surface of a smaller balloon corresponding the universe of 1 billion years ago. I further assume that the Earth of one billion years ago was on the surface of that balloon equidistant from each of the points on that circle. We do not see anything from that universe either inside or outside that circle of points. I do not know how good the balloon analogy is. I am not sure about the shape of world lines for the Earth and a photon originating far from Earth. The world line of a photon from the universe of 12-14 billion years ago escapes me. That universe was many orders of magnitude smaller than the current universe. The balloon analogy makes it a tiny sphere at the center of our current sphere. For all I know, the world line of a photon from that universe could be a spiral coming very close to the Earth’s world line more than once (assuming the Earth World line to be along a radius vector). I still do not understand why we can see the cosmic background radiation. If an intelligent species is near to the Earth of 20 billion years from now, will they still see CBR? How about 100 billion years from now? If CBR can still be seen in the far distant future, how do the world lines of current day CBR photons compare with the world line of those future CBR photons? How does the world line of the center of our sun compare with either of those photon world lines? The balloon analogy does not quite hack it for me, and I have never seen anything better. I wonder if anybody has read this entire post.
The CBR come from 300000 years after the BB (when the universe became opaque) The universe had by then expanded exponentially, so much that the original ball is now flat (with a precision of 10^60 decimal places!). So the universe is really, really <b>big</b>. Our visible universe is only a sphere 13.7 light years big (and expanding at the speed of light) ,so it is still uncovering more of the early universe. (the light from a distance of 14 million light years still hasn't reached us, <i>until 0.3 million years has passed</i>) (the light from a distance of 10 million light years <b>has already</b> passed us, <i>3.7 million years ago</i>) Oh, could we still see such a star? no
