Posted on 01/20/2015 4:43:30 PM PST by LibWhacker
Some simple observations about the universe seem to contradict basic physics. Solving these paradoxes could change the way we think about the cosmos
Revolutions in science often come from the study of seemingly unresolvable paradoxes. An intense focus on these paradoxes, and their eventual resolution, is a process that has leads to many important breakthroughs.
So an interesting exercise is to list the paradoxes associated with current ideas in science. It’s just possible that these paradoxes will lead to the next generation of ideas about the universe.
Today, Yurij Baryshev at St Petersburg State University in Russia does just this with modern cosmology. The result is a list of paradoxes associated with well-established ideas and observations about the structure and origin of the universe.
Perhaps the most dramatic, and potentially most important, of these paradoxes comes from the idea that the universe is expanding, one of the great successes of modern cosmology. It is based on a number of different observations.
The first is that other galaxies are all moving away from us. The evidence for this is that light from these galaxies is red-shifted. And the greater the distance, the bigger this red-shift.
Astrophysicists interpret this as evidence that more distant galaxies are travelling away from us more quickly. Indeed, the most recent evidence is that the expansion is accelerating.
What’s curious about this expansion is that space, and the vacuum associated with it, must somehow be created in this process. And yet how this can occur is not at all clear. “The creation of space is a new cosmological phenomenon, which has not been tested yet in physical laboratory,” says Baryshev.
What’s more, there is an energy associated with any given volume of the universe. If that volume increases, the inescapable conclusion is that this energy must increase as well. And yet physicists generally think that energy creation is forbidden.
Baryshev quotes the British cosmologist, Ted Harrison, on this topic: “The conclusion, whether we like it or not, is obvious: energy in the universe is not conserved,” says Harrison.
This is a problem that cosmologists are well aware of. And yet ask them about it and they shuffle their feet and stare at the ground. Clearly, any theorist who can solve this paradox will have a bright future in cosmology.
The nature of the energy associated with the vacuum is another puzzle. This is variously called the zero point energy or the energy of the Planck vacuum and quantum physicists have spent some time attempting to calculate it.
These calculations suggest that the energy density of the vacuum is huge, of the order of 10^94 g/cm^3. This energy, being equivalent to mass, ought to have a gravitational effect on the universe.
Cosmologists have looked for this gravitational effect and calculated its value from their observations (they call it the cosmological constant). These calculations suggest that the energy density of the vacuum is about 10^-29 g/cm3.
Those numbers are difficult to reconcile. Indeed, they differ by 120 orders of magnitude. How and why this discrepancy arises is not known and is the cause of much bemused embarrassment among cosmologists.
Then there is the cosmological red-shift itself, which is another mystery. Physicists often talk about the red-shift as a kind of Doppler effect, like the change in frequency of a police siren as it passes by.
The Doppler effect arises from the relative movement of different objects. But the cosmological red-shift is different because galaxies are stationary in space. Instead, it is space itself that cosmologists think is expanding.
The mathematics that describes these effects is correspondingly different as well, not least because any relative velocity must always be less than the speed of light in conventional physics. And yet the velocity of expanding space can take any value.
Interestingly, the nature of the cosmological red-shift leads to the possibility of observational tests in the next few years. One interesting idea is that the red-shifts of distant objects must increase as they get further away. For a distant quasar, this change may be as much as one centimetre per second per year, something that may be observable with the next generation of extremely large telescopes.
One final paradox is also worth mentioning. This comes from one of the fundamental assumptions behind Einstein’s theory of general relativity—that if you look at the universe on a large enough scale, it must be the same in all directions.
It seems clear that this assumption of homogeneity does not hold on the local scale. Our galaxy is part of a cluster known as the Local Group which is itself part of a bigger supercluster.
This suggests a kind of fractal structure to the universe. In other words, the universe is made up of clusters regardless of the scale at which you look at it.
The problem with this is that it contradicts one of the basic ideas of modern cosmology—the Hubble law. This is the observation that the cosmological red-shift of an object is linearly proportional to its distance from Earth.
It is so profoundly embedded in modern cosmology that most currently accepted theories of universal expansion depend on its linear nature. That’s all okay if the universe is homogeneous (and therefore linear) on the largest scales.
But the evidence is paradoxical. Astrophysicists have measured the linear nature of the Hubble law at distances of a few hundred megaparsecs. And yet the clusters visible on those scales indicate the universe is not homogeneous on the scales.
And so the argument that the Hubble law’s linearity is a result of the homogeneity of the universe (or vice versa) does not stand up to scrutiny. Once again this is an embarrassing failure for modern cosmology.
It is sometimes tempting to think that astrophysicists have cosmology more or less sewn up, that the Big Bang model, and all that it implies, accounts for everything we see in the cosmos.
Not even close. Cosmologists may have successfully papered over the cracks in their theories in a way that keeps scientists happy for the time being. This sense of success is surely an illusion.
And that is how it should be. If scientists really think they are coming close to a final and complete description of reality, then a simple list of paradoxes can do a remarkable job of putting feet firmly back on the ground.
Because Special Relativity only applies to uniform reference frames [including reference frames where an observer is measuring the speed of light] when the motion of an observer relative to what he is observing is no longer uniform, the rules of Special Relativity can be broken.
So if I understand you correctly, if something is moving erratically it can move faster than light, and only if it moves at a constant velocity can it be said that it cannot go faster than light?
That doesn’t seem right. Vigorous enough wiggling could hypothetically allow FTL travel while negating all time dilation.
Two observers separated by large enough distance are not in uniform reference frames with respect to each other.
http://scienceline.ucsb.edu/getkey.php?key=1842
An event horizon can basically be thought of as the boundary of a black hole, although there’s nothing actually there that could be touched or anything like that. What’s special about an event horizon is that once anything, matter or even light, passes beyond the event horizon, it can never escape from the black hole, and will continue falling towards the center of the black hole, which is called a singularity. This is because at that point, the gravitational field of the black hole is so strong that nothing, not even light, can reach the escape velocity necessary to leave the black hole. Because of this, it’s impossible to get any information out of a black hole, so we can’t really know what’s beyond an event horizon.
Warp drives aren’t going to happen, IMHO. I gave reasons why elsewhere on this thread. Wormholes might be more/less likely in a Quantum Theory of Gravity, but I would guess most astrophysicists/cosmologists expect the likelihood to be the same either way.
Remember, the balloon is a 3D visualization of a 4D world [ours.] So we must remove one dimension -- and keep in mind that we removed one dimension -- in order to produce the visualization.
Our world: 3-space, 1-time dimension. Balloon world: 2-space, 1-time dimension. The time dimension in the balloon world is represented by the radius of the balloon. As the balloon expands, the 2 spatial dimensions on the skin of the balloon are evolving in time [moving farther apart.]
That is the answer to your question.
Inside the balloon is the past. "Inside" the 4 dimensional hypersurface of our universe are all of our yesterdays. Outside of the balloon is what it is evolving into: the future. And that is what is "outside" of the four dimensional hypersphere of our universe is our future.
You are correct [as far as we know] that there is a barrier that keeps us from going "outside." And there is also a barrier that keeps us from going "inside" as well. We cannot visualize it, but we know that we cannot travel through time.
That barrier has a name: Entropy.
I appreciate the answer but I'm still unclear about the "barrier".
Are you saying that the "barrier" that would prevent us from viewing or knowing what lies beyond the edge of the universe is "time" in the sense that we would never have enough time in which to actually travel to that edge?
Or is there another explanation that I can't seem to grasp?
What is “outside” is the future. What is “inside” is the past. We are expanding into the former. We are forbidden by Entropy from travelling into the latter.
Everything ahead of us is of course the future. If I wish to travel to northern Michigan for the weekend, that trip would be considered the future until I arrived at my destination then it would be the present.
In applying the same principle to a universe that is expanding due to a gigantic explosion that occurred at point A (the center of the universe) and all the debris flying outwards, assuming I have enough time to do so, I decide to plan a trip to the outermost piece of debris in the universe. While it will certainly take a long time to get there, lets say I do.
Are you saying that once I reach that outermost piece of rock which will then become my present, I can't go any further?
If I am still alive (which of course I am in this narrative) my venture beyond that outermost rock would then comprise my "present" on a journey into the future, just as every day life is.
So, either the universe is forever and ever and ever, OR there are boundary limits that have only been explained theoretically via mathematical equations.....
Warp drives aren’t going to happen, IMHO.
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Does this mean at least for the next 200-500 years or so — it will take 10-100 years to reach the nearest stars.
Much of star treck is set out about between 2250—2300. Do you think that bradbery was wildly optimistic about about how long in the future it will be before intergalactic travel is possible at speeds that are faster than inter generational
Again, in my opinion, and I have written on this thread just why this is so, there will never be intergalactic travel. There is never going to be any means of travelling at speeds greater than the speed of light. It’s not a question of technology. It’s a matter of geometry. The fundamental shape of our spacetime is such that it isn’t possible to exceed the speed of light in vacuum.
This is incorrect. In the analogy, Michigan is on the same geodesic surface that we are on. Michigan does not exist in some future time when you arrive there. It is not unreachable because Entropy bars us from travelling there in the past. It exists already. Is exists in the now. The fact that it will still exist when you get there is a consequence of the fact that in travelling to reach it, you can move along a geodesic curve of spacetime to reach it, because it is travelling into the future along with you. If it did not, it would become unreachable.
Don't switch back and forth between the 2D/1T spacetime of the model and a 3D Earth. That mixes the model and invalidates the analogy.
We cannot visualize a four dimensional universe. But we can visualize a 2D/1T slice of it. In that slice, the radial axis is time. When the galaxies move through their spatial dimensions they are restricted to the surface of the sphere. When the sphere expands, all of space, and all of time are expanding along with them. An astronaut moving between galaxies cannot "jump off the balloon" and into the future. All he can do is stay on the surface of the balloon to travel from one spot to another. As he does so, the balloon, the galaxy he has left, and the galaxy that he is travelling to have all expanded outward in spacetime together.
“This statement is objectively false. There is no requirement that objects in relative motion must be moving slower than the speed of light.”
“Nope. Not true [that any relative velocity must always be less than the speed of light in conventional physics.”
“There is never going to be any means of travelling at speeds greater than the speed of light. It’s not a question of technology. It’s a matter of geometry. The fundamental shape of our spacetime is such that it isn’t possible to exceed the speed of light in vacuum.”
What? These posts of yours quoted above seem self-contradictory. This is why I’m confused. Your latest quote is what I thought was true, but before that you seemed insistent that it was wrong.
Which one is correct?
“Has nothing to do with wiggling.
Two observers separated by large enough distance are not in uniform reference frames with respect to each other.”
According to your earlier post, the Special Theory relies on 2 things: constant velocity and uniform reference frame.
I assumed uniform reference frame with anything we observe. If something can be observed, it is inside the same universe and hence the same physics apply to me as they do to the observed object.
The only other variable was constant velocity. Wiggling negates that, thereby cancelling out the rules applying to the Special Theory, according to the rules you told me.
This assumption is false. With a not very powerful telescope and under the right conditions you can see [for example] GPS satellites in Earth orbit. They are circling the Earth, their velocity vector is turning every moment, and thus they are not in a uniform reference frame with respect to us on the ground. General Relativity, not Special Relativity applies. This is confirmed in practice. Microsecond adjustments must be made to the proper time of the satellites clocks or GPS would be too inaccurate to be usable.
If something can be observed, it is inside the same universe and hence the same physics apply to me as they do to the observed object.
I don't really know what this means. If you mean: under the same physical conditions the same physical laws would obtain, OK... this is the heart of your misunderstanding. Take a local frame of reference which appears not to be moving. All the physics within that small local frame is the same. Take another local frame a billion parsecs away. Within that small local frame, the physics within that small local frame is the same as ours. But that does not mean that we see the same physics going on in his part of the universe that we see in ours. Because of the expansion of space, he is accelerating away from us. When we watch what he does, we do not see what he sees. For example, if he were taking a measurement of the signature lines of sodium atoms, it would appear to us that those lines are being seen at wavelengths that are considerably longer than where we see them. IF we make your assumption, we have to account for the fact that what he is measuring turns out to be the same as what we are measuring, even though the numbers are different. And the conclusion we will arrive at is that his part of the universe is moving away from ours at a significant percentage of the speed of light.
If an object is wiggling, it's subject to the General Theory of Relativity, not the Special Theory of Relativity. The Special Theory doesn't apply to accelerated motion.
Can you "wiggle" faster than the speed of light? No. But there are some dodges. Here are some:
Quantum teleportation: The effect of spin flipping in Bell's Theorem Experiments are apparently propagated faster than the speed of light. This is permitted, because a change in quantum states which conveys no information cannot be used to elsewhere violate causality. I am not going to try to explain why this is true; some of the greatest physicists in history have had serious problems understanding it. But it does very much appear to be true. Google No Communication Theorem if you're interested.
Mathematical entities which are non-material: The "superluminal scissors" or "scissors paradox" is an example that has been known for a long time [You have to be careful how you construct the scissors, as the post at link discusses. But as the "caveat" section makes clear, there is no problem with the vertex point of a pair of closing scissors moving faster than the speed of light.] http://math.ucr.edu/home/baez/physics/Relativity/SR/scissors.html
Our universe. Space is expanding pretty much uniformly in all directions. This means that as objects get further away, their relative velocities are increasing. The further they are, the greater the apparent difference. This gives rise to a Doppler affect red shift. The most distant objects are the most red shifted. The most distant objects are those moving away from us at the greatest speed. Far enough away objects would have apparent velocities which exceed c -- if we could see them. we can't. The wavelengths of light they emit are red-shifted to infinity. Events occurring in those regions can never be detected. We are beyond their event horizon [and vice versa.]
In all three cases, the essential dodge is that no information can be transmitted by the superluminal effect. Thus, there is no Loretntz frame that can be use to violate causality.
The fundamental shape of our spacetime is such that it isn’t possible to exceed the speed of light in vacuum.”
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If our space time vacuum is like the skin of a balloon expanding—then is it is unlikely that our spacetime vacuum is leaving behind a space time vacuum and expanding into a space time vacuum.
While telescopes have been pointed to the galaxies that are furthest away. I have not seen pictures of the direction of space from which the presumably the big bang originated.
I think I’m beginning to understand. Your stated definition of “uniform reference frame” wasn’t the same as what I thought. You stated it’s the same environment. In regards to Special Theory, it’s more like the same relative velocity instead of some sort of surroundings.
Everything else you’ve posted in response is either “General Theory applies, not Special Theory” or giving a hypothetical, unobserved example (i.e. thought-experiment and/or mathematical construct).
Thanks.
By the way, why is it that you no longer teach physics and are now in the concrete world of computers?
Bell's Theorem Experiments are real experiments, not thought experiments, but the scissors paradox is a pure hypothetical. However, both give some insight into how the supposed absolute "nothing can exceed the speed of light" can break down. The apex of the scissors is a physical point, and it can exceed the speed of light.
Why do these examples matter? Well, for the reason you hint at -- when you say "unobserved," which is a good insight -- but not quite true.
The real physical point of "nothing can exceed the speed of light" is this: If there is a Lorentz reference frame in which an object/event propagates information faster than the speed of light, then there is a reference frame in which the event appears to happen before its cause. Causality violations do not appear to happen in our universe.
So, the "loopholes" can be broadly categorized: Events can be connected by apparent FTL propagation provided that no information can be conveyed. That is what has tripped up the author of this article and that is why Bell's Theorem, which has tripped up so many great physicists and nearly all laymen is important in this context. It appears that quantum state flipping occurs "instantly" no matter how far apart the components of an entangled system might be. But there is nothing we can do with the fact, because no information is conveyed.
Same thing actually with the apparent FTL velocity of distant objects in space in a different way. Those objects "apparently" moving FTL because of the expansion of spacetime 1) do not appear to be FTL in their local Lorentz frames and 2) are beyond our event horizon, so they can never be used to violate causality. They are not part of our observable universe.
The answer to your other question is, I loved teaching but was told that nobody in any university would hire me to teach, that I wouldn't be rewarded for teaching, even teaching well, and my research was all computer calculations and simulations. So I decided if I was going to be paid to be a computer jockey I could make a lot more money just being a computer jockey. I miss teaching, but that's about all of the academic world I miss. No regrets.
But you have!
Because of the finite speed of light, when you see a galaxy 14 billion light-years away, you are looking at something that existed 14 billion years ago. You are looking into the past. All of spacetime: both space and time are moving away from the Big Bang. When you look at a galaxy 14 billion years ago, you are looking in the temporal direction of the Big Bang.
Marked
When you look at a galaxy 14 billion years ago, you are looking in the temporal direction of the Big Bang.
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This is very hard to picture because the galaxies that are from 14 billion years ago are also presumably furthest away. I thought that when we see those slow zooms to the most distant galaxies whose light comes to us from 14 billion years ago—that we were also looking at the edge of the universe where galaxies are expanding outward the fastest— so that even though their light comes to us from 14 billion years ago — these galaxies right now are 14 billion light years ahead of us in the direction of the expansion of the universe.
So in effect the origin of the big bang is in the direction of the light or 180 degrees from these distant galaxies as the light passes by the earth and journeys to the place from which the big bang came—or 180 degrees away from these distant galaxies in the opposite direction. That direction is the opposite end of the telescope when its gazing at the galaxies furthest distant.
Now here please correct my understanding.
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