md65536

I think it proves my point, that we know the special theory of relativity in terms of the Lorentz transformation and e=mc^2, rather than say the theory of what it would be like to ride on a wave of light. As Delta1212 points out, the theory implies more than just the examples or experiments that lead to it. I definitely agree it's important to imagine these things, especially as Einstein did with things that have never been thoroughly thought out before, and even when it's nothing new it's still not a waste of time to do so. Sorry to carry the digression further. But to try to bring it back to the topic, it is in theory that light cannot be measured from any meaningful "point of view of light". That all experiments or examples agree with it is what makes a theory accepted.

Not really... I agree it's helpful and interesting. It's like trying out different examples in SR and asking "will this example work too?" It's interesting to see that it does work out, but it's better to realize that SR is consistent and not question whether the examples will work, because until you see why they all will, you can forever question it with more examples. There is no way in which a frame of light has meaning. If you came across one, that would be a problem that would need to be looked at and resolved, but I don't think it's "important" to look for such problems. It's like saying "It's important to think about ways that reality might not be consistent, so that we can make sure that reality is actually consistent!" You can assume that it is, until you have a real problem. Agreed that they're good exercises to think about these things. I agree with your second paragraph. Our measurements of time and distance are defined by light c, and our experience of reality is defined by how we measure it, so it's definitely related to not being able to define measurements in terms of "what light sees". I agree with you pretty much, but just nit-pick on some of the details. I don't think that understanding relativity through examples is the right way to go, unless you can generalize from the examples and make further predictions from it. And that's usually not the case... often people will understand eg. the results twin paradox, but they'll not know why it's so, and so with the next example that comes along they'll have to relearn or be told how it works out. Best I think is to understand it in terms of the theory and the maths, and understand that it is consistent. Then, any new example can be worked out and predicted, and each example only reassures you that it all works out, rather than every new example being a new mystery to puzzle over. In this case, lack of a frame of light comes from math. Any examples of what that means, physically, are consistent with the math. So, unless you can deduce all of the other possible examples from an inability to measure return trips, then the return-trip example is not a sufficient explanation for why light can't have a frame of reference.

No, it is physically meaningless to speak of a frame for light, if you properly deal with all the details of SR (and if you don't, you'll probably derive contradictions). Any way you look at it, such a frame doesn't make sense. Mathematically; or imagining riding on a wave of light; or considering length contraction and time dilation in the limit of v as it approaches c (there's no proper time for light); or considering measurable properties of a photon---no proper treatment will give you a meaningful frame for light. Yes, you could imagine something false by ignoring some details, just like you could imagine anything else that's physically meaningless. Your example---that you couldn't measure c relative to a photon with round-trip timing---is consistent with the principle that the photon doesn't have an observational frame of reference, but it doesn't define it.

Ah, sorry, I got mixed up because "relative to" was used twice maybe to mean different things, each of which you defined, but I took it to mean that the difference of velocities could be defined as "speed in the coordinate system of each other" (but relative to some observer), and now I'm still not sure: Can you define a coordinate system of a photon, relative to another frame of reference? Or is a coordinate system the same as a frame of reference?

Is this true in all frames (that the photons separate at 2c), or does it imply defining the coordinate system relative to the light source's frame? Or does a separation speed of 2c only occur in frames from which the directions of the photons are collinear?

The close-up of the cube gives a tilt-shift effect (the focus along a horizontal line of pixels is the same regardless of the illusive 3d content of the scene). I think the brain accepts it as a camera effect and ignores it rather than trying to process actual depths from the focus. If you pause the video around 0:26 and stare at it blankly, the actual shape of the paper starts coming through a bit, as the depth cues don't match the perceived cube shape. The sides of the cube seem to bend outward toward the top. The top "near" corner seems to be pushed backward. I think it works well on camera because the brain understands and handles camera effects, and doesn't strain to process them. Also, the camera carefully avoids horizontal movement, which would ruin the effect.

I see... you're saying you've done more work with B because you've also lifted the weight of the rope around your waist. But this means that doing some amount of work is equally easy no matter how much time it takes. Bench-pressing 100 lbs once is equally easy as benching 10 lbs 10 times, and pulleys don't make anything easier. I disagree. But even so, you haven't considered that as you approach the rafters, you have 20 feet of rope on one side of the pulley and an amount approaching 0 plus what's tied around your waist on the other side. If the rope was (extremely) heavy enough, you'd reach a point where the weight of the rope itself could pull you up to the top. I think that practically, the weight of the rope doesn't matter.

There are lots of different ways to analyse the twin paradox (see http://math.ucr.edu/.../twin_vase.html), and many different explanations depending on how you set it up. There's the "lack of symmetry with proper acceleration" explanation already given. If you describe the paradox in terms of Doppler effects or regular signals sent between the twins, you'll find that each twin receives the other's signals at a lower rate on the outbound journey and an accelerated rate on the inbound journey, but that the two halves of the journey appear to take equal times for the traveling twin while the Earthbound twin sees the outbound journey appear to take a much longer time than the inbound journey, thus receiving a smaller number of signals from the traveling twin (ie. a lower count of aging). Another explanation is that the changes in inertial frame correspond to changes in simultaneity. So while you might say that both are "measuring" or predicting the other twin aging slower than one's self, the traveling twin's turnaround corresponds to a change in simultaneity that involves the Earthbound twin essentially changing to a much later, much more aged relative simultaneity. This is why I said in post #7 that you must include relativity of simultaneity and not just length contraction and time dilation, because otherwise it's possible to derive false contradictions.

How many feet of rope have you pulled in each case? If with each pull of the rope, you pull 1 foot of rope, how many pulls does it take in case A and B? What is the change in potential energy per pull of the rope in each case? Assuming negligible friction etc, the difficulty could be expressed in terms of the change in potential energy of each pull.

I disagree as I think that would count as being "around".

Well uh, yes and no... Approaching objects take up a reduced portion of your field of view but they also look farther away, giving them the appearance of being stretched. Receding objects cover a greater portion of your field of view but they also look like they're close up, giving the appearance of being compressed. If every circle appears circular then the approaching stretched circle will have to appear stretched in all directions. -- sorta. But like you point out, that doesn't give you a meaningful measure of size. If you place rulers across the circles (at rest relative to them) then the rulers appear to stretch or shrink too, and the diameter of the circle remains fixed relative to that ruler. If you've placed two rulers across the center of an approaching circle, one parallel to your velocity and one perpendicular, then the parallel ruler will appear be perceived to be stretched while the endpoints of the perpendicular one appears to shrink, and yet the circle remains perfectly circular-looking! This is possible because the endpoints of the perpendicular ruler also appears to move forward around the edge of the circle (like the stretched skin we've been talking about) so it no longer appears to bisect the "apparent" circle. Also the perpendicular ruler happens to not appear straight, with its middle appearing to curve toward you. I understand that there's a distinction between how things look and how they are, and I'm mixing it up a little, but I'm still interested in understanding how things look. Anyway, the illusion of approaching objects appearing to stretch away from you really is apparent. Things really do appear to move away. However if you realize that they are also appearing smaller in your field of view then you no longer accept that they are farther away, and then the illusion becomes clearer. Here's a video of the effect, from MIT's recently released relativistic game: Around this point in the video, the player is usually moving forward (and you can see it is so around the edges of the screen), yet the higher the velocity, the farther the center of the view appears to move away. However, if you measured the size of anything in pixels, nothing that "appears stretched" away from you should ever actually take up an increased length in pixels. Also interesting in the video, the spheres that you collect never appear to be distorted by relativistic effects. (Not that this is a perfect measure, especially considering that just by projecting a game-world view angle onto a screen with a different view angle -- depending on how big your screen is and how close you are but typically games have an exaggerated view angle -- the spheres will be distorted by this projection, as they would be also in non-relativistic games, more so toward the edges of the screen). So I suppose you are right, by most measures even the appearance of approaching circles would seem smaller. Except for the illusion by which their smaller appearance makes them seem farther away, and that the brain perceives distant objects as bigger, ... well I guess you might say that approaching objects appear smaller yet are perceived to be bigger. This brings up more questions but I think we've figured out the main thing I was interested in, thanks.

It's funny how it starts with an ability to reason about the existence of unmeasurable things with no possible evidence, and ends with an inability to reason about a non-existence of such things. It's an interesting idea to contemplate, but without any evidence or physical predictions, it's not reasonable to assume the existence of other worlds, and it goes against the basic concepts of science to do so. Certainly, such ideas may predict actual physical things, such as EM waves of such low energy that we could not detect them, but just supposing that something else could detect them doesn't make it reasonable to assume that such somethings must exist. In the end it becomes like all the other ideas of "things that exist but there is no possible evidence of", such as luminous ether, tiny spherical particles filling all of space, parallel universes, etc. When you get there, any idea becomes "reasonable" if there's no way to falsify it. Light is actually carried by tiny invisible gnomes on jet skis, etc.

The gravitational pull of the sun is much greater than the pull of the moon, but because the moon is much closer the gravitational gradient is higher, so the moon causes greater tidal effects. Wouldn't that imply that the Earth would become tidally locked to the moon? I don't suppose it's possible to be tidally locked to both, unless the moon was at a Lagrange point? I suppose that because of the directions the Earth is spinning and the moon is orbiting, simply slowing the Earth's spin would cause the moon to become geosynchronous before the sun would be. At that point the moon would cause no torque on the Earth but the sun would still slow the Earth's spin ever so slightly. Then the moon would appear to "move backwards" slowly through the sky and try to slow the Earth's spin in the opposite direction. Would it eventually stabilize into "mostly locked to the moon, but with a very very slight rotation caused by solar tidal effects? Or would permanent tides cause permanent deformation of the Earth that would keep it locked to the moon forever?

The moon is a hoax! It is just a giant spotlight on top of a pyramid in the dessert in Nevada, beamed onto the reflective crystal surface of the celestial sphere!

I was thinking about the apparent mass distribution of a spherical shell, and whether or not the interior of a massive shell would have a net 0 gravitational force as with Newtonian gravity, but I switched to a point mass as a simpler case to figure out first. If there's no apparent distortion of a gravitational field, then the interior should have no net gravitational force --- or would relativistic mass affect this? Edit: Thinking too much about aberration I forgot about length contraction. Would a sphere behave gravitationally like it was flattened (and closer) in the direction of relative velocity, regardless of how it appears? Mainly I'm considering how aberration preserves the apparent shape of a circle, and considering that this is true for any orientation of a circle relative to a ship's position and velocity. Is it???? Or am I wrong, and it's only the 2-dimensional outline of a sphere that appears circular? A sphere should be distorted in a similar way to this: Imagine you have a rigid glass sphere, and over it is a slippery, stretched rubber skin. You can pull on the skin, stretching it more and pulling it to one side of the sphere (the far side, effectively) but the skin remains spherical. This is what aberration would look like. Also, aberration can cause the size of the sphere to look different, but not the shape. As you move directly away from a sphere, it will appear smaller? Ahead of you it should appear bigger -- stretched in a forward direction??? And inside a sphere, I have no idea. Perhaps the forward-facing and backward-facing aberration scaling effect would be reciprocal, so the sphere appears to be the correct size? I need to find a relativistic 3d modelling program, or make one...

But what does that have to do with gravity? Why is there a gravitational force toward mass, instead of "toward everywhere", if everywhere is expanding uniformly?

I'm trying to reason about the effects of aberration when passing through the center of a spherical shell. Suppose we do this at near c and describe what we see when we pass through the center point of the sphere. Suppose we enter at the south pole heading for the north. - The sphere will appear perfectly spherical. Every great circle inscribed on its surface will appear as a perfect circle (though not all appear the same size). - The south pole will appear much closer than the north. The equator will appear "squished forward", so that the southern hemisphere looks much bigger than the northern. - We experience no aberration of gravity, so if we suppose that the sphere is massless but there is a massive gravitational body at a single point on the equator, then as we pass the center we feel a gravitational pull directly to our side even though we see the mass ahead of us??? Is this correct?

Indeed. And what direction does it predict that gravitational forces should point? It suggests that an expansion is somehow centered on each quantum of mass. This is not what the original idea proposes (a single universal uniform expansion). This goes back to the original problem I see with this. On one hand it predicts nothing -- as you've mentioned if everything expanded while maintaining a constant ratio between any given lengths, there would be no way to know that it happened. And on the other hand it predicts everything (gravity, arrow of time, observations of distant galaxies, all the things you mentioned), which is a contradiction. I still see no concrete predictions (and I haven't imagined any), and with hand waving one could predict one thing as easily as the exact opposite thing. Explaining "more stuff" without any details will only add problems. For example, if gravity is equivalent to cosmic expansion, why would we not see a stronger correlation between expansion and gravitation? If the goal is to find something involving a square of distances, you might end up shoe-horning the idea to force it to fit what you want it to fit. I think a better goal would be to analyse: What are the consequences of the idea? If it happened, what might we see? Then if that doesn't fit what you want, modify the idea and iterate with more analysis, until it fits something or becomes unworkable. As an example of where to start, imagine an observation of some distant object while this expansion is taking place. How is the observation different than if the expansion didn't take place? If there's no difference, is there some other measurement with a difference?

Well okay, this is a start. 3rd: I think that expansion is already predicted to happen across all distances??? It's just that for smaller distances, gravity and other forces overwhelm the expansion, overriding its effects. Very distant objects have more space between them, and the more space the greater the effect of its expansion. 2nd: How do you know that Vitruvian metric expansion is not time-reversible? For example I could say "Throwing a ball explains the arrow of time, because if you reversed time, the ball would keep going forward," mistakenly assuming that motion is not time-reversible just because time itself seems irreversible. 1st: In your diagrams, everything is expanding at a fixed ratio. If gravity is equivalent to the expansion, wouldn't this imply that gravitational force would be a function of distance, but not of mass? I'm not saying the idea has no value, just that the value is in the details. It may be possible to develop the idea until it fits.

Nevertheless, the effects of different physical phenomena will have a net combined effect. For example, expansion and velocity would both cause Doppler effects, resulting in a single red/blue-shift value that can be calculated. The calculation is just a bit more complicated than simple addition. The combination of things is not always modelled by an addition operation. If you add bananas and umbrellas the result will certainly be bananas and umbrellas. You can also add space-time 4-vectors which include units of length and of time, which remain separate after the addition.

Aether hasn't been proven to not exist; it's been proven to not be necessary. My take on your theory is that it is meant as a simpler explanation for something that mainstream science already explains. Unfortunately, your theory doesn't explain anything. Like aether, it is unnecessary. Also like aether, there is no evidence for it. If it doesn't provide an alternative explanation for any of what mainstream science has, then it can't replace any of mainstream science, and if it adds nothing useful and new, then it is irrelevant. I've tried to imagine how what you propose could explain observed redshifts, or what it means for predictions of the early universe, and I can't draw any concrete conclusions about it. That's where you can step in and defend your theory. What effects would be detectable if your theory is correct, and what predictions are a consequence of it, and how well do those predictions match observed evidence? It's just a forum so I don't think it has to be rigorous and exhaustive, but I think something at least specific is expected. Yes, it could explain everything, just like half of the theories in Speculations can. But does it? Vague descriptions of connections between things fall under what is known as hand waving.

You should be able to use velocity composition and Doppler calculations to get something meaningful, if you're careful. A simple straightforward addition is probably not meaningful. Off topic, but yes.

Well it sounds to me like an alternative to cosmic expansion that "makes more sense to you", but unfortunately doesn't seem to explain any of the observations that we're seeing. Eg. how does redshifting fit in? How does the Big Bang fit in, or what is the alternative? It seems to me, expansion and inflation that are not like you describe here, would still be needed to explain those things. Then, what does this idea explain or improve on where the existing theories are deficient?

If it's possible to detect that this has happened, does that mean that we'd be able to tell that lengths (or rulers) in the past were smaller than they are now, and also that the speed of light in the past was c when measured using local (in the past) rulers? So then the speed of light in the past, if measured using one of our current rulers, would be less than c? What observations or evidence would support this? Is this meant to explain inflation as well? Does this imply that if a light signal is measured to be 13 billion years old, it is from an object that was 13 B light-years away, and that "expanded" 13 B light-years was always 13 B light-years (though according to smaller rulers in the past)?

In your quotes from the paper they say "This observational data rules out linear coasting cosmology", but then they conclude that it can't be ruled out? Are the observational data invalidated?