Question regarding relativity and "infinite" speed - WTF?!

[W.D.Clinger]

Welcome to the forum.

I have highlighted some phrases that, in my opinion, were unnecessarily misleading.

Traveling faster than the speed of light is not mathematically possible -- not without changing the structure of the entire universe. It is the locally minkowsky structure of space time that makes this not only impossible but nonsensical. Non-physicists think of this as some kind speed limit but it is nothing of the kind. You can go anywhere you like as fast as you like -- it has nothing to do with a speed limitations at all. Traveling near the speed of light warps space to shorten the distance to your destination. That is why you can go anywhere as fast as you like. There is even a measure of speed in special relativity that could be called "warp speed" and it represent the real speed with which you can go places --the lorentz contraction factor gamma.

gamma = 1/square root of ( 1 - v^2/c^2) where v is the usual velocity and c is the speed of light

Travelling at gamma = 10 would very much like traveling 10 times the speed of light as far as getting to your destination is concerned. Your velocity (according to the usual definition) is only about 99.5% of the speed of light and that is how fast you would see your destination approach you. But traveling at that speed warps space-time itself so that your distance is only 1/10 of what it was when you were not traveling at that speed. So at that speed you would travel 10 light years in only slightly more than one year.

When you say that high-speed travel "warps space-time itself", what you really mean is that it changes someone's point of view, and that this change in viewpoint results in a different description of time and space, hence velocity and speed. The space-time manifold is not affected at all, which is why I think your explanation is misleading.

Your talk of "real speed" is also misleading, because it suggests some privileged point of view that's somehow more correct than other points of view.

Finally, your explanation isn't even clear about whose point of view is being described. Is it the traveller's point of view? Or is it the point of view of some observer with respect to whom the traveller is moving at a high rate of speed? You seem to go back and forth on that.

I'm not saying your explanation is wrong, once your audience is taken into account. I'm suggesting that your explanation is unnecessarily misleading, even when your audience is taken into account.

 

[gnome]

Does Lorenz contraction cause physical (Newtonian, if you will) compression issues? My gut says no, but another part of me says "why not?"

 

[Vorpal]

Does Lorenz contraction cause physical (Newtonian, if you will) compression issues? My gut says no, but another part of me says "why not?"

The question is unclear to me. There's a pretty literal sense in which the Lorentz transformation is simply a 'perspective change' on events in spacetime. On the other hand, if you are in an inertial frame and you accelerate the ends of rod with the same acceleration, it will experience tension. Maybe a more specific situation would help illustrate what you have in mind.

 

[sol invictus]

Does Lorenz contraction cause physical (Newtonian, if you will) compression issues? My gut says no, but another part of me says "why not?"

I think you probably want to know whether an object in uniform motion at a speed close to c experiences any internal stresses as a result of Lorentz contraction - like whether a brittle china plate would shatter since it's "squeezed" along one axis?

Assuming we get the plate up to speed very carefully (i.e. ignoring the forces that accelerate it), the answer is no. We know that because the basic postulate of special relativity is that the laws of physics are the same in all inertial reference frames. In the rest frame of the plate, there's no Lorentz contraction and the plate obviously doesn't experience any stress that could make it shatter - and therefore the same conclusion (it doesn't shatter) holds in all other reference frames too.

 

[mitchellmckain]

When you say that high-speed travel "warps space-time itself", what you really mean is that it changes someone's point of view, and that this change in viewpoint results in a different description of time and space, hence velocity and speed.

I know that your version is the textbook dogma but it is misleading. The change that is being talked about is really just a change in how the physicist calculates things when he calculates them according to his own inertial frame. To accurately talk about perspectives and thus about what the traveler actually sees you have to take into account the aberration of light (which is something my simulator does), and the result is so counter-intuitive that most people are very surprised when they learn it.

I agree that saying that it warps space-time is technically wrong, but I just don't see a way around it when explaining this in such simple terms and so would would prefer to add such a comment as yours as a caveat at a later time.

Your talk of "real speed" is also misleading, because it suggests some privileged point of view that's somehow more correct than other points of view.

Yes in physics we learn to be able to see things from many different perspectives in the different inertial frames and that is a very useful tool, but for most people when they talk about speed all they really care about is how quickly they get to their destination. In the language of physics, where words have precise mathematical definitions, we really do need to invent a new word for this like "celerity", but for most people introducing a new word like that would only add to the confusion not clear it up.

 

[Vorpal]

I know that your version is the textbook dogma but it is misleading. The change that is being talked about is really just a change in how the physicist calculates things when he calculates them according to his own inertial frame. To accurately talk about perspectives and thus about what the traveler actually sees you have to take into account the aberration of light (which is something my simulator does), and the result is so counter-intuitive that most people are very surprised when they learn it.

What are you talking about? Just about every textbook on relativity makes the distinction between what is seen and what is observed, and yet you're acting like you making this distinction is somehow against "dogma". Clinger is obviously talking about what's observed.

[Edit]: I'm sorry, but the sin of using the word 'perspective' is actually mine, rather than Clinger's. I guess I should have avoided the visual language here, but what's going on is that velocity in spacetime is a direction, and changing is very analogous to changing one's orientation in space, time measurements to depth, and so forth.

 

[phunk]

And if you travel 100,000 light years while only experiencing one second, that's a bit difficult to understand if you've been told that nothing can ever travel faster than light, no?

But the only way to think you've traveled 100kly in 1s is to mix frames of reference, making the measurements meaningless.

If you're going to use the distance from the frame of reference of your point of origin, you should use the time from that same frame of reference also, and accept that it took 100000+ years, whether or not you "experienced" that much time personally.

If you're going to use the time from your own frame of reference, then you the journey was at most 1 light-second long.

This is the whole point of relativity. There is no such thing as absolute time or distance, both are relative. You will never get the right answers if you arbitrarily mix measurements from different frames of reference.

 

[epepke]

Does Lorenz contraction cause physical (Newtonian, if you will) compression issues? My gut says no, but another part of me says "why not?"

I think that everybody who studies relativity grapples with this.

According to relativity, though, there is no absolute. The measurements are the reality, and all the realities are consistent. One could say that it only changes the measurement, but that's a meaningless thing to say, because the measurement is all there is.

 

[W.D.Clinger]

I know that your version is the textbook dogma but it is misleading. The change that is being talked about is really just a change in how the physicist calculates things when he calculates them according to his own inertial frame. To accurately talk about perspectives and thus about what the traveler actually sees you have to take into account the aberration of light (which is something my simulator does), and the result is so counter-intuitive that most people are very surprised when they learn it.

As Vorpal noted, you're accusing me of making a mistake I did not make. I am not concerned with what the traveller "sees", so aberration of light is irrelevant.

BTW, I'm not a physicist. My background (from long ago, so I'm rusty) is in mathematics. I look upon Minkowski spacetime as a geometric object: the simplest 4-dimensional pseudo-Riemannian manifold with Lorentz signature. To describe events in that manifold, we can choose any charts we like from the complete atlas. We can describe the same events using two or more different charts. The Lorentz and Poincaré transformations tell us how to transform one of those descriptions into another.

Yes, that's the textbook dogma. No, it's not misleading.

I agree that saying that it warps space-time is technically wrong, but I just don't see a way around it when explaining this in such simple terms and so would would prefer to add such a comment as yours as a caveat at a later time.

In another thread, Olowkow recommended Relativity for the Questioning Mind, an online book by Daniel F Styer, who's a professor of physics at Oberlin College. From what I've read of that book, it manages to be rigorous without being technical or misleading.

Chapter 2 covers "Space, Time, and Motion". I'd recommend its terminology. Yes, its terminology is standard: That's a good thing, not a bad thing.

The book uses Galilean relativity as an introduction to Einsteinian relativity. In chapter 3, the constant speed of light in vacuo motivates a revision to the Galilean formula for addition of velocities. That, too, is standard. You may think it's boring, but laymen think it's plenty weird. Once again, being standard is not a bad thing.

It's okay to use nonstandard explanations if they're as good as or better than the standard explanations. I don't think your explanation met that test.

 

[gnome]

I'll just add that people trying to answer my question have indeed understood what I was getting at.

 

[MattusMaximus]

I see that Mitch is back and he's talking about the "dogmatic" approach to relativity with which he appears to disagree. Over at the Christian and Atheist forum, where all of this started, when I brought up some of the same criticisms that others here have broached (though I did not express them so clearly), such as disregard for the concept of a frame of reference and why this was confusing, one thing Mitch came back at me with was this "dogma" talk.

I wish I had done something then, but I didn't think of it until now, so I'll give Mitch the benefit of the doubt and ask him this question:

Mitch, could you please outline just why it is that you dislike the "dogmatic" approach that is standard in relativity (as mentioned upthread by W.D. Clinger)? Please try to outline what is wrong in terms of the physics.

And while you're at it, could you also explain why it is that you believe your approach is better? I and others here have already stated why we think it leads to misconceptions, so would you please address those specific criticisms in your defense as well? Again, I readily admit that many others here have voiced these objections far better than I did over at the C&A forums, but I think the criticisms still stand.

Thanks in advance.

 

[mitchellmckain]

There is NOTHING wrong with the way it is taught in the textbooks. What is wrong is in intolerance of any variation from the way in which you may have been taught something. That is when something becomes dogma. That intolerance does indeed have my complete comtempt and I have absolutely no interest in indulging it. So I refuse to discuss criticisms of that sort. I will explain things the way that I decide is best and if you don't like you can lump it. What matters in science are the prediction of measurable results. That is where the science is and unless criticisms are on that basis, it is just hot air. That is why the only real issue in the discussion with Maximus that had any substance was when he declared that I was wrong and said

The fact of the matter is that you can't go anywhere as fast as you like.

So I replied
You give me a time period and a distance and I will tell you how fast you need to go and what energy it will take.

He was wrong and that is the end of the matter. The rest is nothing but hot air. I am just not interested.

 

[MRC_Hans]

Have to say, I'm very much with Mitch here. As already noted, no simplification is going to be perfect, but I don't see anything particularly bad about what he's saying.*snip*

Nothing he's said (at least, nothing that's been quoted here) is in any wrong, and it doesn't even look particularly sloppy to me. *snip*

But other than that really quite minor correction, I don't see what the fuss is about.

I don't see much fuss, but the point, as I already mentioned, is that Mitch's simplified explanations are still shrouded in complex language, so instead if helping the peasants (no arrogance really intended), he may confuse them, and at the same time, more knowledgeable people will expect a precise explanation, and find faults with the simplification.

The simple explanation, and one we have all seen and accepted, can be made like this: "You cannot travel faster than light, but since time will run slower for you as you approach the speed of light, it can seem to you that you are moving faster."

It is important to realize, however, that most people will not imagine themselves as the traveller, but as the observer. So for them c remains a very real and unsurpassable limit.

----

At any rate, I welcome this discussion, simply because it has served to lure Mitch to sign up and participate here. Welcome again, Mitch; you are obviously a very knowledgeable person with an excellent capacity for debate, and I am sure you will be a great asset for our little community.

(Don't mind the bickering, that is part of the game )

Hans

 

[JJM 777]

Time dilation means that the last of the option that you listed does occur. [travelling into the future of OTHERS] Again this is a measured and established fact both in particle physics and orbital measurements.
(...)
I think that there really is an arrow of time [time always moves forward from past towards future, never backwards] and so my answer is no.
(...)
I think that anything that implies time travel should be considered a logical impossibility.

Thanks Mitch, these thoughts coincide with mine.

 

[mitchellmckain]

I don't see much fuss, but the point, as I already mentioned, is that Mitch's simplified explanations are still shrouded in complex language, so instead if helping the peasants (no arrogance really intended), he may confuse them, and at the same time, more knowledgeable people will expect a precise explanation, and find faults with the simplification.

Point taken. On the other hand, perhaps my use of such complex language can be taken as invitation to the reader to ask question about them -- providing me the pretext to talk about them.

It is important to realize, however, that most people will not imagine themselves as the traveller, but as the observer. So for them c remains a very real and unsurpassable limit.

And this is where I disagree. When we are dealing with scientists, yes, but when we are talking about non-scientsts I think the answer is no. This is why I have encountered so many people/student who tell me that "they don't believe in relativity" and in talking to them I quick realize that it precisely because they most certainly do imagine themselves as the traveler and thus think that relativity is saying that the speed of light is some kind of barrier in that sense.

At any rate, I welcome this discussion, simply because it has served to lure Mitch to sign up and participate here. Welcome again, Mitch; you are obviously a very knowledgeable person with an excellent capacity for debate, and I am sure you will be a great asset for our little community.

I don't know. I am already engaged elsewhere at this time. I have been over at C&A for a very long time and I am still not sure that I have learned all the lessons I need to learn there. Perhaps when I have I can be better participant over here. But we shall see what grabs my interest here. Lets take it one thread at a time.

 

[mitchellmckain]

What are you talking about? Just about every textbook on relativity makes the distinction between what is seen and what is observed, and yet you're acting like you making this distinction is somehow against "dogma". Clinger is obviously talking about what's observed.

[Edit]: I'm sorry, but the sin of using the word 'perspective' is actually mine, rather than Clinger's. I guess I should have avoided the visual language here, but what's going on is that velocity in spacetime is a direction, and changing is very analogous to changing one's orientation in space, time measurements to depth, and so forth.

I was thinking that if we were going to do all this nitpicking that it ought to be pointed out that the change being talked about was not what the traveler sees but what he calculates.

BUT I MUST confess that I like your explantion better. A change of orientation is a very good way of putting it indeed.

 

[MRC_Hans]

I don't know. I am already engaged elsewhere at this time. I have been over at C&A for a very long time and I am still not sure that I have learned all the lessons I need to learn there. Perhaps when I have I can be better participant over here. But we shall see what grabs my interest here. Lets take it one thread at a time.

No worries mate! I can recognise a passionate brawler when I see him. You'll come back.



Hans

 

[JJM 777]

Time dilation means that the last of the option that you listed does occur. [travelling into the future of OTHERS] Again this is a measured and established fact both in particle physics and orbital measurements.
(...)
I think that there really is an arrow of time [time always moves forward from past towards future, never backwards] and so my answer is no.
(...)
I think that anything that implies time travel should be considered a logical impossibility.

One more question about this:

Is this understanding of reality based on (or does it result in) these conclusions:
- the amount of matter in universe is finite (or if expanding, only at its remotest outer edges)
- each piece of matter exists exclusively in one timespace (time and location) only, which makes it impossible to travel into a future where you would meet the future you, for example

 

[dasmiller]

What is wrong is in intolerance of any variation from the way in which you may have been taught something. That is when something becomes dogma. That intolerance does indeed have my complete comtempt and I have absolutely no interest in indulging it. So I refuse to discuss criticisms of that sort. I will explain things the way that I decide is best and if you don't like you can lump it.

IOW, you won't tolerate any criticism of your criticism of intolerance?

 

[mitchellmckain]

One more question about this:

Is this understanding of reality based on (or does it result in) these conclusions:
- the amount of matter in universe is finite (or if expanding, only at its remotest outer edges)

I don't see how this is assumed or implied and I believe that what you have in parentheses has been established to be incorrect.

- each piece of matter exists exclusively in one timespace (time and location) only, which makes it impossible to travel into a future where you would meet the future you, for example

Yes I think this is assumed and must be for my conclusions-- at least to the degree that matter can be treated as discrete pieces anyway. If we are talking about quantum sized objects then this would have to be handled a bit differently -- then it is an issue of the transmission of information rather than the location of discrete objects.

IOW, you won't tolerate any criticism of your criticism of intolerance?

Thats done it. Now I'm going to have to send my pet goblins out to skewer you.