Schneibster

No, actually they're defined by the speed of light, which is a constant for all observers in all frames.

Lizzie, if you go down all the tracks what you're going to find is that spacetime is a postulate of relativity. And that space and time are postulates of Galilean and Newtonian physics, as well as Aristotelian. The reason you keep getting stuck on time is because you learned Newtonian physics, not relativity. Special relativity shows the shape of time. In mathematics terms, you're endlessly repeating, "but you haven't defined zero!!!" That mathematical link shows both time's essential sameness to space, as well as the difference in its relations to space dimensions from the way they relate to one another. This is as much of "the character of dimension" as we know. A transform doesn't link two things that are different. It can't. You can't define a transform that turns time into water, or love into electricity. You can define a transform that turns time into space, and vice versa. And it really works that way. So in fact, your claim the transforms don't prove anything is wrong. They do prove something: time and space are, essentially, the same. So, you can actually see space. OK, well, time is no different. It's only difference is in its relation to space. To another time dimension, as uncool pointed out, it appears right circular, just as the space dimensions all appear to one another. It's only when we start having rotations-- in the case of time, that means velocities, or rapidities-- that we have to transform things from time into space, and vice versa, this way. In fact, those transforms are pretty much the most information we have about time and space themselves.

But that doesn't mean they behave the same. They may be the same basically, but their relations to one another are what determines how we see them. When we transform them, we don't actually change any basic quantities.

No. It's about the shape of time relative to space, as shown by the hyperbolic trig version of the Lorentz transform. This is based on the math, Lizzie. Do you not believe the math? Because there's no questioning it. This is basic relativity math. Not even any scary integrals. Just hyperbolic trig. t → (cosh s)t + (sinh s)x x → (sinh s)t + (cosh s)x y → y z → z Or, if you prefer, t → √(1 - (v2/c2)) * (t - vx)/c2 x → √(1 - (v2/c2)) * (x - vt) y → y z → z they are equal. BTW, see that c2 in the t transform? Remember I said we're moving forward in time at the speed of light? There's the mathematical proof. One last point: the traditional light cone is at precisely 45 degrees, and the units are c=1. Making 3d pictures misses the point; it should be t on the vertical axis and x on the horizontal, to make a Feynman diagram. The angle is 45 degrees because in the traditional Feynman diagram the speed of light and the speed of time are equal.

The actual word was "outmoded." Do you need a link?

I missed this cool fact and would like to go back and highlight it because it's cool. It's the relation between a dimension and space dimensions that makes it a time dimension, not the character of the dimension itself. A dimension is just a dimension. It's its relations to the space dimensions that make it temporal or spatial (and if string theory is right there are some other states too).

Weird, it should be on. I'll check on the instructions for FF. Maybe I inadvertently turned it off. Thanks for the confirmation. It says it's turned on: https://support.mozilla.org/en-US/kb/how-do-i-use-firefox-spell-checker Tihs izs alll mispeled and none of it shows up. I have the default editor, with "My Media" in the middle of the top toolbar, and a twitter button in the middle of the bottom toolbar. Any suggestions? I'm toggling it and restarting FF; I'll report innaminnit. Testing, tsetning, testing. Nope. BRB, lemme see if it's working on Foreign Policy and Daily Banter. Could it be a FF bug? I updated today... but I think I remember it further back than that. Hang loose... No, it's definitely firefox. My spell checking doesn't work on other sites either. I'll post a solution when I find it out. I bet it's a firefox bug. Testing aragain and it's stil notwerking. All right, got it. This is way weird: the right-click menu in this text box had "English" unchecked under languages for some reason. Spell check as you type was on in the Options->Advanced->General, and "Check Spelling" was checked in the right-click menu for the text box, but apparently it didn't have any dictionary selected! I suspect a recent update toggled the setting. Or else I had a nervous twitch at just the wrong moment and didn't notice it.

There are multiple specializations within it; I'd include not only solid state physics and condensed matter physics but also exotic matter physics and nanotechnology and materials science. Quantum dots. Nanoarrays that can do unusual optical tasks. BECs. Cloaks of invisibility. Not, for example, developments in string theory. Not relativity. Not high energy particle physics. Not cosmology. Matter physics, mostly solid matter physics. And if there aren't enough articles there will be. Or should be, on a physics forum. Yes, but beyond that. All sorts of unusual or exotic matter, BECs, superconductors, nanoarrays, quantum dots, and so forth.

We completely agree. OTOH, the kernel idea of "one in 137" stuck with me, and I think it gives a good "feel" for how alpha works. And that's really the important part of the analogy for me. And what might be important, I don't deny that later papers may overthrow reality as told in earlier textbooks; but in both cases, I also agree that real evidence must be the determining factor, not authority. I only cite authorities within their expertise and I think everyone else should stick to that too: if you haven't read it don't cite it.

Well I sure as heck won't argue with you about it; I don't share your opinion but I probably like different soy sauce on my sushi from you and I don't intend to argue about that either. I've been telling people, gently, that I think it's a matter of taste and I see no point in arguing about pedagogic techniques, repeatedly. It doesn't seem to be getting through very well. Perhaps they'll listen if you tell them. And just to be picky, since we're being picky, actually I thought his analogy was weak too and tried to improve on it some. So I'm really not disagreeing with you.

And BTW let's also keep in mind that none of the relativity is. The three significant experiments have been Planck, Gravity Probe B, and LIGO/VIRGO in that time. I think so too but I need to be getting across that I gave fair warning it was an analogy in plain language and was then abused because it's only an analogy. I'm becoming irritable about it. I don't understand why staff is permitting it.

It's not just a general foam of equally-sized bubbles, in fact it's got voids (bubbles) of every size from galaxy cluster on up well past the largest matter structures. The distribution appears to be fractal, that is, of similar density at many scales on the largest scales. The assumptions of homogeneity and isotropy have been challenged by COBE, then more strongly by WMAP, and are now being overthrown by Planck. Planck sees a huge "cold spot" in the CMBR. Does that sound like it might be a reverse density fluctuation from the formation of a cosmic void to you? Meanwhile, where did all the matter in the voids go? And the answer is, into the "web" of matter and dark matter and extremely high temperature gas that makes up the galaxy clusters, and out of the voids. And that's why there's voids. Maybe they're where universes with bad cosmological constant values formed. They collapsed back into black holes, or went the other way and blew all their matter out into the surrounding space too fast. Maybe our little matter "salient" between two giant voids is the remains of whatever was in them before they exploded. If they exploded. We're not actually in a universe, we're in the detritus of universes that blew up around us. Just an accident. The Schneibsteress has christened this the "brown universe theory."

They look pretty exact to me. Do you have another interpretation?

Are you talking about voids?

No, I have no major objection. Next time ask me what I think instead of telling me, please.

Well, there was. Whether it's still there is an open question; they're still expanding, because space is, but I haven't seen any research on whether it's at a different rate than everything else is expanding today. Remember that the far side of the largest one is far beyond the post-Big Bang horizon of the universe. We will never be able to see it. The near side is ten billion light years away, or rather was ten billion years ago; it's quite a bit farther by now and accelerating all the time. Pretty soon we won't be able to see the near side of it either. There's no more something "pushing them out" then there is in a foam of soap bubbles, after the source stops pumping stuff out.

Look, I really told the truth here. And you're really being irritating about it. Do you have some physics to talk about?

http://casa.colorado.edu/~ajsh/sr/postulate.html This is not the first time I have posted this here. It's also in post 102. There are four: 1. The spacetime continuum. 2. The existence of globally inertial frames. 3. The measured constancy of the speed of light. 4. The principle of special relativity, "The results of physics experiments are the same in all inertial frames."

Hey, I made a quote that actually supported what I said. Maybe you forgot. Argue as you like with Susskind's pedagogic technique, accusing him of being technically inaccurate in that quote, and especially, damning the whole thing based on it, is completely missing the point, and quite deliberately disingenuously so IMNVHO. I didn't see anything strawman about it. What I saw was a bunch of people saying it wasn't technically accurate after I'd said so in post number four of this thread. Do you deny I said that? Do you deny I meant it? And if no to both, then how is it a strawman? Please explain. Do you mean everyone was making strawman arguments about what I said? Yes, that was true. Still is. Like you are right here. Please don't do that. I still can't believe someone claims Gravitation is a "popular science book." Let me get over that before I start on the whole "obsolete" or "outmoded" thing, which I will start by noting how many printings they've had to go back for because more people wanted it.

Yep. That's the derivation of the Lorentz transform. It's a postulate of relativity. This is one of the Four Big Assumptions relativity is based on. "Space and time form a four dimensional continuum." It's called "The Continuum Postulate."

See, I see this as a strawman. Where did I claim the later, speculative parts of this book were all the rigidly correct word of Teh Dudez Who Know and I wouldn't tolerate any deviance? This is silliness.

To be precise 2.997925x108 m. (Unless someone did a better measurement of c since my admittedly old reference.) Mmmm, maybe- but that appears to be a matter of taste. Actually it seems quite important in defining how a function works to push it around with extreme values and see what it does, to me.

Actually, since you can convert time and space into each other, it's obvious that when a second of time is converted into space, it's a light-second long. There's a mirror assertion that goes the other way, too, that a light-second must be equivalent to a second of time.

It's all the definition we have; it's a postulate of relativity: the spacetime continuum. [math]x \to {x^2}[/math] BTW does not require or define a spacetime continuum. Surely you didn't intend to claim it does. http://casa.colorado.edu/~ajsh/sr/postulate.html Not only that but you do realize that you just substituted x for x, y, z, and t, right? Geometry no workie like that. Light seconds. And that's amusing, but it's not a joke. We are hurtling through time at an unstoppable rate of the speed of light, and we can't ever stop it, we can only slow it down relative to the rest of the universe at best. And that's only by going as fast as we can.

Sure, absolutely. It's time's relation to x y and z that's hyperbolic; considered in itself it's just a dimension, as we see when x and t interconvert to one another. It's the result of that relation that makes us "see" time as "different." Actually, though, it's just a dimension and we expect that there are ten others that have equally important relations. For starters I just say "time is hyperbolic." That's close enough for most people. The ones who want the math, well, now we want to understand it has to be the relation because time can only make a hyperboloid of revolution in association with another dimension, and as we all know from conic sections that means it has two branches. So you are of course correct.