Tachyons travel backward in time?

[JesseM]

Explain mine! How on Earth do you justify yours, with different rules of physics in differ frames!

There are no different "rules of physics", just different answers to frame-dependent questions like "what is the velocity of this object" or "are these two events simultaneous".

Just try to find a reputable resource that defines simultaneity as you do. There are perceived observations of simultaneous spacelike separated events relative to a specific frame only .

What does that mean exactly? Are you saying the events "really are" simultaneous, but different frames have different perceived observations of these events? Or are you saying that different frames have different opinions about whether they are simultaneous, and that there is no single objective truth about whether or not they "really are" simultaneous? If the former, then you're suggesting there is such a thing as absolute simultaneity, which is forbidden by relativity. And if the latter, then how is that different from "talking about simultaneity relative to specific frames"?

But there is no such thing as “talking about simultaneity relative to a specific frame only ”.

Sure there is. In Einstein's thought-experiment with the trains, you can talk about simultaneity relative to the frame of the train, or you can talk about simultaneity relative to the frame of the embankment, just as Einstein himself did. (I note you continually ignore these quotes I posted--perhaps you realize they undermine your position?) Both ways of talking are equally valid. You can't talk about simultaneity without specifying which frame you're referring to, though--that's what I meant by "simultaneity relative to a specific frame".

Are you dense? Did you read what I said simultaneity means. The only way to declare spacelike separated events as “actually simultaneous” is to make assumptions outside those allowed by SR & the principle of simultaneity. I was very clear on that!

Yes, and it seemed like you were saying that in astrophysics, physicists do make assumptions outside of the SR notion of simultaneity, so that astrophysicists can decide whether events are "actually simultaneous". If you did mean this then you're totally wrong, simultaneity is still relative in astrophysics. If you didn't mean this, then please explain what you were talking about when you said:

You guys seem to think “simultaneity” says something like “you may consider same time events within a common frame to be simultaneous”! Or as you put it “that simultaneity is relative to your choice of reference frame”!
That could not be more wrong, SR says nothing of the sort nor is it a part of “the way the Lorentz transform works”. Simultaneity applies uniformly the same in any frame of reference as any physics rule should. It says that those observers in order to truly understand the reality of their own reference frame must recognize that spacelike separated common time events cannot automatically be considered simultaneous! Additional, SR cannot and is not the tool to establish any two spacelike separated as being simultaneous.

Dang, that makes it hard to use, how can astrophysicists get any work done!
They make an assumption!
A non SR, let's ignore Simultaneity for a special case inside a few thousands of light-years around ( more if we can get by with it). You cannot call such a departure from SR “relativity” and they don’t – it’s called Astrophysics as they presume to establish a preferred reference for at least a local region of space (but often much larger) based on the CMBR. (Particale Physics doesn’t need or use such a device AFAIK)

And more than simultaneous it also includes declaring you can tell from inside a single reference frame if an event happened before or after some other space like separated event Which is exactly what you did!

You seem to be accusing me of saying that "from inside a single reference frame" I can determine some objective truth about whether one spacelike separated event happened before or after another one. But I'm saying the opposite, there is no objective truth about which of two spacelike separated events happened before the other one, this question is frame-dependent just like the question of which of two objects has a higher velocity than another one (from the perspective of either object's rest frame, it is the other object that has a higher velocity, and both frames are equally valid). Do you disagree? Do you think there is a single objective truth about which of two spacelike separated events happened before the other one?

And I are you really so dense as to not recognize you used two different preferred frames to do it!

I used zero preferred frames, silly. I just talked about the judgment of simultaneity in each frame--just like Einstein and other physicists did in the quotes I gave you--but I didn't say either frame's judgments were to be preferred over any other's. This is no different than talking about the judgment of some object's velocity in different frames, naturally the different frames disagree about the object's velocity, but none is preferred so there is no single objective truth about its "real" velocity.

Some of the most ignorant comments I’ve ever seen. Is there any clearer evidence that you are using a preferred frame when you declare “In the unprimed frame these events are simultaneous”!

Do you think Einstein is using a preferred frame when he says "Are two events (e.g. the two strokes of lightning A and B) which are simultaneous with reference to the railway embankment also simultaneous relatively to the train?" Do you think Taylor and Wheeler are using a preferred frame when they say "For the situation described above, the two events are simultaneous as measured in the Earth frame; they are not simultaneous as measured in the train frame." I guess everyone in the world is ignorant of the correct way to talk about simultaneity except for you, Randall?

Again, simultaneity is clear you cannot say those events “are simultaneous”, you can only say that they appear to be simultaneous only from within the frame.

WHICH IS EXACTLY WHAT I SAID! Seriously, what are you smoking here Randall? I have always said that events are simultaneous only relative to a particular frame (for example, that's what I was saying in the statement you just said was wrong, namely 'In the unprimed frame these events are simultaneous'), are you totally lacking in reading comprehension?

If you two are able to convince others that your “backward time” assumptions can be supported by “Einstein Simultaneity” so much the worse for the credibility of these forums.

It can only be supported in the case where it is possible to send signals faster than light. If you think it's not widely agreed upon that faster than light signals + relativity = backwards in time signals, take a look at http://books.google.com/books?id=kHpaBsicVTkC&pg=PA218&dq=tachyons+causality&lr=&sig=fTBj7bP6GW5CpLzxYhxnY7_O-2E section of a popular book by theoretical astrophysicist http://www.edge.org/3rd_culture/bios/rees.html, or the bottom of p. 236 of this introductory relativity textbook, or this section on tachyons from the entry on 'backwards causality' from the Stanford Encyclopedia of Philosophy. This is quite standard stuff.

 

[Dale]

Why not start your explaining with the one you left out, simultaneity.

I didn't leave it out, it is in the text you quoted above. And I already defined it in post 57 which you quoted in post 59. For clarity:

Simultaneity: two events are called simultaneous if they share the same time coordinate.

Relativity of simultaneity: as a consequence of the Lorentz transform, two events which are simultaneous in one inertial reference frame may not be simultaneous in another inertial reference frame.

In other words Sir Spam, put up or shut up.

Grow up Randall.