Frames Colliding - a question

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I wonder how either observer (a) or Observer (b) can know they are about to collide if both considers themselves at rest. [Am I missing something here]

I am sure this is not a new question and I am interested in how SRT deals with it.

Care to discuss....

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From a's perspective b is approaching from the right.

From b's perspective a is approaching from the left.

From either perspective, c will appear to be receding to the rear, at some angle.

This is the most important thing that seems so hard in all of this. a or b (or c) always consider themselves to be at rest. The universe moves around them. If it is convienient to presuppose some motion on their part, a, b, or c can do so. It just makes calculating the relative motions harder!

From our perspective (watching from above), to resolve a's, b's, or c's perspective, you must subtract the vector motion we see from, say, b (this will transform b into our frame) , and vector add that motion to the other objects.

 

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<a href="http://www.sciforums.com/attachment.php?attachmentid=4002&stc=1" >Vectors</a>


ax = 3, ay = 5

bx = -3, by = 5

To resolve b's perspective:

bx' = bx + 3 = 0
by' = by - 5 = 0

ax' = ax + 3 = 6
ay' = ax - 5 = 0

The result, from b's perspective is that a is approaching from the left.

 

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Why cant I get an image to show?

...OK Got it!

 

As I recall, I posted at least two times entire set of SRT formulas that are answering on your question: how the transit between RF should be arranged.
All what you need is to find those formulas and ... apply them to your specific problem. If you will meet some difficulties at calculations - ask, we will help.

 

I keep bailing you out and look how rude you are to me. Collision of frames you say? OK use mine, you mus dio in order 1 2 3 4 . . .

One 1 for the $
2 4 the show
3 get yer vectors reddy
& 4 2 go
geistkiesel​

 

Ok. Good, they're smashing together. I did figure out the image thing by the way. As for bailing me out... if I ever end up in jail, send money.

 

Let he who is without guilt not to make an appointment to see their probation officer.

Geistkiesel​

 

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Thanks SL.
A question comes to mind about how observer (a) can calculate (b) velocity as being correct. From what I see (b) is approaching (a) quite slowly. Certainly slower than it's actual speed.

So observer (a) would see a slow (b) even though it is travelling quite a bit faster than what (a) can observe.

If (a) is at rest then how can (a) know what the actual velocity is for (b)?

 

QQ,

QQ, with all due respect, your questions make no sense to me.

'a' "calculates" nothing. This is a mathematical transform that allows US (looking down on their world) to calculate what 'a' or 'b' would see. In order to learn and understand this (if you're not going to accept the math) you must cultivate the ability to put yourself in the position of 'a' or 'b' and imagine the result.

This little example of simple Newtonian/Galilean relative motion (it's two people walking, say) is highschool fundamental. My 18yr old daughter understands it intuitively and immediately. How can there be any misunderstanding of this simple example?

'a' is only at rest if you say so, or happen to be 'a'! 'a' only sees what he sees. If he wants his relative velocity to 'b', he pulls out his handy-dandy doppler radar gun. He'll read 6.

SRT has nothing to do with this little problem unless 'a' and 'b' are moving very fast in the x direction (they share the same y component, get it?). If so, 'a' will see 'b' length contracted, mass-increased, and time dilated, moving toward him. If you swap perspectives to 'b', the converse will be true. If 'a' accelerates to match velocity with 'b'...

(and when I say accelerates I mean the possibility of positive or negative acceleration (deceleration), whatever it takes for a or b to match velocities)

...'a', by virtue of having transformed to b's frame, will be the younger, and vice-versa. You've already asked for an explanation of "why" this is so. There's no need to ever ask it again in a physics discussion (speculate all you want in private, I do). Physicists have given the answer. It's the nature of spacetime. Remember, GRT, SRT and all theories were not made up for entertainment purposes, just for the hell of it. They were conceived to explain the results of actual experiments and observations.

Over the years I have read books (yes I can read), science journals, have had college physics (1,2, and 3 - intro relativity - yeah, so the hell what? You uppity college surfer cocktail sipping propagandist...), done tons of web research and posted numerous links here that show one-sided time dilation occurrs (unbelievable that I even have to say that!). Look at our little example. Who is at "rest"? You decide! It's that easy! And if you say 'a' is at rest and 'b' will appear dilated to 'a', then the converse must be true. Also, if you look at the muon-muon scattering cross section, the arguments given in another thread do constitute proof of "reciprocal" observed time dilation. Spend days drawing diagrams of it. It's hard physical proof.

Now note that whaterer positive response I may recieve to my "ask an astronomer" question re mutual observed dilation, with whatever evidence, it will be a fiat by an establishment physicist lackey and will show nothing.

If I sound frustrated, I am. If Yuriy has left, I will not stay here debating idiocies with MacM and Geist, et al. I want to actually learn something of value.

MacM, Geist, et al, you win, you are correct. SRT is dead as a doornail. Compose a paper and send it to NIST, NASA, ESA, IAU, and many others, and have them correct all of the glaring systematic errors they have made by using SRT in satellite calculations, correction of received frequency for fast-moving space probes, predictions of subtle planetary motions, etc.

 

Sorry SL I understand your frustration. I personally do not consider SRT as being "dead". I see great value in AE's work. Always have....

Any way, thanks for responding.....

 

QQ,

You are not the "et al" in the previous post. I don't mind at all helping with genuine questions (as best I can). I happen to be pissed right now re the Yuiry thing. Some may call him a lying, motherhumping communist asshole, but I don't give a crap. He's a physicist and I was learning stuff.

I ask myself, "SL, why do you keep responding to these cranks? Egging them on?" Well, I think it's like a car crash. You just gotta slow down and see how bad it really is. I am on a 12 step program to stop this behavior of mine...

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SL to set the record straight and clear I have only ever once showed my frustration with Yuriy in terms of "arrogant as*h*le". And to tell the truth I deeply regret even saying that.

It is not for me to express myself in such negative ways. It is sad that Yuriy had so much to offer, but for some reason he was unable to communicate what he had to offer in a way that was successful.
Unfortunately others here at the forum are not quite as restrained in the way they express their frustrations.

I do appreciate not being lumbered in the "too hard basket"

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Ha! You should see some of my first discussions with Yuriy. I was ready to slap him upside the head!

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QQ, what is b's 'actual speed'?

 

Pete I am not sure my question is worth salvaging however I have gioven it a little more thought.

B's v = 0.4c as determined by location X where the two frames are to collide.

B's velocity is also determined by C as 0.4c

A's observer notes that Location X is approaching him at 0.4c

So as you can see I have mixed up all my frames as usual.

Location X for example is a default location that for teh sake of this question is unknown by either A or B. All they see is the other moving closer as they both head for location X.
I ask whether A or B can determine the others velocity?

When they are heading to the same location at the same velocity but different angle?

Location X can not be seen by A or B but a collision is seen as possible by C.

Observer A and B can only observe that the other is approaching at a velocity but can not discern the angular lateral movement of each other.


Sorry if I sound so confused....well I guess I am......

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Maybe you have seen this type of scenario before and have a better understanding of the complications?

 

QQ,

Just a friendly question. Do you understand the vector resolution of your scenario and the math behind it? If not, we could work on that. It holds the answer to your confusion...

 

It's a funny thing this math business. Essentially I would consider mysef to be dyslectic when it comes to math.

My mind just sort of goes.....oumph and shuts down the moment I see it.

SuperL I truely appreciate the offer and maybe sometime in the future I will avail my self of it and learn a little math.

I agree that using long handed verbal logic is such a tedius method but unfortunately that is all I have at the moment.

P.s. I am not kidding about my math problems.

 

QQ,

You are not alone. Math is unnatural.

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What's funny is that even with analytic geometry, integral and differential calculus, differential equations, infinite series, complex analysis, and fourier and laplace transforms (minimum for an EE degree), that's just the tip of the iceberg. I am amazed at the math (>95%?) that I've never even seen!

 

I guess that is half my problem, I am aware that mathematics as a field is huge, infinite even [oops did I say infinite]

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Just that years ago I suffered a small stroke that I have since been recovering from. 4 years ago I could barely speak or write for that matter. In fact this forum has been a major factor in my recovery and personal growth to boot.

So mathematics is one of my last frontiers and one that has yet to be properly tackled by me......thus Yuriy's frustration with my math ability is simply reflecting my own frustrations with my own 'math mind" dysfunction.

I do apply a recovery technique that has in the past proved very successful so i look forward to doing some integration and calculus with you and others in the future......ha [btw what is calculus?....ha]