Superluminal motion. How's that possible?

[DaveC426913]

vish, your questions are confused. Ask one at a time.

Two objects traveling towards each other track their motion with respect to a THIRD object (say, Earth) between them. They each calculate that they are moving wrt Earth at .9c.

When they each look beyond Earth, they see the other spaceship moving toward them at .994c (180/181).

This you must accept: addition of velocities at relativistic speeds does not occur as you expect. It happens as Dickfore explained in post 20. Remember, relativsitic motion involves time dilation; you cannot count on how time passes in other frames of reference.

As for the glass balls >20mm, I don't know what that has to do with anything.

 

[vish_al210]

As for the glass balls >20mm, I don't know what that has to do with anything.

They are not observing Earth or vice versa but observing each other as they travel towards each other, each with a velocity of .9C.
And the point of two glass spheres >20mm was, in response to the option of an elastic collision. I was aspiring to know if the impact of the two objects would be an equivalent of one of the sphere's moving towards the other sphere(stationary) at 1.8C. (I have been going bonkers about this assumption of mine for a few years now.)
And if relatively, the speed varies by only 0.09__ value(in the above spoken case..), the why do I experience a drastic change in velocity between me standing at a station and observing a train crossing me, and me traveling in a train at a speed equivalent to the train being observed and observing it.
if the speeds of the objects in much lesser than light then the relative speed seems to double but if the objects are moving at speeds closer to the speeds of light then the relative speed is only marginally more. I am not being sceptical of the great minds that worked a major chunk of their lives unlike me in understanding and relating this phenomenon, but the equation seems to me (as of now.. based on the nothing that I know) like a failsafe, emanating from the initial consideration of the notion about the elusive speed of light.. but yeah, .9C also would e very hard to achieve...

vish, your questions are confused. Ask one at a time.

;) sorry.. but my questions and rattlings are an extention of my present state.. you shld expect no less or more...

 

[Doc Al]

I still don't get it.. I am not questioning what you all have earlier stated but am only trying to understand.
Given data:
a. distance between the two objects is 100 light seconds (effective length traveled by light in 100 sec)
effectively A and B both would contact each other at 50 light seconds from their respective start points, considering both experience similar conditions and friction etc..
travelling at 0.9C each they meet after 50/.9, i.e., after 55.556 seconds.

That's only according to Earth observers. A and B themselves would measure different distances and times.

Shouldn't the observer sitting in A feel that B was moving at 1.8C. As the light from B to A is traveling at C, and A is traveling at .9C towards the light, while the source of the light from B (B itself) is also moving towards A with speed .9C

No, speeds don't add up like you think they do.

They are not observing Earth or vice versa but observing each other as they travel towards each other, each with a velocity of .9C.
And the point of two glass spheres >20mm was, in response to the option of an elastic collision. I was aspiring to know if the impact of the two objects would be an equivalent of one of the sphere's moving towards the other sphere(stationary) at 1.8C. (I have been going bonkers about this assumption of mine for a few years now.)
And if relatively, the speed varies by only 0.09__ value(in the above spoken case..), the why do I experience a drastic change in velocity between me standing at a station and observing a train crossing me, and me traveling in a train at a speed equivalent to the train being observed and observing it.

That's because the speeds of you and the train are much smaller than the speed of light.

if the speeds of the objects in much lesser than light then the relative speed seems to double but if the objects are moving at speeds closer to the speeds of light then the relative speed is only marginally more.

Exactly right. For small speeds, the speeds add up just like you'd think. For example, if you are on a train traveling at 50 mph with respect to the track and another train is traveling towards you at a speed of 50 mph with respect to the track, then you'd see the other train approaching you at very close to 100 mph. (Actually, very slightly less--but close enough.)

But as speeds get closer to the speed of light, they no longer add so simply. If you play around with the addition of velocity formula, you'll see that. As far as understanding how it all works, you'll have to study a bit of relativity.

 

[vish_al210]

Thanks Doc_Al. and also Dave and everyone else...

But forgive me... it might take some more time and understanding for it to sink in .. I guess u understand...

but could you tell me if this is possible as asked in my earlier post..

I was aspiring to know if the impact of the two objects (each moving at .9c) would be an equivalent of one of the sphere's moving towards the other sphere(stationary) at 1.8C. (I have been going bonkers about this assumption of mine for a few years now.)

 

[Doc Al]

but could you tell me if this is possible as asked in my earlier post..

I was aspiring to know if the impact of the two objects (each moving at .9c) would be an equivalent of one of the sphere's moving towards the other sphere(stationary) at 1.8C. (I have been going bonkers about this assumption of mine for a few years now.)

No. There's no such thing as one sphere moving towards the other at 1.8c--it's physically impossible. A collision between two spheres each moving toward each other at 0.9c (with respect to the earth) is equivalent to one being stationary and the other moving at 0.994c.

 

[vish_al210]

but what is the individual energies of the two sphere's (each moving @ 0.9C) and when they collide what would be their result, (let us consider some tangible mass).
Is that energy equation the same as that of one sphere standing and the other impacting it at 0.994C.. I am really puzzled.. I believe and hope u have the answers.. as what I am considering and thinking would have already been thought of and answered...
Thank you for your patience though..

 

[Doc Al]

but what is the individual energies of the two sphere's (each moving @ 0.9C) and when they collide what would be their result, (let us consider some tangible mass).
Is that energy equation the same as that of one sphere standing and the other impacting it at 0.994C.. I am really puzzled.. I believe and hope u have the answers.. as what I am considering and thinking would have already been thought of and answered...

Realize that whether you see two objects moving at 0.9c or one stationary and the other moving at 0.994c is just a matter of reference frame. It's the same collision! (The kinetic energy of each object depends on the reference frame, of course.)

 

[vish_al210]

So .. the kinetic energy of the object is different if the observer is at different points.. How does the observer alter the kinetic energy of a moving object ?
The kinetic energy/momentum of an object is relative to the energy consumed in moving forward right?? or am I wrong??
And I do not mean the kinetic energy alone but the total energy of A.. and separately the energy of B.
I mean throwing a ball on a wall with speed V1 is not the same as throwing the wall with speed V1 on the ball... It is different right..

 

[vish_al210]

So finally the general simplified equations neither work in infinitesimal conditions or in substantially large scale conditions...

 

[DaveC426913]

but what is the individual energies of the two sphere's (each moving @ 0.9C)

Kinetic energy is frame-dependent. Two objects moving wrt each other have kinetic energy as measured by their relative speeds. Two objects at rest wrt each other have zero kinetic energy.

Picture an apple whizzing past Earth at .9c. The kinetic energy of that apple from Earth's frame of reference is dependent on exactly two properties: the apple's mass and its velocity. Its kinetic energy would be quite high, yes?

Now picture an orange whizzing alongside the apple, same speed, same path. What is the apple's kinetic energy wrt the orange? In the orange's frame of reference, the apple is at rest, therefore its kinetic energy is zero.

Now, picture the apple and orange both whizzing toward Earth from opposite directions at .9c. Earth calculates each kinetic energy based on its mass and its velocity wrt Earth.

But what does the orange calculate about the apple's kinetic energy? Well, the apple is moving towards it at .994c, so that's what's used to calculate its kinetic energy.

You add kinetic energy using the same formula that use to add their velocities, i.e.: .9+.9 = .994

 

[vish_al210]

But then what about momentum, is that also frame of observation dependent??

 

[Doc Al]

But then what about momentum, is that also frame of observation dependent??

Of course. Anything that depends on velocity is frame dependent.

 

[Dickfore]

The op needs to enroll in an introductory course in Special Theory of Relativity.

 

[vish_al210]

@ Everyone..
Thanks,...
But I am still not clear.. but understand that u all must be stating the right thing. I tried reading on this topic, but understand that just skimming the articles won't help..
So I shall try a little more indepth reading on this subject.
Well ;) pray for me guys... That I have a clearer head...(by that I don't mean blank..)
Thank you all for your patience. though I am a lot more muddled//confused in the head right now, I know that my understanding is wrong.. Now! that's a start...
All of you folks, take care... Wishing you all a merry Christmas//Kwanzaa// or well to everyone a wonderful year ending..
Take care...

 

[DaveC426913]

@ Everyone..
Thanks,...
But I am still not clear.. but understand that u all must be stating the right thing. I tried reading on this topic, but understand that just skimming the articles won't help..
So I shall try a little more indepth reading on this subject.
Well ;) pray for me guys... That I have a clearer head...(by that I don't mean blank..)
Thank you all for your patience. though I am a lot more muddled//confused in the head right now, I know that my understanding is wrong.. Now! that's a start...
All of you folks, take care... Wishing you all a merry Christmas//Kwanzaa// or well to everyone a wonderful year ending..
Take care...

Do not be shy to ask questions, even the most basic ones. We will fall all over ourselves to answer questions. That's why we're here.

 

[vish_al210]

Thanks Dave. And well I am not ashamed or shy of asking questions... It is good that finally the question/condition boiling in my head for over a few years is at least broken down...
I am not all satisfied as it shattered a myth in my head(well that was expected!).
But better shatter the myth than enjoy its fancy..
But I suppose that if eventually, something does travel faster than light what would we be able to see.. I mean see of the object...as our perception is light. I know we got equations and inferences to showcase that it wld not be possible... But just suppose that the equation has a loop hole.. as with everything else there is an exception..
What would we see or observe(I mean seeing in plain simple terms)

 

[DaveC426913]

But I suppose that if eventually, something does travel faster than light what would we be able to see.. I mean see of the object...as our perception is light. I know we got equations and inferences to showcase that it wld not be possible... But just suppose that the equation has a loop hole.. as with everything else there is an exception..
What would we see or observe(I mean seeing in plain simple terms)

Well, what you're asking is "What would the laws of physics be like if the laws of physics were different than what they are?"

The problem with that is that the answer can be anything you want.


But I know that's never satisfactory, so I'll give you a teaser.

Relativity does not forbid massive particles moving faster than the speed of light; it only forbids them from reaching and transitioning the speed of light. This leads to the hypothetical possibility of particles existing that always travel faster than the speed of light. These hypothetical particles are collectively known as tachyons (fast ones). They normally travel much faster than c, but when they absorb energy, they actually slow down closer and closer to c. The closer they get to c, the more energy it takes to push them closer. No amount of energy can get them to slow down to c or slower. They are mirrors of our slower-than-light particles.

What is interesting about them is that, to us, they would be traveling backwards in time. In their interactions, effect would precede cause.

 

[vish_al210]

If I consider an object moving past me ..(not through me.. I want to live ;) ) with a speed greater than light...
then I could draw lines form each of its state towards me in the path to indicate the light traveling from the object @ C.. Now as the light would take different time intervals to reach me(slower than the passage of the object), is there a possibility of me seeing the object as an extended line or multiple objects...I mean if we do find an object moving at speed greater than C, how would we identify it?

 

[Dickfore]

Tachyons (from Greek takhus = swift) are particles considered from a purely theoretical point of view that can and always travel faster than c. They have the peculiar property that they accelerate when their kinetic energy decreases, reaching infinite speed when the kinetic energy is zero (or having zero kinetic energy when they accelerate to infinite speeds). Mathematically they should have imaginary rest mass.

 

[henryc09]

I think something you need to get your head around is that there is nothing fundamentally that you can measure velocities with respect to. On Earth we tend to measure velocities w.r.t the earth, but when you consider the universe as a whole there is nothing you can do this with. It therefore only really makes sense to consider measuring velocities w.r.t a given frame of reference. However, experimentally it was found that regardless of an observer's relative motion to a beam of light, the same speed of light is ALWAYS measured. Special relativity provides a way of knowing what people in different reference frames will observe, and leads to the velocity addition formula used earlier which prevents anything from traveling faster than the speed of light! It's strange, I know! But it all follows from the experimental fact that the speed of light is the same regardless of relative motion.

 

[DaveC426913]

Tachyons (from Greek takhus = swift) are particles considered from a purely theoretical point of view

Actually, as previously mentioned, they're not even theoretical; they're hypothetical. There is really no reason to even suppose they might exist. It is simply that they do not violate relativity.

 

[Dickfore]

Actually, as previously mentioned, they're not even theoretical; they're hypothetical. There is really no reason to even suppose they might exist. It is simply that they do not violate relativity.

As much as I read, there are theoretical reasons to suppose their existence in some theoretical models. Thus, 'theoretical' = 'hypothetical' as long as those models are just hypotheses.

 

[vish_al210]

Well.. I was presenting a hypothetical situ.. Anyway... thanks a lot everyone...for your guidance and patience.
And yes I am clear that my assumption was wrong (about the two bodies moving at 0.9c relating to 1.8c).. and I will do the reading required to make me understand the same.
You needn't discuss the hypothetical case as (well it is hypothetical and) it has been discussed in http://en.wikipedia.org/wiki/File:Tachyon04s.gif
And I understand that the discussion on that is hypothetical and does not prove their existence as such. And my knowledge on this is very menial or non-existence... ;)
Well thanks a lot... take care...