Some problems with light speed barrier.

Yes, indeed from his point of view, the ship keeps reaching greater and greater speeds. It is because of this effect that he can reach a star which is 100 light years away, in only 50 years!

Please Register or Log in to view the hidden image!

 

Log in or Sign up to hide all adverts.

Pete,

No, that isn't correct. For any fuel calculation used to accelerate the rocket must then be increased to include fuel weight. It becomes an unending series. I wrote a program to compute a simular cycle and it compounds until the computer reaches "Overflow somewhere about 3E38 Kg of fuel for a 1 kg rocket.

The reason is that you are accelerating mass using mass to energy at c^2


Now if you add 1kg of fuel to your 1kg rocket, you now have a 2kg rocket including 1kg of fuel.
Correct?

Yes

Which (according to your model) is sufficient to accelerate your rocket to c.
Correct?

No.

 

Log in or Sign up to hide all adverts.

James R.,

Ok. So, you're talking constant acceleration, as seen from Earth, for 1 second.

Or any referece.

Here, you have implicitly used the equation F=ma here to get the force. You have assumed, incorrectly, that a constant force produces a constant acceleration. Relativistically, however, the equation F=ma does not work, and constant force DOES NOT produce constant acceleration. In fact, to keep the acceleration constant, you need to keep increasing the force.

The rest of your argument consequently fails.

You do seem to have missed the following statement:

I was showing that by a linear standard, not considering the gamma function mass to energy conversion based on the speed of light (E=mc^2) cannot accelerate mass to v=c. Now if my arguement fails that would seem to say that you say you can reach v = c and I don't think that is what you want to communicate.

Please Register or Log in to view the hidden image!

Actually, I made a programming error which ompounded the initial 1 kg rocket. The problem becomes Zeno's Paradox. Adding 1/2 as much fuel by weight as it takes to lift the rocket with fuel means you keep adding fuel at 1/2 the size increments. That rapidly resolves to infitesimal steps of added fuel. So forget the example.

 

Log in or Sign up to hide all adverts.

If your argument fails, it means that there is nothing to stop you reaching c except relativity.

And limits to 1kg of fuel plus 1kg rocket.
Just like I said

Please Register or Log in to view the hidden image!

 

Pete,

You do understand that Relativity is not justified in creating such a limit don't you. Unless you can explain to me how an observer affects the phyics of the rocket.

The rocket knows nothing about velocity. It sees enumberable objects all traveling at different velocities. None of which have any impact on the thrust the engine is creating. Its acceleration cannot be restrained by an observer. It knows it is creating a force of acceleration but not anything about velocity.

Fuel consumption is based on the rockets view which is simply F = ma, distance and time for "Delta v = c, not v = c. I know this is in disagreement with the arguements of relativity but I don't accept those arguements.

Thus the conclusion should be that it will accelerate to v => c relative to each observer and simply phase out of existance to such observers by Lorentz Contraction as each relative velocity reachs v = c but continues to exist to observers at less than v = c to him.

 

Computing relativistic rocket without ralativity? Not interested to pursue it any further. It doesn't prove anything. You can't prove speed of light breakable or not breakable with that, since you ignore the very relativity effect.

 

Pete,

That is fine. I'd expect nothing less. I do want to point out for others however, that you (and others) have failed to show any link between an observer and the physics of producing thrust by a rocket, wherein there simply is no relative motion. Enjoy your gamma function. It is one thing to declare F=ma isn't applicable in a situation where there is no relative motion, it is another to explain how an observer can affect the physics of the rocket.

Please Register or Log in to view the hidden image!

Try this one step at a time.

1 - Do you deny F=ma of a rocket. Keeping in mind that it is F=ma that tells us the rocket is accelerating at a given rate by knowing its mass.

2 - Does F=ma change at any mathematical point over time as long as a constant rate of fuel is expended (neglecting the complication of the reduced mass of the total rocket having less fuel by invoking a hydrogen ram jet design which gathers its fuel as it travels through space)?

3 - Do you deny that given mass and force you can calculate a in F=ma?

4 - Does v = at?

Notice none of these questions have any regard to relativity because relativity is not part of the physical equation since velocity is not being determined by an observer but mathematically from well established physics.

5 - Under these conditions do you deny given sufficient fuel a delta v of dv = > c becomes a real possibility?

6 - If not show your limiting factor. Show just how it is an observer precludes the rockets F=ma principle.

 

2inquisitive,

Not really the case. Both Einsteinian relativity as well as Galilean relativity require proper definition for reference frame. Kinetic energy of a rocket, for example, is a parameter measured by observer not in the rocket. This is true for either Einstenian or Galilean relativity. May be, what you meant was, using SR, non-identical result of observation by moving observer and observer at rest would be obtained.

You should carry out a detailed analysis in order to gain a full understanding on the issue. But the basic is this. You need to be very clear about what stuff that come people call 'relativistic mass'. Think about atom with all the moving electron inside. Those moving particles carry kinetic energy relative to a fixed reference frame. Those particles kinetic energy is supposed to be 'reletivistic mass' that when we determine the atom mass, we include them as 'rest mass' as well. This makes it hard to say this and this are rest mass or such and such are 'relativistic mass'.

You can take away certain kinetic energy of particles which would cause the object/matter temperature to drop. Relativistic mass of a moving rocket is partly the rocket kinetic energy. you can't take this kinetic energy to power the rocket whithout causing the rocket velocity to drop.

 

In SR, the observer does not affect the physics of the rocket. You appear to be confused.

Agreed.

So you accept Lorentz Contraction? What about time dilation?

I'm not sure of your reasoning... Can you help me out?

Let's say you've launched the rocket, with me on board, headed toward the Andromeda Galaxy, 2 million light years away.
I'm accelerating at a constant rate of 100 km/s/s.

According to your model:
How long will it take me to reach c?
Do you and I agree on this time?
How far have I travelled before I reach c?
Do you and I agree on this distance?
How far am I from my destination at this time?
Do you and I agree on this distance?

 

(actually, that was Paul T... I expect it was just a typo, but I'm pointing it out just in case)

 

Stop poluting this forum with this kind of nonsense. We have tried to explain it to you. We failed. Now don't pretend you know about this kind of stuff.

 

quote:

"From the rocket's point of view, it is not moving at all. The rocket is stationary in its own reference frame. It has zero velocity and zero acceleration. From the rocket's point of view the universe accelerates."
===============================================================
OK, I take it this means the rocket and observer on board the rocket are in an inertial
frame of reference, and the universe is in a non-inertial frame.

quote:
"An observer in the rocket is in a non-inertial frame of reference, for which even the above equation must be modified."
=============================================================

Here is where I get confused. How did the observer in the rocket get from an inertial
frame to a non-inertial frame? And I do know the non-inertial frame is the accelerating
frame. How can the observer on the rocket be in an inertial frame and the universe be
in a non-inertial frame?

 

I have a different perspective on this problem to the one James presented.

Hard to answer without defining in which frame you're measuring acceleration, and whether mass is rest mass or relativistic mass. If relativistic mass, need reference frame again.

I'll assume that:
m = rest mass of rocket
a = acceleration measured in the rocket's instantaneous inertial frame.

In this case, F=ma

No

No, but note that the a you calculate is the acceleration in the rocket's frame.
This is not the same as the acceleration in the observer's frame.
For acceleration in the observer's frame, you must use the rocket's relativistic mass.

Yes, if:
v = velocity of rocket relative to the observer
t = time in the observer's frame
a = constant acceleration of the rocket in the observer's frame

So this where the argument fails.
a is not constant in the observer's frame, and both a and t are frame dependent.

 

Pete (and others),

Others, I'm not ignoring you, it is just that Pete seems the closest to right for the point I was trying to make.

I indeed have no confusion about what is claimed regarding gamma function and observers or that without observers there is no velocity measurement. But that really has not been the point. The point is by phyics of the rocket we actually care less about the observer.

What the observer sees is not the issue, it has no bearing on the performance of the rocket. My rocket is closed, no windows and no external sensors. I am using a closed system based on known facts about rockets and physics.

Since there is no declared "relative velocity" gamma doesn't come into the picture. I know I am firing my rockets. I know the mass of my craft. My computer will convert the known information and measured force into "delta velocity" (that is a velocity change from the time I started the engines), and there is indeed no restraint on my rocket achieving a terminal velocity that is v = > c by my measurements, by my calculation, by my physics.

I do not care what observers claim to see. That is perception not physics. The rockets F=ma is physics of the rocket. Gamma has abolutely nothing to do with the rockets physics.

This is the point that I have tried to make for a long time. Your Relativity is a miss application of the theory in self-propelled cases. You tend to see the limnitation because of the Relavistic Mass conclusion of particle accelerators. But particle accelerators are not self-propelled particles, you have relative velocity between the particle and the accelerating field. Here gamma is correct (even though you make erroneous conclusions about the cause and I personally do not believe mass changes at all).

For those that see this as "pollution of the forum" let me suggest it is more in keeping with retaining sound physics understanding and not throwing reason to the wind over Relativity.

My position is that since there is no test, no data and no observation that supports your claim that gamma somehow restricts the rockets performance (F = ma) that in fact what will happen is that the rocket achieving a v = > c velocity to an observer simply ceases to exist to that observer by Lorentz Contraction. The observer cannot restrain the acceleration of the independant rocket.

Now prove me wrong by other than lip service. Show me evidence that Relativity has any bearing what-so-ever on the rockets performance. Show me evidence that an observer will in fact not see the rocket continue to accelerate and simply vanish by other than declarations that Relativity applies and the gamma function limits the rocket. I am anxious to see such actual evidence.

The repeated claim that you all have told me many times and that I imply do not understand is false. I undertand very well. What you don't seem to understand is that I reject your conclusions in that there is no such evidence or rational explanation for such a conclusion and my view is consistant with observation and logic.

 

Crisp,

I don't know where it has been but the following post just showed up in my e-mail and I don't see it within the last two pages but I did want to respond to it.

Please don't continue to state falsely that I don't understand. I damn well do. The fact is I reject your conclusions outright and state without hesitation that you are taking a position that is absolutely unjustified with regard to Relativity and a self-propelled object. You simply have NO evidence to support your conclusion. Your application of Relativity in this case is in absolute contrast to Relativity itself. There is no relative velocity in the physics of the rocket, therefore there is no gamma restraint to its performance and ability to exceed a "Delta v = > c" What you keep talking about is perception of an observer. I am not contesting gamma in regard to the "Perception" but state without hesitation an observers perception doesn't and cannot alter the performance of the rocket. Hence the rocket will continue to acclerate beyond your precious v = c limit prediction. It will vanish by Lorentz Contraction and do exactly as I have maintained and which is supported by observation, unlike your claim which is not.

I know my position is not favored by Relativists but that matters not, you, nor they can justify the imposition of gamma onto the performance of the rocket where there is no relative velocity. You cannot justify or show evidence that somehow your "Gamma" perception in anyway is real and limits the ultimate "delta velocity" of the rocket. It is conjecture pure and simple and it forgoes any logic or purpose what-so-ever.

Please show us where Relativity test data or observation shows any such act of nature. Where principles of relative motion "Observation" has ever affected the raw physics of an inertial system where there is no relativ velocity. There is none, you are living in a dream world all wrapped up in your priceless mathematics which do not represent reality. Show otherwise or stop talking so high and mighty.

Ditto - Either show evidence supporting your claim or stop making the claim. I don't have to pretend, I have sufficient reason so as to be able to resist the ludrirus arguements of Relativity where Relativity doesn't apply, which is in the physics of an independant inertial system

 

A captain aboard a starship can certainly accelerate forever, according to his watch. He will continue to accelerate at a constant rate, forever, according to his instruments. He will be able to fly between stars in milliseconds, according to his watch. It is in this sense that MacM asserts that he is going faster than light.

The problem with this assertion is simple: you're combining measurements from two different frames. You assume that the Sun and Alpha Centauri are, say, four light-years apart. You then assume that the captain of the starship, being able to travel that distance in a millisecond, must be going quite a bit faster than light. You are mixing frames. You're measuring the distance between stars in a frame where they are at rest with each other (the Sun is roughly at rest with respect to other nearby stars), and then measuring time in a frame that is moving very quickly with respect to them (the starship). That's a no-no, MacM. You assertion that the captain is going faster than light is understandable, in a way, but we physicists don't like to mix measurements from different frames.

Rather than crossing four light-years in a millisecond, the captain actually sees the entire universe ahead of him severely length-contracted. The distance between the Sun and Alpha Centauri does not look at all like four light-years to him -- it looks like inches.

Now, what does an Earth-bound observer see? He sees the starship asymptotically approach the speed of light. Its thrusters become less effective against the apparent relativistic mass of the spaceship. The communication coming from the ship also indicates that the captain's clock is running much more slowly than one on Earth. All of these effects are interrelated, and cannot be separated. Time dilation and length contraction are really just two ways of viewing the exact same effect.

- Warren

 

Chroot,

I never thought the day would come but thank you chroot. You are the first to put this into proper perspective. While I would have some minor differences in certain details of your description in general we are very much in agreement.

I simply find it inappropriate to declare the observer as being the point of physics. That is perception, from the point of the rockets physics it continues to produce thrust and continues to shorten the distance traveled. But as I stated earlier I have a closed inertial system. I am not measuring distance. I am computing change in velocity via F=ma and time and by time acceleration computation would to be exceeding v = c which would account for my early arrival. That is if it took 1 year to reach A.C. I would believe with just cause I had reached and average of 4.3 c. To me that is the physics not what other parties observe.

 

However, by the captain's own ruler the distance between him and Alpha Centauri would not be 4 light-years anymore; it would be only inches. The captain himself is not able to say he's going faster than light, because his own ruler and watch wouldn't agree with that. He could truthfully say "I covered what appears to be 4 light-years in the rest frame of Alpha Centauri in what appears to be one millisecond on my watch," but that statement is not very useful, and rather against the conventions physicists use -- namely, not mixing frames.

- Warren

 

Hi MacM,
I'm still not clear on your argument, which makes it difficult for me.
Are you maintaining that the acceleration measured on the ship is the same as the acceleration seen by a stationary observer?

If so, it doesn't seem consistent with accepting length contraction and time dilation.


Can you step me through this experiment:
Let's say you've launched the rocket, with me on board, headed toward the Andromeda Galaxy, 2 million light years away.
I'm accelerating at a constant rate of 100 km/s/s.

According to your model:
How long will it take me to reach c by my watch?
Do you and I agree on this time?
How far have I travelled before I reach c? How would I measure this?
Do you and I agree on this distance?
How far am I from my destination at this time?
Do you and I agree on this distance?