Can you determine absolute motion?

[SeventhSigma]

AFAIK Newton proposed absolute space (such as with his rotating bucket experiment) and it got hammered away a bit by Mach, but then Einstein came forth and basically said "space isn't absolute -- spacetime is." So in other words, the spacetime continuum is an "absolute" concept where you're trading off motion in time for motion in space. Acceleration and gravity, according to Einstein, are the same thing. Space and time fall out of sync in different inertial frames.

 

[Physicist1231]

Physicist1231, this is a complete lack of understanding of Einsteinian spacetime. You are using a classical Newtonian model, where space and time are absolute and unchanging backdrops against which all things can be measured.

The classical Newtonian model has been replaced with the Einsteinian model, which has been shown to be correct in what is arguably the most well-tested theory in the history of science.

The very fundamental principle of Einsteinian relativity is exactly this: simultaneity of events is relative to the observer's frame of reference. All other phenom fall out of this one.

Your arguiments are all based on an out-of-date model that has been shown to be false in literally uncountable experiments.

It is not really a lack of understanding of Einsteinian spacetime rather reviewing history as to why the classical Newtonian model has been replaced with the Einsteinian model.

Doing the research (really getting off topic though) you will find that the notion if time dilation was perceived where an object in motion at a high rate did not seem to tick the same time as it did on earth. This may have been with the satelites in space or perhaps rocket launches. We as the world saw a phenomonon and wanted to find out what was causing this. Galileo tried to do this with the Galilian transformation. This was using the Newtonian modle and the assumption that space and time have rigid values though they can be perceived differently. This proved to be inaccurate (in 3d space where it did work in a one dimensional space, the level of inaccuracy increased as speeds increased). About the same time the failure was noted the Lorentz Transformation came about with a completely new thought process of time and space being flexible. Einstein took this idea and ran with it to develop GR and SR. Thus completely abandoning the Newtonian physics.

This was a very dramatic and rapid change in the scientific thought process. So rapid in fact that no one looked back to see why the Galilean Transformation was incorrect while using Newtonian physics (which ALWAYS worked accuratelty for any previous experiment).

In short things can be explained using Newtonian Physics using a rigid strucutre of spacetime, its just that Galileo failed at that attempt and science ran in a different direction.

One of the largest supporting expiriments that is used to support the theories of SR and GR for time dilation is the Hafele–Keating expiriment. This has since been debunked by even Dr. Keating himself.

http://www.google.com/url?sa=t&source=web&cd=4&ved=0CCoQFjAD&url=http%3A%2F%2Fwww.shaping.ru%2Fcongress%2Fenglish%2Fspenser1%2Fspencer1.asp&ei=yl7JTbnALs3Lswao75CQAw&usg=AFQjCNHWdDddqaNxYeKn-egojeHvd64BRQ

http://www.google.com/url?sa=t&sour...75CQAw&usg=AFQjCNFC78HsYCpF2GNd_dvwtC0_IU0-fg

http://www.google.com/url?sa=t&source=web&cd=9&ved=0CFEQFjAI&url=http%3A%2F%2Fwww.phil-inst.hu%2F~szekely%2FPIRT_BP_2%2Fpapers%2FNAWROT_09_FT.doc&ei=yl7JTbnALs3Lswao75CQAw&usg=AFQjCNGuyJ40-VXlCoDs0uHomjbfDDSZJw

http://www.anti-relativity.com/hafelekeatingdebunk.htm

The raw data was not looked at by majority of the scientific community because of the attitude of "hey they did it and it worked!" rather than looking at the results as to why the original conclusion was that it worked.

 

[SeventhSigma]

Wait a second here are you trying to say that time dilation is a farce?

 

[JesseM]

We can make it more simple.

Light A is at -10ls,0,0
Light B is at 10ls,0,0
Observer is at 0,0,0

Light A and B emit light at the same time

Provided that the entire setup is motionless the observer will see the lights flash at the same time

Move the observer to 0,5ls,0 and he will observe the same thing just takes a fraction of a second longer to see them.

Move to 0,5ls,5000ls and he will still observe that both happened at the same time. just takes a lot longer to see it.

How does this conflict with jtbell's statement that events are only simultaneous in one frame? If those two observers are at rest in the coordinate system where you are giving the position coordinates, then they are normally said to share the "same frame", it doesn't matter if their positions are different. If the two observers have different velocities and just happen to be at those positions when the light strikes them, then as I already told you before, saying events are simultaneous in your frame is not the same as seeing the light from them simultaneously, in their own frame the activation of light A and B may not have happened at the same distance from their own position, in which case seeing the light from them simultaneously implies they did not occur simultaneously in their own frame.

Nevertheless jtbell's statement is slightly inaccurate if we are talking about a space with more than 1 dimension, in this case it is possible for two frames to judge the same pair of events to be simultaneous, but only if the spatial axis between the events is orthogonal to (at right angles to) the axis of motion between the two frames. For example if two events happen at x=0,y=0,t=0 and x=10,y=0,t=0 in my frame, and you are moving along my y-axis but you have zero velocity along the x-axis, then in your frame the events are still simultaneous.

 

[DaveC426913]

It is not really a lack of understanding of Einsteinian spacetime rather reviewing history as to why the classical Newtonian model has been replaced with the Einsteinian model.

Because it has been shown to be false. You made incorrect assertions. We showed them to be wrong. This should have been a very short thread.

Galileo tried to do this with the Galilian transformation. This was using the Newtonian modle and the assumption that space and time have rigid values though they can be perceived differently. This proved to be inaccurate (in 3d space where it did work in a one dimensional space, the level of inaccuracy increased as speeds increased). About the same time the failure was noted the Lorentz Transformation came about with a completely new thought process of time and space being flexible. Einstein took this idea and ran with it to develop GR and SR. Thus completely abandoning the Newtonian physics.

This was a very dramatic and rapid change in the scientific thought process. So rapid in fact that no one looked back to see why the Galilean Transformation was incorrect while using Newtonian physics (which ALWAYS worked accuratelty for any previous experiment).

In short things can be explained using Newtonian Physics using a rigid strucutre of spacetime, its just that Galileo failed at that attempt and science ran in a different direction.

So, you are championing classical Newtonian model with fixed background of space and time, or are you here to champion the Galilean Transform? If the former, every experiment in the last 80 years has refuted it. If the latter, why are you not using it to make your case here? Why are we still discussing events of simultaneity in classical Newtonian model with no modifications?

We have been taking your statements at face value. And at face value they are incorrect.

Seems kind of disingenuous to claim that you've been playing your cards close to your chest all along, stringing us along with all this talk of Newtonian classical space and time.

Are you conniving aforethought? Or are you backpedaling to save face? Got to be one of the two.

Perhaps it's time to close this thread and open a new one making your case for the resurgence of the Galilean Transform.

 

[JesseM]

One of the largest supporting expiriments that is used to support the theories of SR and GR for time dilation is the Hafele–Keating expiriment. This has since been debunked by even Dr. Keating himself.

http://www.google.com/url?sa=t&source=web&cd=4&ved=0CCoQFjAD&url=http%3A%2F%2Fwww.shaping.ru%2Fcongress%2Fenglish%2Fspenser1%2Fspencer1.asp&ei=yl7JTbnALs3Lswao75CQAw&usg=AFQjCNHWdDddqaNxYeKn-egojeHvd64BRQ

http://www.google.com/url?sa=t&sour...75CQAw&usg=AFQjCNFC78HsYCpF2GNd_dvwtC0_IU0-fg

http://www.google.com/url?sa=t&source=web&cd=9&ved=0CFEQFjAI&url=http%3A%2F%2Fwww.phil-inst.hu%2F~szekely%2FPIRT_BP_2%2Fpapers%2FNAWROT_09_FT.doc&ei=yl7JTbnALs3Lswao75CQAw&usg=AFQjCNGuyJ40-VXlCoDs0uHomjbfDDSZJw

http://www.anti-relativity.com/hafelekeatingdebunk.htm

I don't think any of these papers has been published in a peer-reviewed mainstream source, you can find all sorts of crackpot claims if you look around at random websites, including authors who apparently misunderstand the techniques used to get final values from the raw data, see the note in blue here. In any case the Hafele-Keating experiment has been repeated at later times with more accurate clocks and the results continue to confirm the predictions of relativity, see for example http://www.npl.co.uk/upload/pdf/metromnia_issue18.pdf where they found:

On return to NPL the traveling clock was predicted to have gained 39.8 ns, including
an additional geometric factor. This compared remarkably well with a measured gain of 39.0 ns. We estimated the uncertainty due to clock instabilities and noise to be around ±2 ns.

 

[Physicist1231]

Wait a second here are you trying to say that time dilation is a farce?

Not completely. People percieve time differently but this does not mean that Time in an absolute sense is flexible. Just able to be perceived differently. Again the difference between Actuallity and Perception.

 

[SeventhSigma]

Not completely. People percieve time differently but this does not mean that Time in an absolute sense is flexible. Just able to be perceived differently. Again the difference between Actuallity and Perception.

But relativity is all about coming to conclusions *after all observations have been made*. Besides, perception is all we have to define our reality, so evidence has to be taken very seriously. And the evidence, to date, points to relativity as being more consistent than the Newtonian sense where "absolute space" is concerned.

 

[JesseM]

Not completely. People percieve time differently but this does not mean that Time in an absolute sense is flexible. Just able to be perceived differently. Again the difference between Actuallity and Perception.

In relativity you are free to believe in the "actuality" of absolute space and time (though most people who accept relativity probably see no need for such an idea, as 1MileCrash suggested), as long as you accept that there would be no experimental way to determine the truth about things like absolute velocity and absolute simultaneity. If you think there would be, then you must reject some aspect of relativity, but you're going to have a very hard time constructing a theory that rejects some part of relativity but is consistent with so much experimental evidence that seems to support it.

 

[Physicist1231]

Perhaps it's time to close this thread and open a new one making your case for the resurgence of the Galilean Transform.

Tried that and got shot down and the thread was deleted... so I am asking individual questions to gain a better understanding.

 

[Physicist1231]

But relativity is all about coming to conclusions *after all observations have been made*. Besides, perception is all we have to define our reality, so evidence has to be taken very seriously. And the evidence, to date, points to relativity as being more consistent than the Newtonian sense where "absolute space" is concerned.

So if no one perceives an event did it actually happen? If we only base reality on what we as a group or individuals percieve then we will wind up with holes of unexplained things.

Classic example. If a tree falls in the woods and no one hears it, did it make a noise?

 

[Physicist1231]

In relativity you are free to believe in the "actuality" of absolute space and time (though most people who accept relativity probably see no need for such an idea, as 1MileCrash suggested), as long as you accept that there would be no experimental way to determine the truth about things like absolute velocity and absolute simultaneity. If you think there would be, then you must reject some aspect of relativity, but you're going to have a very hard time constructing a theory that rejects some part of relativity but is consistent with so much experimental evidence that seems to support it.

so what you are saying is that i have a chance?

 

[DaveC426913]

Tried that and got shot down and the thread was deleted... so I am asking individual questions to gain a better understanding.

But your premises are all wrong.

You postulate an omniscient viewpoint where none exists.

You have an arbitrary number of observers at arbitrary locations. They observe some events and disagree on when they occurred.

Start from there.

So if no one perceives an event did it actually happen? If we only base reality on what we as a group or individuals percieve then we will wind up with holes of unexplained things.

Classic example. If a tree falls in the woods and no one hears it, did it make a noise?

Let's not get philosophical.

In this practical case you have observers. They observe. We need to explain what they observe.

 

[JesseM]

so what you are saying is that i have a chance?

Only if by "chance" you mean that it's logically possible to have a theory where almost all phenomena behave as relativity predicts but with some rare and so-far unobserved exceptions that might established a preferred frame (something like a Lorentz ether theory where nearly all phenomena length-contract and time-dilate when moving relative to the preferred frame, but there are a few exceptions). But you don't have a chance if you want to disprove relativity just by thought-experiments and theoretical arguments, it is provably self-consistent mathematically, the only way to show it is flawed would be to go out and do some new experiment no one has ever tried and find clear-cut observations of a phenomena that doesn't obey Lorentz-symmetric laws.

 

[Physicist1231]

But your premises are all wrong.

You postulate an omniscient viewpoint where none exists.

You have an arbitrary number of observers at arbitrary locations. They observe some events and disagree on when they occurred.

Start from there.



Let's not get philosophical.

In this practical case you have observers. They observe. We need to explain what they observe.

You say that none exists. Do you say that becase we have never discovered one? Thousands of years ago if I said that atoms existed I might get the same reaction.

 

[Physicist1231]

So, you are championing classical Newtonian model with fixed background of space and time, or are you here to champion the Galilean Transform?

Actually I would support the Newtonian model but not really the Galilean transform. Galileo had the right idea but the formula was incomplete.

 

[DaveC426913]

You say that none exists. Do you say that becase we have never discovered one? Thousands of years ago if I said that atoms existed I might get the same reaction.

Correct. Thousands of years ago we did not have the scientific method. We've advanced a little since then.

Consequently, in this day and age we try not to explain the universe by resorting to the existence of God and his Omniscient viewpoint.

You'll not make a lot of progress here on PF singing that tune.

 

[Physicist1231]

Correct. Thousands of years ago we did not have the scientific method. We've advanced a little since then.

Consequently, in this day and age we try not to explain the universe by resorting to the existence of God and his Omniscient viewpoint.

You'll not make a lot of progress here on PF singing that tune.

LOL I was not trying to bring The Almightly into this. I could... but won't in this case. I was simply using the Omnipotent POV to express it is not limited to Space and time.

But part of theories is to find out the implications of what you are saying.

If we were (and don't shoot me for saying) to use Newtonian Physics in calculating things like time Dilation then we would not be removing Relativity. Merely, redefining it. Is it completely impossible that NONE of GR and SR is wrong?

 

[DaveC426913]

LOL I was not trying to bring The Almightly into this. I could... but won't in this case. I was simply using the Omnipotent POV to express it is not limited to Space and time.

How can you have the latter without the former? That's a rhetorical question. The latter implies the existence of the former. We do not ascribe to the existence of the former.

An omnipotent PoV is beyond science. You cannot invoke it as a valid argument.

If we were (and don't shoot me for saying) to use Newtonian Physics in calculating things like time Dilation then we would not be removing Relativity. Merely, redefining it. Is it completely impossible that NONE of GR and SR is wrong?

Why don't you start with the results of the experiments? We have ample evidence of time dilation; Einsteinain SR and GR explain it very well. The Newtonian model does not.

Why are you trying to fix what ain't broke? What is the impetous driving your desire to find another answer when we have an answer?

 

[Dale]

Thousands of years ago if I said that atoms existed I might get the same reaction.

Thousands of years ago the ancient Greek philosophers postulated atoms, that is where the word came from. But that is not the point. The point is that there is no experimental evidence in favor of an absolute reference frame. This means that it is not necessary in order to explain experimental results and, if it exists, it does not significantly impact any experimental data obtained to date.

I was simply using the Omnipotent POV

The word is "omniscient" meaning all-knowing, not "omnipotent" meaning all-powerful.

If we were (and don't shoot me for saying) to use Newtonian Physics in calculating things like time Dilation

Nonsense. Time dilation is not part of Newtonian physics.

Re your OP. There is no way to detect absolute motion. Your proposed device would not register any inertial motion effects. You should learn the Lorentz transform and do the derivation yourself. It will be very instructive for you.

 

[rede96]

Interesting topic!

What about this scenario using gravity or acceleration to prove absolute motion. By the way, I don’t know the math on this but it still seems a good thought experiment so here goes:

Let’s say I am in a space ship, with no thrusters or power on, so all I know is that I could be traveling at some speed. So I can say that I am in an inertial reference frame.

I know that if I change direction but not speed I will still be accelerating. I also know that I will be able to measure the rate I accelerate by using something like a pendulum or some other device that would move when I accelerate.

I know the mass of my ship. So I can calculate that if I was traveling at speed ‘x’how much thrust (power) I would need to turn the ship through 90 degrees in a particular direction. I would also be able to calculate the effects of gravity (acceleration) on my pendulum.

So I execute the manoeuvre and measure the effect on my pendulum. If the pendulum swings the calculated amount I know what speed I was traveling at prior to the manoeuvre.

If the pendulum doesn’t swing the calculated amount I could then work out what speed I was moving at prior to the manoeuvre.

Therefore I can show that I was in motion (or not) without making reference to another frame.

 

[JesseM]

Let’s say I am in a space ship, with no thrusters or power on, so all I know is that I could be traveling at some speed. So I can say that I am in an inertial reference frame.

I know that there if I change direction but not speed I will still be accelerating. I also know that I will be able to measure the rate I accelerate by using something like a pendulum or some other device that would move when I accelerate.

I know the mass of my ship. So I can calculate that if I was traveling at speed ‘x’how much thrust (power) I would need to turn the ship through 90 degrees in a particular direction. I would also be able to calculate the effects of gravity (acceleration) on my pendulum.

So I execute the manoeuvre and measure the effect on my pendulum. If the pendulum swings the calculated amount I know what speed I was traveling at prior to the manoeuvre.

Why do you think it would depend in any way on your initial speed? Of course in relativity there is no objective truth about your initial speed, but different frames who define your coordinate speed differently can apply the same laws to your ship and pendulum to predict how it will behave, and all will predict the same thing for the angle the pendulum moves (not necessarily the angle in their frame, but if the pendulum string is initially lined up with the 0-degree mark on a circular protractor on board your ship, all frames predict the same thing about what mark it's lined up with at the end of the maneuver).

 

[SeventhSigma]

I don't think we can ever prove absolute space. Everything sitting still and everything moving at constant velocity V would look the same. We can only define motion in the relative sense.

 

[xxxx0xxxx]

Nay sirs,

He who accelerates has the slow clock,

the spacefarer must launch and accelerate to leave, then decelerate, turn around and accelerate to return, then decelerate to land.

The people who stay behind do not experience these effects which are general (not special) relativistic, the difference in clock times are due to general relativity.

 

[JesseM]

Nay sirs,

He who accelerates has the slow clock,

the spacefarer must launch and accelerate to leave, then decelerate, turn around and accelerate to return, then decelerate to land.

The people who stay behind do not experience these effects which are general (not special) relativistic, the difference in clock times are due to general relativity.

You're correct that if one accelerates and the other doesn't, then the one that accelerated is always the one to have aged less. However, as long as spacetime is flat (no curvature due to mass/energy) there is no need for general relativity, you can calculate the behavior of an accelerating object (including the time that elapses between two points on its worldline) just fine using an SR inertial frame.

 

[rede96]

Why do you think it would depend in any way on your initial speed?

I was thinking that if I was to use lateral thrusters, the amount of thrust I would need to turn the ship 90 degrees would depend on the speed I was travelling. The faster I was going the more thrust I need.

Something like it takes more force to change the direction of moving object then a static one, as a moving object’s mass increases. (E= mc2) the faster it goes. So if it took more force to change direction then I must have gathered more than my rest mass and thus must be ‘moving’

 

[DaveC426913]

I was thinking that if I was to use lateral thrusters, the amount of thrust I would need to turn the ship 90 degrees would depend on the speed I was travelling. The faster I was going the more thrust I need.

Something like it takes more force to change the direction of moving object then a static one, as a moving object’s mass increases. (E= mc2) the faster it goes. So if it took more force to change direction then I must have gathered more than my rest mass and thus must be ‘moving’

No. In your reference frame your mass does not increase. You are - as far as any (local) experiment can detect (including accelerating your craft in any direction) - as good as stationary.

 

[rede96]

No. In your reference frame your mass does not increase. You are - as far as any (local) experiment can detect (including accelerating your craft in any direction) - as good as stationary.

As I understood it the reason I can’t travel at c is that the energy I would need would reach infinity as my mass would keep increasing proportionately.

So I assume that mass does increase but would revert back to its rest mass once I stop accelerating. Is that correct?

 

[Mentz114]

As I understood it the reason I can’t travel at c is that the energy I would need would reach infinity as my mass would keep increasing proportionately.

This is how it would look to an observer you left behind when you started accelerating. In your frame ( spaceship ?) you would notice nothing untoward, your motors will push you along just as they did when you started. If you keep firing the engines long enough, a horizon will spring up between you and the left-behind observer.

So I assume that mass does increase but would revert back to its rest mass once I stop accelerating. Is that correct?

There's no actual mass increase, but when you stop accelerating the horizon will disappear.

Have a look at this article

http://gregegan.customer.netspace.net.au/SCIENCE/Rindler/RindlerHorizon.html

 

[DaveC426913]

In your frame ( spaceship ?) you would notice nothing untoward, your motors will push you along just as they did when you started.

Agreed. This is key.

Under your constant thrust, your pendulum would continue to stay as tilted a year from now as it does today. Again, no local experiment would indicate your velocity. (Though you could look out the window and see the galaxy passing by at .9999c.)

 

[HallsofIvy]

As I understood it the reason I can’t travel at c is that the energy I would need would reach infinity as my mass would keep increasing proportionately.

So I assume that mass does increase but would revert back to its rest mass once I stop accelerating. Is that correct?

No, you are not correct. You are missing the word "relative"- which you should constantly be using in a discussion of relativity. You cannot travel at c relative to another frame of reference because your mass relative to that frame of refererence would keep increasing. If you stop accelerating, your mass, relative to that frame of reference, would remain whatever the Lorentz transformation law for mass gives for your current speed. Your mass would "revert back to its rest mass", relative to that frame of reference only if you slowed down so you were stationary relative to that frame of reference. At any given time, you are at rest relative to yourself and so your mass, relative to yourself, will always be your rest mass.

(Any many here would argue that talking about increasing mass is out of date- your "mass" remains your rest mass while your momentum, relative to another frame of referrence increases non-linearly with speed.)

 

[Physicist1231]

Why don't you start with the results of the experiments? We have ample evidence of time dilation; Einsteinain SR and GR explain it very well. The Newtonian model does not.

Why are you trying to fix what ain't broke? What is the impetous driving your desire to find another answer when we have an answer?

Actually I am looking at a lot of experiments that have been done and the assumptions made. Some of them I do not understand why other assumptions were not made that still coincided with what was previously known.

For instance the Michelson-Morley experiment to see if aether winds existed. It was a pretty good test that showed that these "winds" that would affect a photon was affected by said winds. The verdict was that these "winds" did not exist. Why not say they just don't affect light?

Also I am still trying to find out how (and what) experiments were done that prove that Light approaches any reference point at C instead of C-V.

The emmitter theory was doomed for failure from the start because it had a bad definition as a reference point. Light is cannot be "thrown" like a ball or a bullet from a moving vehicle. Rather it is proven that light (like sound) is emitted and radiates from its original location (regardless of the new location of its moving light maker). This is why we see things like redshift and blueshift and time dilation.

(i tried to paste a picture of my understanding of this but had to make it an attachment)

Granted this is not drawn to scale but the point shows that the the distance between waves in the direction of travel is shorter so a person observing this would see the incident appear to take less time than the event actually took where as a person behind the light bulb path would see a much longer time elaps between light waves.


One other experiment I have an issue with is the Twin Paradox (started a new thread for this question). Please let me know what you guys have

 

[Physicist1231]

No, you are not correct. You are missing the word "relative"- which you should constantly be using in a discussion of relativity. You cannot travel at c relative to another frame of reference because your mass relative to that frame of refererence would keep increasing. If you stop accelerating, your mass, relative to that frame of reference, would remain whatever the Lorentz transformation law for mass gives for your current speed. Your mass would "revert back to its rest mass", relative to that frame of reference only if you slowed down so you were stationary relative to that frame of reference. At any given time, you are at rest relative to yourself and so your mass, relative to yourself, will always be your rest mass.

(Any many here would argue that talking about increasing mass is out of date- your "mass" remains your rest mass while your momentum, relative to another frame of referrence increases non-linearly with speed.)

Then now I am confused about E=mc^2... I thought that was the underlying foundation for the argument about mass needed to exceed/reach C. (and is counter acted with the guestimated size of a photon that travels at C yet any observable mass (from our reference point) is extremely minute if any)

 

[rede96]

No, you are not correct. You are missing the word "relative"- which you should constantly be using in a discussion of relativity. You cannot travel at c relative to another frame of reference because your mass relative to that frame of refererence would keep increasing. If you stop accelerating, your mass, relative to that frame of reference, would remain whatever the Lorentz transformation law for mass gives for your current speed. Your mass would "revert back to its rest mass", relative to that frame of reference only if you slowed down so you were stationary relative to that frame of reference. At any given time, you are at rest relative to yourself and so your mass, relative to yourself, will always be your rest mass.

(Any many here would argue that talking about increasing mass is out of date- your "mass" remains your rest mass while your momentum, relative to another frame of referrence increases non-linearly with speed.)

OK, Thanks.

So if I understand it, that means that even though I could start to accelerate up to 0.7c for example, stop and accelerate again at the same rate, my speed wrt to another frame of reference would keep increasing each time (as would my relative mass) but it would never reach c, and I would have to add velocities relatively.

 

[DaveC426913]

OK, Thanks.

So if I understand it, that means that even though I could start to accelerate up to 0.7c for example, stop and accelerate again at the same rate, my speed wrt to another frame of reference would keep increasing each time (as would my relative mass) but it would never reach c, and I would have to add velocities relatively.

Yes. After two successive (internal) accelerations of .7c, your velocity externally will be .94c.