is this possible?

[rune420]

Hmmm... This is just a thought i had the other day, and there must be something wrong in my reasoning, but I can't seem to figure out why this wouldn't work:

 

 

Say you had a HUGE train moving along the earth with a constant velocity of c/10 in reference to the earth. Inside this train you had a smaller train moving with a constant velocity of c/10 in reference to the larger train. Inside this you had yet another train (even smaller) moving at c/10 in reference to the small train. This train would then be moving at 3*c/10 in reference to the earth.

 

Would it not then be possible to have 11 such trains in the same way as described above where the innermost train was moving at 11*c/10 (faster than c) in reference to the earth? What am I missing?

[YT2095]

the power requirements to move your inermost train past C

and that in order to accelerate a smaller train it would be pushing backwards against the outer train (newtonian motion).

hope that helps a little

[rune420]

Hmmm... I guess you're right, there would have to be some form of push against the outer train, but what if you applied a constant force to counter this large enough for the trains to maintain a constant velocity? This should in theory be possible, right? (With massive amounts of energy, ofcourse).

 

And instead of accelerating the last train past c in reference to the earth, say you split this up into two huge (outer) trains, one with 5 and one with 6 trains, moving avay from each other (one with c/10 and the other with -c/10 in reference to earth)...

Then the innermost train would be moving faster than light in reference to the other innermost train, right? Would it still take to much energy to be even theoretically possible?

[YT2095]

without going into detail.

 

In a nutshell yes, too much energy

[rune420]

OK. I guess I'll just have to accept that then. :scratch:

 

Man, I can't wait to learn more about this stuff... I'm only a freshman, and the physics I had in (the norwegian equivalent to) high school were mostly classic mechanics (not relativity or QM at all)...

[YT2095]

Well no one was BORN knowing this stuff, so don`t feel bad

it will involve plenty of work sure, but if you`re interested, you`ll find most of it quite interesting, and dare I say it "Enjoyable".

Stick around, there`s a good many on here that usualy come on later, that will give you even more help. just having to "accept it" wouldn`t/shouldn`t be good enough for you, see what the others say about it also

[VendingMenace]

perhaps a simpler example of what you are asking is the following...

 

you have one spaceship traveling at 0.6c. Another spaceship is traveling in the opposite direction, directly towards the first ship, also at a speed of 0.6c. Wouldn't the speed of one ship, as observed from the other ship, be 1.2c?

 

I think this is the jist of what you are asking. Also, this gets us away from questions of energy and deals soley with the speed of light.

 

The quick answer to this question must consider two types of observers...

 

1) An observer in a fram of rest (outside the ships and not moving) see two ships that are flying towards eachother, each at 0.6c, closing the distance as a rate that is 1.2c. However, this is not a problem, since neither of the ships is individually going faster than the speed of light. So, in a frame of rest, we see that the are not going faster than c.

 

2) This is the tricky one. For an observer inside either of the space ships, he does not observe the other spaceship approaching at 1.2c, rather he obsevers the other spaceship closing at some speed less than c. Crazy!

 

the reason for this is the time-dialation effect and length contraction effects of travel near the speed of light. Unfortuanately, i do not have a physics book with these equations in them here at work, so i cannot give you the mathmatical explination right now. However, perhaps when i get home, whenever that will be

[rune420]

Thanks, that was just what I was wondering about! I guess I should read up on time dilation a little more... Seems like interesting/mind-bending stuff!

 

I'll definately keep visiting this forum!

[VendingMenace]

ok, back from work. so yeah, you will have to do some reading, but i will try to explain as best i can here...

 

when calculating velocities in special relativity we must take into account both time dialation and length contraction. That is, time moves slower for a person the faster his speed, and things that are moving fast are shorter then when they are at rest. Given these consequences, we can take both and write ourselves an equation for relative velocities.

 

the equation that will be of use is the following (i am not going to show its derivation, as it would take a bit too long due to the fact that i would have to show the derivations for time dialation and lengthcontraction as well)

 

u' = (u-v)/[1-uv/(c^2)]

 

where;

u' = the velocity of the object being observed, in the frame of the observer

u = the velocity of the object being observed from a rest frame

v = the velocity of the observer

c = speed of light

 

cool, so all that remains is to plug and chug...

the velocity of the observer is 0.6c (this is the velocity of the spaceship from wich you are doing the observing)

the velocity of the object is -0.6c (this is the other spaceship that is traveling 0.6c in the opposite direction from you)

 

 

great so then we get...

 

u' = [(-0.6c) - (0.6c)]/[1 - (-0.6c)(0.6c)/(c^2)]

 

u' = -0.882c

 

thus, we see that, for two ships headed towards eachother, each with a speed of 0.6c, a person on one of the ships will observe the other ship approaching at 0.882c, even though a person at reast will observe them closing distance with an effective speed of 1.2c!

 

this is a direct consequence of the fact that nothing goes faster than the speed of light, and indeed for this example, we find that for the case of an observer on a ship or for one at rest, nothing is found to be going faster than the speed of light.

 

hope that helps somewhat, like i said earlier though, you will have to read some to really get what is happening, but i am sure that if you continue to take physics you will get there

[iglak]

VendingMenace said in post #7 :

the reason for this is the time-dialation effect and length contraction effects of travel near the speed of light. Unfortuanately,

is that the reason? or is it just that light always travels the speed of light (or slower in a medium), so it takes time for light to travel that distance?

 

YT2095 said

In a nutshell yes, too much energy

yes, too much energy, but it is supposedly not a finite amount of energy.

 

as things gain speed, they actually gain mass (called "relative mass," but acts the same as normal mass)

so, the closer the trains get to the speed of light, the more energy is required to increase the speed of the increasing mass.

 

 

 

although, this could just be because of something else (a theory of mine) that i can only describe through an example:

-let's say we have a perfectly spherical planet made completely out of evenly spaced... alluminum molecules(any solid will do).

-lets say we have another perfect phere made out of the same material about the size of a boulder.

-now, lets say we have ten silos full of ball bearings (bb's).

-connected to these silos, with an automatic feed, is a rapid fire, automatic gun that always shoots these bb's at exactly 100mph, and any rate of bb's/second

-now that all of the specifics are done, we fire these bb's at the boulder.

-no matter how many we fire at the boulder, and no matter how many we fire per second, the boulder can never be propelled faster than 100mph. even if it could, the bb's wouldn't be able to hit them to move it any faster...

 

now, if nothing can travel faster than the speed of light, how will we ever find something that can to propell our faster-than-light travel? could this be the increase in mass as things approach the speed of light? if not, what could be it?

 

 

P.S. can gravity an magnetism travel faster than light?

 

P.P.S. did i get anything wrong if you know?

[rune420]

Originally posted by iglak

although, this could just be because of something else (a theory of mine) that i can only describe through an example:

-let's say we have a perfectly spherical planet made completely out of evenly spaced... alluminum molecules(any solid will do).

-lets say we have another perfect phere made out of the same material about the size of a boulder.

-now, lets say we have ten silos full of ball bearings (bb's).

-connected to these silos, with an automatic feed, is a rapid fire, automatic gun that always shoots these bb's at exactly 100mph, and any rate of bb's/second

-now that all of the specifics are done, we fire these bb's at the boulder.

-no matter how many we fire at the boulder, and no matter how many we fire per second, the boulder can never be propelled faster than 100mph. even if it could, the bb's wouldn't be able to hit them to move it any faster...

 

now, if nothing can travel faster than the speed of light, how will we ever find something that can to propell our faster-than-light travel? could this be the increase in mass as things approach the speed of light? if not, what could be it?

 

Hmmm... What if you put the gun on the boulder instead? The recoil of the gun would then accelerate the velocity of the boulder (assuming vacuum, and that the gun is positioned in such a way that it would not tilt the boulder [easier if you picture it in free space i guess]) so that you could propell the boulder beyond 100 mph, right?

Yet as far as I can see you could still never reach light-speed as a result of the lorentz-transformations (out of curiosity I read a little today, though it's not really part of the classes I'm taking right now).

[VendingMenace]

is that the reason? or is it just that light always travels the speed of light (or slower in a medium), so it takes time for light to travel that distance?

 

No. The reason is a combination of time dialation effects and length contraction effects. THis is easily seen. Velocity defined as a change in distance over and change in time. That is, if you travel 6m in 12 sec, then we say that your average velocity was 0.5m/s. Thus, when we talk about relativistic velocities, we much take into considerate how reletavistic speeds effect both distance and time. In special relativity, we find that as one appraoches the speed of light, one experiences both time dialation and length contraction. Thus, considerations of velocity MUST take into account (and if fact, rely on) these effects.

 

I apologize for the curtness of this response. Perhaps it seems a little unsatisfying, but as a said earlier it would take awhile (at least serveral pages) to explain this adequately. Perhaps i will write a short paper on it someday that can be posted on this site, but for now i fear you must decide to trust me or not.

 

 

did i get anything wrong if you know?

 

yuppers, you got some stuff wrong. Good thinking though, it is cool that you are thinking about this stuff.

 

Here is where you went wrong...

 

Lets assume that the bb's you are shooting at the boulder have a mass of 10kg. Lets also assume (for the sake of argument) that the boulder has a mass of 1kg. Now, we will be generous and assume that durring the course of the collision, all the enrgy in the bb is transfered to the boulder. Also, the bb does not stick to hte boulder.

 

OK, so, in the beggining, we have a bb that wieghs 10kg and is traveling at 100m/s (i know that you had 100mph before, but m/s is easier to work with). WE can then calculate the energy of hte bb. Specifically;

 

Energy of bb = (mass of bb)(velocity of bb)^2

= (100kg)(100m/s)^2

= 1 X 10^6 Joules

 

ok, then the bb hits the boulder, right? WEll, energy must be conserved, and we know that all the energy from the bb goes into the boulder, so we have

 

energy of boulder = energy of bb = (mass of boulder)(velocity of boulder)^2

 

1 X 10^6 Joules = (1kg)(velocity of boulder)^2

 

veclocity of boulder = [(1 X 10^6 Joules)/(1kg)]^(1/2)

velocity of boulder = 1000 m/s

 

Thus, we see that in this case, ONE bb was able to accelerate the boulder to 10 times the speed of the bb. THerefore, it is possible for the bb's to propell the boulder faster than the bbs themselves were going.

 

Perhaps you think that i changed the problem by making the bbs more massive than the boulder, but not really. All i did was simplify it. In the end, if hte boulder was more massive than the bbs, then the bbs would incrimentally increase the energy of the boulder until the last bb that could possibly strike it would. At this time, the boulder would have either the exact same speed as the bbs, or just a bit more speed than the bbs, depending on how the problem is set up.

 

Anyways, the point being that, yes, it is possible for hte bbs to propell the boulder faster than the bbs themselves are traveling.

 

 

can gravity an magnetism travel faster than light?

 

No, magnetic waves and the effects of gravity both propogate at the speed of light.

 

WEll, i hope that answers your questions, feel free to ask more

[iglak]

hmm...

so a bb with more mass than the boulder would knock the boulder faster than the bb was traveling... so ALL of the kinetic energy must be transfered to the boulder (minus friction)

 

wait... if this were to happen, wouldn't the boulder be knocked at 100mph, and the bb would just slow down a little from the impact? wouldn't the bb transfer only the energy needed to push the boulder 100mph, and keep the rest to sustain it's own movement?

 

[rune420]

Originally posted by iglak

wouldn't the bb transfer only the energy needed to push the boulder 100mph, and keep the rest to sustain it's movement?

 

No, he stipulated that the bb lost all its energy thus all it's velocity in the collision. Ofcourse, this would most propably not be the case in reality.

[VendingMenace]

wait... if this were to happen, wouldn't the boulder be knocked at 100mph, and the bb would just slow down a little from the impact? wouldn't the bb transfer only the energy needed to push the boulder 100mph, and keep the rest to sustain it's movement?

 

But how would the bb know how much to transfer? The bb is has no idea how much energy the boulder currently might have, so there is no way for it to transfer "just enough."

 

so ALL of the kinetic energy must be transfered to the boulder (minus friction)

 

well, in the example i provided i assumed the bb would transfer all of it energy. Of course this may not be the case. It the bb transfers ALL of its energy, the we find that it stops after the collision, and only the boulder is moving. Another possibility is that the bb bounces backwards after impact, (like a steel ball bearing does if you drop in on the ground). IN this case not only did the bb transfer all of the energy into the boulder, but it gave the boulder EVEN MORE energy than it had. That is becuase it gave all the enrgy it needed to stop, but then it headed in the opposite direction. Thus, in order to preserve conservation of momnetum, the boulder must also gain a bit more velocity than it would have otherwise and hence it would be going FASTER than in my original anylisis. HOwever, Perhaps the bb only transfers some and keeps some, but moves at a reduced velocity as you suggested. IN this case it is true that the boulder would be traveling slower than in my example, but if it was traveling slower than the bbs, then another bb would just strike it, transfering more energy to the boulder, and now we are back to the same exact situation. That is, after a certain number of collisions, the boulder will either be traveleling the same speed as the stream of bbs (very very unlikely, one case in an infinite amount of cases) faster than the stream (most likely).

 

Does this make sense? Fell free to keep asking questions

[iglak]

but, if there were no variables effecting speed other than the bbs, then if we shot these bbs at the boulder, wouldn't the boulder not be able to reach 100mph? the faster the boulder goes, the less effect the bbs have on it, because the slower the bbs are going in realation to it, and the less energy they transfer on impact. thus, it will take infinite bbs to push the boulder 100mph, a.k.a. infinite energy.

 

and back to the big bb, inertia causes it to lose as little kinetic energy as possible, but since the boulder is directly in it's way, the only way to keep kinetic energy is to transfer enough energy to keep the boulder ahead of it

 

 

and about the person seeing the ship coming in at a certain rate... the person will actually probably see the ship closing at abou 1.2c. since time dialation is ture, it takes more for movement to happen. people see at 30 frames/second. the faster you travel, the slower time is for you. you'd still percieve it as normal speed, because you frame rate will decrease with the decreasing time rate, and your movement speed will decrease with the decreasing time rate.

 

so, the closer you get to the speed of light, the closer you get to infinitely fast, from your perspective... MUAHAHAHAHAHA!!!

[VendingMenace]

the faster the boulder goes, the less effect the bbs have on it, because the slower the bbs are going in realation to it, and the less energy they transfer on impact.

 

Sure, this is true. But they still transfer a discrete amount of energy per impact. And you will find that, at one point in time, the total amound of energy transfered will be enough to make the boulder go faster than 100mph. Of course since the bbs are small and the boulder is big, it will not be moving much faster than 100 mph. It might even be moving faster by so little that you would not be able to tell without the aid of some very good equipment. That is why i choose the example of the large bbs and small boulder. The same priciples hold. Thus, the same conclusions hold. The stream of bbs can push the boulder fast then they themselve go.

 

and back to the big bb, inertia causes it to lose as little kinetic energy as possible

 

This is not true.

INertia causes no such thing. All that inertia is, is this. Inertia means that objects in motion tend to stay in motion, and objects at rest tend to stay at rest. Unless they are acted upon by some net force. Nowhere does it state that objects will loose as little kenetic energy as possible.

 

the only way to keep kinetic energy is to transfer enough energy to keep the boulder ahead of it

 

again, you are mistaken. THink about when you play billiards. When the cue ball strikes another ball, does it transfer just enough energy to keep the billiard ball ahead of it? Not really. Objects do not "know" what is in their way. They do not "know" how much energy to transfer in order to keep things ahead of them. Thinking in this way is just asking for trouble.

 

the person will actually probably see the ship closing at abou 1.2c.

 

well, you are absolutely inccorect here. I dont really know how else to say it :/

 

since time dialation is ture, it takes more for movement to happen. people see at 30 frames/second. the faster you travel, the slower time is for you. you'd still percieve it as normal speed, because you frame rate will decrease with the decreasing time rate, and your movement speed will decrease with the decreasing time rate.

 

so, the closer you get to the speed of light, the closer you get to infinitely fast, from your perspective... MUAHAHAHAHAHA!!!

 

i think it is obvious that you have not taken reletivity. it is equally obvious that i will be unable to just glaze over the effects of special relativity. Sadly, i am not sure i have the time to organize a consise, yet complete treatment of hte subject for this thread. You will just have to decide whether or not you belive me in this case. If you want any sort of reference, i used the equations out ofNonclassical Physics: Beyond Newton's View by Randy Harris. It is a college text about nonclassical physics wich give a fairly detailed treatement of special relativity and a rather cursory look at other topics like GR, QM, and stat mech.

 

I hope i do not sound condesending, i do not mean to. I think it is great that you are asking questions, but at the same time i will correct you where you are wrong.

[iglak]

The stream of bbs can push the boulder fast then they themselve go.

i am hesitant to trust you on this one. i wish i had some precise equiptment to test it...

Objects do not "know" what is in their way. They do not "know" how much energy to transfer in order to keep things ahead of them.

who said they "know" anything? not me. they don't have to "know" something for it to happen.

When the cue ball strikes another ball, does it transfer just enough energy to keep the billiard ball ahead of it? Not really.

i just looked it up on a few sites, your right. if the cue ball hits another ball dead on, it transfers all of the energy to it. so that means you're probably right about the other bb stuff. since this was kind of the basis of it all.

i think it is obvious that you have not taken reletivity

i definitely have not, i am still a junior in high school...

 

but, if time slowes down to a moving object at near-light speeds, relative to a stationary object, then the moving object would observe themselves going faster than the speed of light.

 

lets say i want to travel 10 light years at... 0.9c. since my time slows down during that travel, only a few years would pass for me while more that 10 would pass on earth. if i traveled those 10 light years in only a few years, relative to me, then shouldn't i observe the outside world passing by faster than the speed of light? why would it be otherwise?

 

ohh!!!!! never mind. i get it, the length appears to contract, the planets, stars, whatever would appear extremely thin, and they would be moving 0.9c relative to me... i get it now (i hope).

 

 

P.S. i found this site, an easy to understand, basic explanation of this type of thing.

[Kedas]

YT2095 said in post #6 :

Well no one was BORN knowing this stuff, so don`t feel bad

 

This obvious rises the question: WHO told Einstein??

[swansont]

iglak said in post #18 :

i just looked it up on a few sites, your right. if the cue ball hits another ball dead on, it transfers all of the energy to it.

 

That's because the objects have equal masses and the collision is pretty much elastic, so KE is a conserved quantity along with momentum.

 

If the collision isn't head-on, or the masses are unequal, the conservation laws dictate that the projectile will retain some KE. Under some circumstances, it can end up with more than it started with (target moving toward projectile).

[VendingMenace]

sorry sorry sorry, i seem to have posted here by accident, and i don't have permision to delet this. could some admin type please delete me? Thanks, and sorry

[YT2095]

LOL @ Kedas

he worked it out for himself (but you know that). another good reason Rune420 shouldn`t give up!

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