/sci/ - Science & Math

>>4980135
photons basically stand still in time

photons don't have a frame of reference.

>>4980135
Actually in each photon's reference frame, the other is moving away at C. At 2C that does violate relativity

time dilation, both photons are moving c related to each other.

>>4980135
The both photons will see each other standing still.

photons don't have eyes silly op

>>4980145
this
Simplistically: if you "boost" to a the reference frame of a photon, it has zero energy.

Also
http://en.wikipedia.org/wiki/Velocity-addition_formula#Special_theory_of_relativity

Velocities never add to above the speed of light.

>two photons move in opposite directions, both at C
>each photon sees the other receding at C
My mind seriously can't comprehend how this is possible.

How can the distance between the two photons be growing at 2C, yet the photon 'sees' that distance growing at 1C?

>>4980190
it doesnt work with photons, but asuming its 2 rockets going at 0.999999 the speed of light, then they will she the distance grow by less than c becasue time will slow down for them to the point that it seems like its growing at 0.99999c instead of 1.99999998c.

>>4980196
That was a good explanation, thanks.

The universe repeats itself.

So they the photons will eventually pass throu each other which of course cancel's da 2C.

>>4980135

It doesn't violate relativity because your statement is wrong.

If you do the same thing with 3 photons, they have a relative velocity of 3c

>>4980163
This absolutely.
/thread

>>4980145
>>4980135
>photon's reference frame

Photon's do have reference frame but they are funky. In them, time has stop and both the starting point and end point are at the same exact location.

>>4980219
>not sure if trolling or really stupid.

>>4980328
Really you can't tell if that he is trolling?
Protip: Good grammar means above average intelligence.

look OP, you are right, it's just that humans haven't achieved the speed of light to test your theory.
Ask /sci/ about this and they tell you "it doesn't add above the speed of light " just as christians say "the bible says so"

>>4980358
>can't tell if that he is trolling?
>if that he
>Good grammar means above average intelligence
i'd disagree, but if you say so. also, poe's law.

>>4980371
I said intelligence, not sanity.

>>4980196

So actually, its not that its impossible to reach 1C, its that it would be impossible to reach 0.5C.

Since the measure is "per second" then for only seeing the other object at 1C maximum, it must be the case neither object can exceed 0.5C in their frames of reference.

>>4980454
Not really.....to reach 1C would require infinite energy.

>>4980468
>>4980454
Disregard these two posts. They are talking out their asses

>>4980454

No, it's impossible to reach C because at relativistic speeds, velocities do not add. Only a percentage of the velocity is added, and that percentage goes down immensely the closer to C you get, to the point where you need more energy than exists in the universe just to go another 1/ms closer to C.

Particle 1 is traveling at 0.1C.

Particle 2 is released from particle 1 at 0.1C

Subsequent particles are released from each particle at a velocity of 0.1C.

By the 21st Particle the relative speed of 1st and 21st particles is 2C. But between each particle, no law has been voilated with a relative difference in velocity of 0.1C.

What now?

>>4980480

They don't add, genius. The particle is always going the speed of light relative to the other particle.

Fucking god, are people really so stupid that they think a small-world thought experiment can trump Relativity?

You people are worse than christians.

>>4980473
So you're going to claim >>4980477 is a shit post too even though it's the same thing I said here? >>4980468

The limit tends to infinity* if you're trying to be stingy about my grammar.

>>4980485
A better display would to show the relativistic formula and explain why "they don't add" (which is a shit expression to begin with), rather than straight name calling.

Even though I agree, they should do the research themselves to earn their spot in the Intelligencia

>>4980489

Well he explained why you need infinite energy, you simply stated that it does.

You need to coddle people who don't understand or don't trust science. You can't reinforce their beliefs by not stating the reasons behind phenomena.

>>4980498
Is it not on the inquisitive to do a little background research before asking a question? This whole debacle seems like something that could be easily resolved with a high school textbook.

>>4980495

I sincerely doubt they'll be able to read it, but whatever.

>>4980502

They don't teach relativity in high school.

I agree that they should do the research, but let's be realistic. How many normal people closely examine their beliefs?

>>4980504

Note that in special relativity, velocities do not add. Instead, rapidities add. The velocity is the speed of light times the hyperbolic tangent of the rapidity. At low rapidities, the rapidity times the speed of light is almost the same as the velocity. However, no matter how high your rapidity gets, the hyperbolic tangent maxes out at 1 for very large rapidities so that your velocity can never be higher than the speed of light.

So imagine someone in a starship. As he burns propellant, the (delta-V) / (c) consumed adds to his rapidity. If he has a lot of delta-V, he can get a very high rapidity, but when you look at the velocity, it is always less than the speed of light.

Interestingly, the time dilation and length contraction factor is the hyperbolic cosine of the rapidity.

>>4980507
Then should they expect us to put in more effort to explain a concept to them when they don't match that effort beforehand? It seems rude to me.

>>4980523

It is. But that's how stupid people are. They think that the entire universe can be explained to a dumb monkey that barely learned to throw a spear before it went to the moon.

>>4980485

I'm not exaclty trying to trump relativity, I am trying to get an explanation whats going on here. Also

>The particle is always going the speed of light relative to the other particle.

You obviously did not read my post properly if you made this statement.

>>4980504

This only defines speed of light as an absolute limit if there is an absolute reference frame through which to label velocities. Far as I am aware, there is no such thing as an absolute reference frame.

If we reduce the particles to 19, and call particle 10 the ultimate reference frame. no single particle has exceeded a velocity of 1C, and has therefore not aquired infinity energy.... but if particle 1 were the reference, particle 19 cannot be at its current velocity.

>>4980537

>This only defines speed of light as an absolute limit if there is an absolute reference frame through which to label velocities. Far as I am aware, there is no such thing as an absolute reference frame.

If you don't understand the maths, then why are you arguing?

In SR the degenerate case of "a photon's frame of reference" is a static 2-dimensional universe where time doesn't pass and nothing moves.

>>4980537

>You obviously did not read my post properly if you made this statement.

Your example is flawed. You're making the argument that a FTL starship that turns on it's highbeams will therefore have highbeams going out at 2x the speed of light, when in reality the light beams are only going C relative to the ship.

The light beams, no matter how many particle whatevers you add, will always be going at no more and no less than C.

If this confuses you it is because mankind had no reason to evolve the mental faculties required to understand relativity. It's why we use maths to describe it in fine detail.

>>4980543

>implying understanding of the math

Go ahead, explain it to me.

>>4980551

Read this. >>4980511

>>4980511

>The velocity is the speed of light times the hyperbolic tangent of the rapidity

aaand i'm lost.

So it's magic? I can understand that.

>>4980550

You're breaking my example down into photons again. That isn't my point here.

My point is where is the frame of reference through which a velocity is truely decided. Is it through the nearest gravitational body of influence for example?

if a spaceship is in space, its velocity at this stage, we will say is immaterial - and it launches a ship at 0.1C relative, then that ship launches another at 0.1C relative....

do you understand the example now? I did not at ANY point explicitly mention photons at all. no object here is going the speed of light relative to the object it has left in the example.

>>4980565

Then when the ship that is traveling at some large fraction of C goes to launch a ship, it finds that it does not have enough energy to thrust any faster than the ship behind it.

Because velocities DO NOT ADD. It's not like where if you shoot a gun out of a moving car the bullet is going supersonic +60mph. You keep dragging Newton into Relativity.

>>4980565

Do you not realize that minds far greater than yours have been tackling this problem for the last hundred years and not one of them has been able to find a workaround?

Do you not realize how many times your example has been refuted in history?

>>4980555

This doesn't explain the concept of rapidity. Also, "DeltaV" over (C) doesn't make a lot of sense here. DeltaV is a measure of the capacity of an object to change its speed through the mass fraction and ISP. Which yes, I guess can never reach C ... for a single stage. When talking multiple stages, this limit begins to break down. Even though the first stage is impractically large.

>>4980573

>This doesn't explain the concept of rapidity

Well then take a goddamned GR course you stupid fuck.

I'm not teaching you a crash course in advanced physics just because you're too lazy to learn it yourself. I've tried my absolute best to explain it to you, but you keep arguing from pure ignorance.

First, photons do not have reference frames. They do not have a rest frame thanks to gauge invariance.

Secondly, the Minkowski metric says <span class="math">c[/spoiler] remains constant in every reference frame. There is no 2*c.

/thread

Let me blow your mind.

Going by the distance you measure before your journey and the velocity you calculate you'll reach relative to your "stationary" position before you start accelerating, you'll perceive yourself to be travelling at (v/c)/sqrt(1-(v/c)^2).

Notice that despite it being "impossible to exceed the speed of light", you can actually travel at any speed you want, from your own perspective. You can travel a million light years in a minute, it's just that you also time travel a million years into the future.

The other way they say this is that the universe squashes to make your trip shorter, so you go flying by a lot of pancake-shaped stars, and you make the universe lopside-aged so it's older in front of you and younger behind you, but let's be realistic: that's not how you'd think about the trip if you took one.

>>4980610

Only a lifetime of watching the science channel could provoke such a confusion of ideas.

>>4980614
Go fuck yourself. There's nothing wrong with what I said.

>>4980616

Nothing with a rest mass can exceed a velocity greater than C.

It seems you've confused time dilation with some weird aspect of frame dragging. Like i said, i cannot comprehend the confusion of ideas that would even lead to such a statement.

>>4980620
>Nothing with a rest mass can exceed a velocity greater than C.
So the problem here is that you can't read.

I explicitly said that you weren't going to exceed a velocity greater than the speed of light. From the frame of reference of the pre-acceleration spacecraft, you would be travelling at v. From the frame of reference of the full speed spacecraft, you would not be travelling at all.

However, in terms of subjective experience, you would look at the distance you travelled, look at your watch, and say, "Hey, I just went (v/c)/sqrt(1-(v/c)^2)!" which can exceed the speed of light or any other finite speed.

>>4980634

That's not how time dilation works, and again this would only work if the ship was traveling at C, which is impossible.

>>4980576

You're the one spouting insults here and incorrectly referencing my statements, assuming it is you who made previous posts.

You do need to remember that science and engineering is based upon the learning of others, and what knowledge is passed down from them that others learn. Just spouting Ignorance at people and explaining nothing, proves nothing. It does not prove you are of any greater intelligence. It also proves you do not have an understanding of the bigger picture here, which is very ironic considering you seem to be into your general relativity…which considering your attitude - I actually doubt.

I'm really wondering now how many people on /sci/ just copy paste wikipedia articles, as that seems to be the impression I am getting. Disapointing.

>>4980637
It's exactly how time dilation works. With sufficient (sublight) velocity, you can experience an arbitrarily small amount of aging while travelling any arbitrarily large distance.

the reasone from frame of reference it looks as 2C because the speed of the one being viewed is added to the one moving away =2C

>>4980645

Except they don't add.

>>4980638

Dude, don't be a little cunt. I did tell you how to expand your knowledge. Take a course in GR. Do you honestly expect me to teach all of it to you, lest I be the jerk?

>>4980641

You're still not going any faster than the speed of light.

so your saying that 2 cars traveling in different directions one at 20KM other at 50KM don't =80Km from the reference of eaither car? same thing here but with photons

exactly the speed of each photon stays at speed of light.

>>4980661

That only works in relatively slow speeds.

It does not apply in relativistic speeds.

>>4980641

quick quiz, hotshot, which reference frame is moving at slow motion? Terra to the ship, or the ship to Terra?

>>4980573
Rapidity is just a fancy name they give to <span class="math">\frac{v}{c}[/spoiler], for our purposes. With GR, there's also shit to do with hyperbolic trigonometric functions where it comes into play.

awsome quiz, each photon is at same speed not complete different.

>>4980674
Rapidity is <span class="math">\tanh^{-1}(v/c)[/spoiler]. It's the spacetime version of angle whereas velocity is the spacetime version of slope.

>this thread

>>4980653

I am expanding my knowledge. I'm already doing a Masters in a specialist field of engineering. So obviously, I don't have the time to do a General Relativity course.

All I asked you to do was offer an explanation in relation to the example I gave you, which you have failed to do so.

Christ I dunno why I'm wasting time on you, I have a thesis to finish. You're blatently a wikiwhore. I'll admit I only know base level physics and calculus. (about all you need to be an engineer to be honest) But its better than being a know-it-all douchebag, who in truth knows nothing.

How about you expand your knowledge? Or at least, if you are as knowledgable as you claim to be, actually be humble about it and try to inspire people.

So say i'm moving at C and passing a bunch of stars... What do the stars look like? Compressed into a sheet? Moving or standing still?

>>4980710

hey, can you teach me maxwells equations?

I don't know anything past basic calculus, but i've always wanted to learn.

Also, how do magnets work? Again, as non mathematical as possible.

Thanks!

>>4980659
In what sense?

In the familiar sense of a traveller's subjective perception of distance and duration of a journey, then yes, you're exceeding the speed of light. You know at the start that your destination is a million light years away, you zip over there in what feels like a minute, you look at your watch and only a minute has passed, you say, "I just travelled a million light years in a minute!"

True, a million years (and a little bit extra, I'm talking round numbers) has passed at your departure point and at your destination, but you didn't notice any million years passing. From your perspective, you just travelled time a million years into the future.

From the scientific definition of speed used for special relativity, you never exceeded the speed of light in any frame of reference, and yet by a common-sense understanding of "speed" you subjectively perceived your journey to be accomplished at a speed vastly exceeding the speed of light.

Is one inherently more valid than the other when describing the practical consequences of special relativity in plain English?

To say that nothing can travel faster than the speed of light is no more illuminating than to say that all objects are stationary in their frames of reference. One could as well say that it is impossible to travel, one can only change reference frames. These statements can be seen as true, in a narrow technical sense, but are not helpful to the layman.

the photons will never "see" each other. the information from one photon will never reach the other

>>4980714

You don't see them. You're moving too fast for their light.

>>4980710

>not learning GR so you can engineer time machines and wormholes

ISHYEDDT

>>4980725

>True, a million years (and a little bit extra, I'm talking round numbers) has passed at your departure point and at your destination, but you didn't notice any million years passing. From your perspective, you just travelled time a million years into the future.

Time dilation is nowhere near this severe. Even at 99% of C 24 hours on the ship is just 24.12 hours in a stationary reference frame.

A million light years is still a million years for the occupants of the ship.

>>4980668
>quick quiz, hotshot, which reference frame is moving at slow motion? Terra to the ship, or the ship to Terra?
Both to each other. However, you must take into account the time skew inherent in switching reference frames, which is what makes everything at your destination so ancient on your arrival (the "time travelling" effect I previously mentioned).

>>4980747

Took you long enough to look it up on wikipedia.

You're still wrong though, because time dilation is hardly noticeable at any speed less than C.

>>4980736
>Time dilation is nowhere near this severe.
>Even at 99% of C
You lack imagination. There is no limit on time dilation.

It may prove impractical to accelerate yourself to such a velocity that you get from one galaxy to another in a perceived minute, but there's no fundamental theoretical obstacle.

>>4980752
>Took you long enough to look it up on wikipedia.
Now that's just being childish. I was obviously busy writing the long reply here: >>4980725

>time dilation is hardly noticeable at any speed less than C.
...and this is just being pathetically ignorant. Time dilation would be infinite at C.

This debate revolves around perception. We cannot perceive anything traveling faster than light so we say it cannot be possible

this is our flaw

we are limited by our own perception

Time itself is a flawed perception.

>>4980730

>implying I intend to work on wormholes?

I dunno where this is supposed to have came from.

>>4980724

A fair relation perhaps to what I am asking you, but you could at least describe the effects. Say "put a magnet near another magnet, how will will they behave relative to one another?" That can be done qaulitively. why can you not do that with particles relative to one another in GR?

>>4980757

good thing i said LESS THAN C, huh?

>>4980754

t = t_o/sqrt(1-v^2/c^2) |
t | time seen by stationary observer
t_o | time in rest frame
v | velocity
c | speed of light in vacuum (~~ 2.998×10^8 m/s)

So if T0 is 86400 (one day in seconds) then what do you get when you solve for T?

>>4980770

How about: Why does aligning the electrons in a metal cause it to extend the normal electromagnetic resistance out to a visible scale?

>>4980773
I'm sorry, you're just too stupid to talk to.

I didn't agree or disagree with your calculation of time dilation at 99% of c. It's a waste of time to check the figures, because it's an irrelevant objection.

The fact of the matter is that we aren't theoretically limited to 99% of c. At least in theory, we can go 99.9% of c, or (1-1/(10^10^10^10))c. For any amount of time dilation you want, there is some theoretically allowable velocity that provides it.

>>4980803

>The fact of the matter is that we aren't theoretically limited to 99% of c

Yeah, theoretically we'll be lucky if we can ever make an engine that can go 25% of C.

>>4980803
99% of c
99.9% of c
99.99999999% of c
99.999999999999999999999% of c
99.9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
99% of c

<div class="math">\rlap { \lower{-1.5em}{You ~can't~ travel }} \rlap { \lower{-1.9em}{Cant}} \rlap { \lower{-2.5em}{~~~~~~~~can't ~travel~ the~ speed}} \rlap { \lower{0.6em}{of~ light}} \rlap { \lower{0.5em}{of ~~light}} \rlap { \lower{1.9em}{only~ a~ fraction}} \rlap { \lower{2.5em}{~~~~~fraction }} \rlap { \lower{2.7em}{~~~~~~fraction }} \rlap { \lower{3.4em}{~~~~~~~~~~~~~~~~~0.999^{9^{9^{9^{9^{9^{9^{9^{9^{9^{9^{9^{9^{9}}}}}}}}}}}}}}} \rlap { \lower{3.5em}{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=1}} \rlap { \lower{3.4em}{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=1}} \rlap { \lower{4.2em}{you~ can ~travel ~at ~the ~speed ~of ~light}} \rlap { \lower{4.25em}{you~ can ~travel ~at ~the ~speed ~of ~light}} \rlap { \lower{4.1em}{you~ can ~travel ~at ~the ~speed ~of ~light}} \rlap { \lower{4.7em}{you~ can ~travel ~at ~the ~speed ~of ~light}}</div>

>>4980810
>theoretically

>>4980810
>Theoretically
>not practically

>>4980820

Practically we'll be lucky if we can get 5% of C.

so, what about this CERN thing guys?

I heard they do good relativity

>>4980823
>>4980810
what the fuck?
we've had designs for a starship that can get to 20% the speed of light in 2 years since the 1970s using tec from the time. and now we cant even with future tec get to 25%? wtf?

>>4980823

British Interplanetary Society, Project Daedalus.

0.1C

>>4980838

The secret is that he doesn't know what he's talking about.

>>4980810

if we set the phasers to the resonant frequency of the dilithium crystals we could boost the power output to the warp drive and achieve light factor .99 for a limited time captain and race our photon torpedoes. But I canne make any promises captain!

>>4980838
Actually we had a design of a 50%c starship back in the 50's. Look up project ORION.

>>4980887

That definately doesn't sound right. I'm sure orion was only intended to go to Mars maximum with a huge payload.

General relativity is a theory about gravitation. It has nothing to do with OP's question, and you don't need it to understand rapidity.

>>4980135
No such thing as a reference frame at c.
Speeds don't add in relativity - non-Euclidean geometry and all.

>>4980914

Special relativity however has everything to do with OP's question, so I'm not sure what your getting at.

>>4980610
Anyway, this was an introduction to the concept called "proper velocity" or "celerity".

In relativity, there are four different sorts of velocity or speed which are each useful in their own way:

"Coordinate velocity" (commonly called "velocity") describes how quickly an object passes through space as measured by a stationary observer. It's what makes sense when you try to figure out what time it will be when you get to your destination.

"Proper velocity" (sometimes called "celerity") describes how quickly a traveller passes through space as measured according to a stationary map but by his own moving watch. It's what makes sense when you describe your experience of setting a route, travelling at a constant speed, and measuring duration.

"Rapidity" describes the speed resulting from the sum of accelerations experienced by an initially stationary traveller. It's what you accumulate steadily as you accelerate at a comfortable constant 1g with your magic future rocket.

"Lorentz factor" describes how fast something is moving in terms of how much relativistic weirdness is happening to it.

Aside from Lorentz factor, each of these quasi-speeds matches the classical, common-sense understanding of velocity or speed in one way, but is a mismatch in other ways. Of the four, only coordinate velocity has any limit.

>>4980932
There was some faggot in the thread telling OP he needed to take a GR course.

>>4980911
There were Orion designs for interstellar travel, but I think they were limited to about 0.1 c.

Orion would have good acceleration and was fuel-efficient enough to jet around the solar system nicely, but a fission fragment rocket gets significantly more delta-V out of a given mass of fuel.

>>4980934
I learnt rapidity as being the pseudo-angle of "rotation" for the Lorentz matrix. Is this the same quantity?

>>4980957
Yes.

>>4980911
>>4980949
Super ORION was designed for interstellar travel at 50%c with 3000000t useful load and 5000000t of fuel and spaceship itself.

>>4980962
(and the "constant 1g" is subjective acceleration, what you'd feel as a passenger on a rocket ship gaining rapidity at a rate constant to your perceived time)

>>4980965
The only Orion I heard of that was supposed to reach 0.5 c was a theoretical antimatter bomb version.

>>4980982
I've checked it and you're right, I am sorry.

I have a question:

In the OP's example, the two photons are traveling away from each other at c. I'm going to replace the photons with two massive objects (A and B) and assume they can travel at c.

When A looks towards B, it might at first be thought that B's light would simply appear extremely redshifted. But, if A is truly traveling at c, and B's light approaches A at c, essentially B's light wave would stand still. A would see darkness if it looked in B's direction, correct?

Now, since massive objects are not thought to be able to travel at c, in reality when A looks towards B, it would pick up B's light as an extremely redshifted signal.

Are these explanations correct?