/sci/ - Science & Math

too obvious trolling..

>speed
>scalar
>has direction
lolno

The time travels slower for both the ship and the crew.

However, speed is relative, its not that fact that the space ship is moving fast that slows down time, its the change of reference frame. Which I never really understood the details of.

In order to travel backwards in time, youd have to go faster than the speed of light. Which is impossible. Also saying going faster than the speed of light causes you to go back in time isnt quite true. Its an extrapolation of time dilation which is really just a false interpretation.

>>2371054
Here's a genuine question for this shit thread:

Is time a vector or scalar ?

>>2371067
>to travel backwards in time, youd have to go faster than the speed of light
No. Just go in the other direction.

Is speed of light the speed limit for things with mass only? can massless things travel faster?

>>2371084
Do you know what either of those words mean?

>>2371120
Yes I do.
Are you going to answer my question because I cannot answer it?

>>2371104

No, massless "objects" travel at the speed of light.

>>2371136
Even if they're not light?

>>2371130
Ok. In that case, neither of those options are correct. Most often, time is the parameter of your parametrization.

Why doesn't sound travel at the speed of light?

>>2371149
Yes.

>>2371169
"Sound" is not a particle.

>>2371170
That said, I don't know any other massless particles. Neutrinos are close, but they do have mass.

>>2371175
But it's massless, right?

>>2371178
You can't define the properties of a thing that has no coherent existence.

But if you want to talk about acoustic quanta, look up phonons.

>>2371178
"Mass" is something which particles have. "Massless" isn't exactly meaningful unless you're talking about a particle.

>>2371180
GR treats time as one-dimensional.

>>2371166
>time is the parameter of your parametrization.
But what about when we treat time as a dimension, as in relativistic problems? It's got to be either a vector or scalar quantity in our equations right?

>>2371188
My mind is full of fuck. How can particles be massless? Heck, how is "particle" defined?

>>2371180
When you parametrize a curve, your parameter is a real variable. That's what you treat it as in equations.

I'm guessing you've learned about vectors and scalars from physics textbooks, in which case you would probably label time as a scalar quantity.

>>2371197
Photons are massless particles.

>>2371222
That doesn't answer either of my questions.

>>2371228
Why would you think a particles couldn't be massless?

>In particle physics, an elementary particle or fundamental particle is a particle believed not to have substructure
wikipedia

So, basically, if you were in a fighter jet intercepting above the speed of sound, time technically moves slightly slower for you, correct? Or is it basically negligible if not really close to lightspeed?

>>2371104
All massless things must travel at exactly c. All massive things must travel at less than c. If there were such a thing as an object with imaginary mass, it would have to always travel faster than c, but there's nothing to suggest that imaginary mass actually exists.

>>2371253
you pretend to have the imagination to think of anything you like in physics. Surely you are prodigy, no?

>>2371285
Find the time dilation formula and plug in your numbers. You know, like a real scientist.

>>2371291
>All massless things must travel at exactly c
Why is this?

>>2371312
If mass is zero, the energy equation reduces to E = pc. p is momentum, c is... the speed of light in vacuum.

>>2371197
Everything that can be detected -- everything that carries energy -- anything that interacts with other things -- is a particle. A particle with mass is a special kind of particle that can travel slower than c and contain energy even without motion. Hence it has a rest energy, or rest mass.

>>2371309
>4chan
>scientists

>>2371285
Even going at walking speed slows time down but it's so little that it doesn't affect anything. As you can see from this graph, you have to be close to light speed for time to slow down enough that you might use it for something useful.

>>2371338
That said, the time dilation corrections due to relative velocity are need to make GPS satellites work properly.

>>2371312
Because what he said isn't true.

Speed of light is reduced depending on the atmosphere it's travelling through. Only in a vacuum is it max C V:, i learnt that when i was 15 as part of GCSE.

No one here knows what they're saying >_<

>>2371316
>>2371321
Thanks

>>2371312
heuristically you can think of it like this: if a force acts on a particle it accelerates following F = ma (yes, I know but I cant remember if you divide or multiply by gamma) so if m = 0 an infinitesimal force will accelerate it to light speed instantaneously. when a photon is created it must experience a force otherwise it would overlap with the particle creating it.

>>2371353
I know what you're saying. I thought we were all assuming vacuum though.

It's not actually right to say that light "goes slower" in glass, for instance. It just gets absorbed and re-emited a short time later, over and over, leading to a lower "average" velocity.

>>2371357
stfu, F=ma doesn't fit into laws of physics after shit reaches 1/10th speed of light or more. Since particles gain mass for some reason or another x;. It is totally irrelevant.

>>2371353
>Speed of light is reduced depending on the atmosphere it's traveling through
no, the speed of light is always c, in an atmosphere the photons are absorbed and re emitted by the molecules in the air, this causes a delay and so the measured speed decreases, but between the molecules the photon is still traveling at c.

>>2371312
E^2 = (pc)^2 + (mc^2)^2
So if m=0
E = pc
where p is momentum. Momentum can be defined as gamma * m * v, where gamma goes to infinity as v goes to c. Since m=0, the only way for momentum to be non-zero, is if gamma is infinite, meaning v=c.

To actually calculate the momentum for a massless particle, we have to use p = h/lambda, the planck constant divided by the debroglie wavelength

>>2371357
This is way to convince people, but only to shut people up. I wouldn't teach this to an undergrad.

>>2371353
You are retarded. I didn't say "the speed of light", I said "c", which is the speed light (and all other massless particles) travel in vacuums.

>>2371372
for fuck sakes, F=ma still works, you just have to insert gamma, so define <span class="math"> m = \gamma m_0 [/spoiler] with <span class="math"> m_0 [/spoiler] the rest mass, or <span class="math"> a = \frac{d \gamma v}{dt} [/spoiler]. anyone could have relised that (especially after reading what >>2371357 said after it)

>>2371406
Perhaps in special relativity.

>>2371406
Nope

>>2371451
even if you are Josef, just saying nope without explaining why is not an argument.

>>2371451
I should add that I stopped reading at m = gamma m_0

Y'all bakers toasting in a roll bread.

>>2371463
May I refer you to wikipedia, where you may gain knowledge of popular general relativity.

>>2371467
That's a perfectly valid way of doing it. Just because it's not usually used at advanced levels doesn't mean that it doesn't work. It works very well.

>>2371463 even if you are Josef
Am I a deity or what? I can be as wrong as anyone else on this board, that's what science is about, not giving crap about names, facts stand for themselves
(I had my weekly relativity explanation yesterday already, wait until I reset on monday for proper answers on such topics)

>>2371487
Only in special relativity.

><span class="math">m = \gamma m_0[/spoiler]
I used to pretentiously rage against this too on /sci/, since Einstein didn't like it. But I changed my ways after seeing that the UCLA professor who teaches "physics for future presidents" teaches it that way. If it's good enough for him, it's good enough for me.

>>2371477
why would we want to use GR to explain OPs problem?

>>2371496
I just wanted to make sure you don't think that you can use appeal to authority because you usually are rite.

>>2371502
Which is what we're talking about.

>>2371529
Point taken.
m = gamma m_0 basically beats the crap out of everything that makes up special relativity. Time's not a coordinate, no Lorentz transformations etc. Might work in some special cases, but I don't see any educational point in this, since it adds nothing to what the theory is good for. (It's merely enough to provide a "poof there you are" equation if you really want to give the kids something to chew on. Just like inventing Santa.)

>>2371518
No, we're talking about generalising forces from newtonian mechanics to relativity theory. Hence it was due to point out that the proposed solution only works in special relativity.

>>2371041
Let me guess: You also believe that if you drive your car south you'll get better gas mileage than if you drive north, because south is downhill, right?

>>2371552
Besides, as others have pointed out, <span class="math">F=\frac{dp}{dt}[/spoiler] is superior to that... other equation which is being proposed.

>>2371549
so if I remove the [so define m=gamme*m0 with m0 the rest mass, or] part from my post, there isn't a problem anymore? fine, here:

>>2371372
for fuck sakes, F=ma still works, you just have to insert gamma, so define <span class="math"> a= \frac{d \gamma v}{dt} [/spoiler]. anyone could have relised that (especially after reading what >>2371357 said after it)

hope that better. btw, i think this thread has gone a little of topic

>>2371610
It's been months since I've been trolled on sci, and you won't be the one claiming the prize today either.