Relativity and time question for physics enthusiasts

[Vic]

Originally posted by: Eli
Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

Imagine being in a car moving at speed on the freeway and throwing a ball up into the air (inside the car). Despite being complete disconnected from anything in the car, the ball will still move relative to car. If you throw the ball outside the car, the ball will cease moving relative to the car and will suddenly fly backwards. Make sense?
Now imagine the car is travelling infinitely close to the speed of light. If you throw the ball forward to bounce off the windshield, according to relativity during that period the ball would have to travel faster than the speed of light. That is not possible. As the speed of light is a universal constant, the simple answer is that relative time slows down the closer you get to it.

edit: per Einstein, this is how he came up with the idea, but substitute car for train.

 

[Heisenberg]

Originally posted by: Descartes
Known in what way? That's something of a Platonic view, no? The phenomenon might have been known, but he provided the quantitative footing same as Newton to mechanics. It's been a long while since I read any treatise on Maxwell, so color me a bright shade of moron if I speak falsely.

No, the equation's were known before Maxwell. He basically just fixed Ampere's law, and stuck all of them together in one group IIRC.

 

[hjo3]

Originally posted by: Vic
Someone correct my figures if I'm wrong (I used the equation of Acceleration = (Final Velocity) - (Original Velocity) / Time), but at a constant acceleration of 2G's (which would be quite uncomfortable over time), it would take 177 days 10 hours and 39 minutes to reach 0.99c.

Ehh, are you accounting for the ship's mass increasing as it approaches C?
Or is the engine just capable of far more than (original ship mass x 2) thrust, and the pilot voluntarily throttles it back at the beginning?

 

[RaynorWolfcastle]

Here's a thought experiment that's fun the first time you see it.

What happens if 2 astronauts are having an interstellar game of chicken? Each astronaut is in his spaceship flying directly towards the other in a space ship that's going at 0.7c, how fast do they perceive the other astronaut's speed to be?

 

[hjo3]

Originally posted by: RaynorWolfcastle
Here's a thought experiment that's fun the first time you see it.

What happens if 2 astronauts are having an interstellar game of chicken? Each astronaut is in his spaceship flying directly towards the other in a space ship that's going at 0.7c, how fast do they perceive the other astronaut's speed to be?

Uh... dunno... but each one would look really blue to the other!
EDIT: Actually, if something was coming at you that fast, would the blue shift be enough to push its reflected light frequency above the visible spectrum so it'd be essentially invisible to you?

 

[Vic]

Originally posted by: hjo3

Originally posted by: Vic
Someone correct my figures if I'm wrong (I used the equation of Acceleration = (Final Velocity) - (Original Velocity) / Time), but at a constant acceleration of 2G's (which would be quite uncomfortable over time), it would take 177 days 10 hours and 39 minutes to reach 0.99c.

Ehh, are you accounting for the ship's mass increasing as it approaches C?
Or is the engine just capable of far more than (original ship mass x 2) thrust, and the pilot voluntarily throttles it back at the beginning?

Heh, I'm no physicist, though I understand that mass increases closer to C. I seem to recall, however, that the current theories of rocket propulsion through a vacuum require descreasing mass because you are ejecting mass.

 

[Eli]

Is going faster than the speed of light actually technically impossible, or do we just not know any means?

Speed seems like such an arbitrary thing, it seems strange that there would be any sort of limit... given enough energy? or something.

What's so special about a photon?

lol

 

[silverpig]

Originally posted by: Descartes

Originally posted by: silverpig

Originally posted by: Descartes

Originally posted by: Heisenberg

Originally posted by: Eli
Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

Sort of. All of this weirdness follows from the speed of light being the ultimate speed limit. That's really what Einstein just whipped out one day.

This is always said, but wouldn't some credit to Faraday, Maxwell, and Roemer have to be given here? Understandably, Einstein included the postulate that "no information can travel faster than 'c'", but that wasn't much more than a derivation of what was already known. Right? Einstein pushed the issue into new light (pun intended), but I wouldn't say he just whipped it out. Without Lorentz, Newton, Faraday, Maxwell, Roemer, Galileo, etc. to supplicate he wouldn't have had relativity either special or general.

imo.

Meh I don't know about Maxwell. Of the 4 "Maxwell's equations" he only modified one of them (added time dependence of a magnetic field or something IIRC). The other 3 were known

Known in what way? That's something of a Platonic view, no? The phenomenon might have been known, but he provided the quantitative footing same as Newton to mechanics. It's been a long while since I read any treatise on Maxwell, so color me a bright shade of moron if I speak falsely.

Known as in the exact equations were written down by other people at other times in other books. He just put them all together and added one term (+ dB/dt IIRC) to one of them.

 

[Descartes]

Originally posted by: silverpig

Originally posted by: Descartes

Originally posted by: silverpig

Originally posted by: Descartes

Originally posted by: Heisenberg

Originally posted by: Eli
Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

Sort of. All of this weirdness follows from the speed of light being the ultimate speed limit. That's really what Einstein just whipped out one day.

This is always said, but wouldn't some credit to Faraday, Maxwell, and Roemer have to be given here? Understandably, Einstein included the postulate that "no information can travel faster than 'c'", but that wasn't much more than a derivation of what was already known. Right? Einstein pushed the issue into new light (pun intended), but I wouldn't say he just whipped it out. Without Lorentz, Newton, Faraday, Maxwell, Roemer, Galileo, etc. to supplicate he wouldn't have had relativity either special or general.

imo.

Meh I don't know about Maxwell. Of the 4 "Maxwell's equations" he only modified one of them (added time dependence of a magnetic field or something IIRC). The other 3 were known

Known in what way? That's something of a Platonic view, no? The phenomenon might have been known, but he provided the quantitative footing same as Newton to mechanics. It's been a long while since I read any treatise on Maxwell, so color me a bright shade of moron if I speak falsely.

Known as in the exact equations were written down by other people at other times in other books. He just put them all together and added one term (+ dB/dt IIRC) to one of them.

Yeah, I just read that here. Most descriptions of Maxwell that I've read rather imply that he derived them entirely, and seem to give little description of them pre-Maxwell.

Thanks to you and Heisenburg for the clarification.

 

[Heisenberg]

Originally posted by: Eli
Is going faster than the speed of light actually technically impossible, or do we just not know any means?

Speed seems like such an arbitrary thing, it seems strange that there would be any sort of limit... given enough energy? or something.

What's so special about a photon?

lol

Nope, it's not allowed. It would require infinite energy to accelerate a massive particle to c. A photon has no mass so it can travel at c.

 

[Descartes]

Originally posted by: Eli
Is going faster than the speed of light actually technically impossible, or do we just not know any means?

Speed seems like such an arbitrary thing, it seems strange that there would be any sort of limit... given enough energy? or something.

What's so special about a photon?

lol

Heisenburg already answered your questions, but you can also Google around for "tachyon" and "causality problem." These will turn up most of the discussions on FTL travel.

 

[silverpig]

Originally posted by: Eli
Is going faster than the speed of light actually technically impossible, or do we just not know any means?

Speed seems like such an arbitrary thing, it seems strange that there would be any sort of limit... given enough energy? or something.

What's so special about a photon?

lol

There's nothing saying that you can't go faster than light really. The physics of things travelling faster than light are similar to those travelling slower than light, but they have a bunch of negative signs thrown in there, and some imaginary numbers as well. The equations all work out AFAIK.

The thing is once you go faster than light, you start seeing negative signs in the time terms of equations, so you actually start travelling backwards in time in a way. This violates some other principles we have, but these principles exist based on the assumption that nothing can go faster than light.

It is physically impossible for us to go faster than light right now as it would take an infinite amount of energy to accelerate something to light speed, however you can apparently go faster than light as the example of travelling 8 ly in 0.5 yrs says in this thread. You just have to be a bit creative with which time and which distances you're using.

 

[hjo3]

Originally posted by: Vic

Originally posted by: hjo3

Originally posted by: Vic
Someone correct my figures if I'm wrong (I used the equation of Acceleration = (Final Velocity) - (Original Velocity) / Time), but at a constant acceleration of 2G's (which would be quite uncomfortable over time), it would take 177 days 10 hours and 39 minutes to reach 0.99c.

Ehh, are you accounting for the ship's mass increasing as it approaches C?
Or is the engine just capable of far more than (original ship mass x 2) thrust, and the pilot voluntarily throttles it back at the beginning?

Heh, I'm no physicist, though I understand that mass increases closer to C. I seem to recall, however, that the current theories of rocket propulsion through a vacuum require descreasing mass because you are ejecting mass.

Sure, but I'd assume you'd have a really efficient engine if it's capable of 2 Gs of acceleration for more than a month. So maybe you're getting 20 tons of thrust (in a 10 ton spaceship) by throwing out an ounce of hydrogen per second at a very, very high speed. But at a 14.1:1 time dialation, your ship masses 141 tons... and you're only losing an ounce per second. Not quite equal.

 

[Vic]

Problem with FTL travel: we don't have the ability to create/control the energy required to get there.

Benefit if we ever solve that problem: it will be instantaneous.

 

[Heisenberg]

Originally posted by: silverpig
There's nothing saying that you can't go faster than light really. The physics of things travelling faster than light are similar to those travelling slower than light, but they have a bunch of negative signs thrown in there, and some imaginary numbers as well. The equations all work out AFAIK.

The thing is once you go faster than light, you start seeing negative signs in the time terms of equations, so you actually start travelling backwards in time in a way. This violates some other principles we have, but these principles exist based on the assumption that nothing can go faster than light.

It is physically impossible for us to go faster than light right now as it would take an infinite amount of energy to accelerate something to light speed, however you can apparently go faster than light as the example of travelling 8 ly in 0.5 yrs says in this thread. You just have to be a bit creative with which time and which distances you're using.

Yeah, I think it'd be more accurate to say that you can't travel FTL in a local frame. Of course then you have to define exactly what a local frame is..

There are theories about using wormholes to travel FTL. Because a wormhole would link two distant points in space, you could travel FTL from the view of somebody outside your reference frame (since you went a great distance in a short time), but never exceed c locally since the distance you saw was very small. Of course wormholes present their own problems, one of which is requiring particles with a negative energy and mass, which is not prohibited by quantum mechanics, but nobody's really sure if it's allowed either last I heard.

 

[hjo3]

Originally posted by: Vic
Problem with FTL travel: we don't have the ability to create/control the energy required to get there.

Benefit if we ever solve that problem: it will be instantaneous.

But at C, your mass would be infinite, right? So one might imagine you and and your vessel would just sort of collapse inward like a tiny blackhole or something.

 

[Vic]

Originally posted by: hjo3
Sure, but I'd assume you'd have a really efficient engine if it's capable of 2 Gs of acceleration for more than a month. So maybe you're getting 20 tons of thrust (in a 10 ton spaceship) by throwing out an ounce of hydrogen per second at a very, very high speed. But at a 14.1:1 time dialation, your ship masses 141 tons... and you're only losing an ounce per second. Not quite equal.

I knew I shouldn't have brought up the acceleration problem. See, the real problem is that we can't get there from here.

 

[DWW]

Originally posted by: Vic
Problem with FTL travel: we don't have the ability to create/control the energy required to get there.

Benefit if we ever solve that problem: it will be instantaneous.

You know, the individual (if its one person) that develops a stable FTL system will be the richest person ever. Why? Imagine all of the resources available to him/her heh. "billions and billions" of planets and galaxies for their taking

But that asks the question, who "owns" space. Is it the collective sum of earth that should be entitled to it, or are you entitled to nothing? If someone managed to create FTL system are they expected to share?

 

[silverpig]

Originally posted by: Vic

Originally posted by: hjo3
Sure, but I'd assume you'd have a really efficient engine if it's capable of 2 Gs of acceleration for more than a month. So maybe you're getting 20 tons of thrust (in a 10 ton spaceship) by throwing out an ounce of hydrogen per second at a very, very high speed. But at a 14.1:1 time dialation, your ship masses 141 tons... and you're only losing an ounce per second. Not quite equal.

I knew I shouldn't have brought up the acceleration problem. See, the real problem is that we can't get there from here.

yet...

 

[z0mb13]

NERD ALERT! NERD ALERT!

man physicists are actually worse than nerds

 

[Descartes]

Originally posted by: DWW

Originally posted by: Vic
Problem with FTL travel: we don't have the ability to create/control the energy required to get there.

Benefit if we ever solve that problem: it will be instantaneous.

You know, the individual (if its one person) that develops a stable FTL system will be the richest person ever. Why? Imagine all of the resources available to him/her heh. "billions and billions" of planets and galaxies for their taking

But that asks the question, who "owns" space. Is it the collective sum of earth that should be entitled to it, or are you entitled to nothing? If someone managed to create FTL system are they expected to share?

The question of who owns space is a sociopolitical (not to mention anthropocentric--who's to say humans are entitled?) question, imo, and so should not (although many people mix the magisteriums of science with politics, etc. often) elicit or require scientific justification. I'd hate to think of people holding power of such expansive spatial boundaries. *shudder*

 

[RaynorWolfcastle]

Originally posted by: z0mb13
NERD ALERT! NERD ALERT!

man physicists are actually worse than nerds

...says the man too inept to book his own honeymoon

 

[z0mb13]

Originally posted by: RaynorWolfcastle

Originally posted by: z0mb13
NERD ALERT! NERD ALERT!

man physicists are actually worse than nerds

...says the man too inept to book his own honeymoon

that wasnt me dude..

 

[RaynorWolfcastle]

Originally posted by: z0mb13

Originally posted by: RaynorWolfcastle

Originally posted by: z0mb13
NERD ALERT! NERD ALERT!
man physicists are actually worse than nerds

...says the man too inept to book his own honeymoon

that wasnt me dude..

Hmmm... I checked, and the guy I was thinking of has the handle "zombie", that explains the confusion.