So what happens if you try to accelerate to, or past, light speed?

So what happens if you try to accelerate to, or past, light speed?

Me? I make oopsie in my shorts.

In other words? I got no clue, sorry.

Okay, I think thrusters could provide constant acceleration at newtonian speeds, but they wouldn't at speeds approaching c. They would provide constant force, which would cause less and less acceleration as you approach c. Once the maximum speed is attained, in a frictionless environment you could maintain that speed without thrust (that's true at any speed, be it slow or close to c), but i think in reality the vacuum of space does provide a teensy amount of friction (um, space dust? gravity from nearby things?). So my best guess is that you would slow down very very slowly with no thrust.

If you want to make an excuse for going faster than light, wikipedia offers the following: http://en.wikipedia.org/wiki/Faster-than-light#Justifications

(c=the speed of light, for those of you playing along at home)

It is just as if your mass increases, the faster you go.

So your thrusters (providing constant force) which were providing acceleration of 'A[SUB]1[/SUB]' m/s/s at slow speeds are now only providing 'A[SUB]2[/SUB]' m/s/s of acceleration of at speed 'v' ... where:

A[SUB]2[/SUB] = A[SUB]1[/SUB] * sqrt(1-v[SUP]2[/SUP]/c[SUP]2[/SUP])

So as 'v' approaches 'c', your acceleration approaches 0.

The model of pretending the mass has increased has fallen out of favour in recent years, but it is an easy way to visualise it.

Mac

I also think that since time slows down as you approach the speed of light, you won't notice your accelleration decreasing; Your accelleration doesn't decrease relative to you, but only to other people (who are not going so fast).

You asymptotically approach the speed of light. (Antelope Freeway one half mile. Antelope Freeway one quarter mile. Antelope Freeway one eighth mile. Antelope Freeway one sixteenth mile. etc.)

I've just always heard the condensed, for-the-layman explanation: as you approach lightspeed, your mass approaches infinite, and so (as stated above already) each acceleration requires more energy to accelerate your increased mass ... Since it would take INFINITE energy to push you over lightspeed, and the Universe doesn't have that much juice ... lightspeed is impossible.

Another explanation I've heard is this: Space/Time is a thing where, you never "move" thru the combined Space/Time faster than the speed of light: If you just sit there with no acceleration in SPACE, all movement is through TIME (our normal time passes)

Any motion you make through SPACE, slows your acceleration through TIME, so that as you approach lightspeed moving in SPACE, you're slowing your motion through TIME: you can never hit lightspeed because (once again) the increments slow you through TIME ... and TIME stops before you can ever be moving at lightspeed.

Can that be right? Why would Time stop for the INSIDE, accelerating relativistic observer?

I grasp that the NON-accelerating observer left behind would seem to experience increased time-passage (the familiar "I traveled in my starship for a year, and 1000 years had passed back on Earth") ... but how is it that the person INSIDE the starship experiences "Time stopping" FOR THEM at lightspeed?

Can someone explain/correct my mis-understanding there?

small axe said:

Can someone explain/correct my mis-understanding there?

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For a passenger, the interior of the ship would not change. The one G acceleration would still plant her feet on the floor. By the ship's gauges, the fuel use would remain constant. Outside would be a different story, though. Stars in the forward screen would turn blue, then ultraviolet, while those in the rear screens would turn red, then infrared. The galaxy would seem distorted, as though squashed in the direction of travel. Stars would get so close together that you could travel between them in very little time. Go fast enough, and you could cross the galaxy in just a few minutes, ship time. This is due to time dilation, of course. From the POV of someone still at home, a hundred thousand years will have passed.

Travelling at light speed, as photons do, no time passes at all. A photon crosses the universe in an instant by it's own reckoning.

Julie Worth said:

For a passenger, the interior of the ship would not change. The one G acceleration would still plant her feet on the floor. By the ship's gauges, the fuel use would remain constant. Outside would be a different story, though. Stars in the forward screen would turn blue, then ultraviolet, while those in the rear screens would turn red, then infrared. The galaxy would seem distorted, as though squashed in the direction of travel. Stars would get so close together that you could travel between them in very little time. Go fast enough, and you could cross the galaxy in just a few minutes, ship time. This is due to time dilation, of course. From the POV of someone still at home, a hundred thousand years will have passed.

Travelling at light speed, as photons do, no time passes at all. A photon crosses the universe in an instant by it's own reckoning.

Click to expand...

I guess that's what my mind was rebeling against (and perhaps is still unclear to me, from your comments): Would the crew inside the ship experience Time continuing to pass, despite an outside observer thinking "Time has stopped for them, like for the photons" ???

If so ... would the CREW inside live 70 years then die of normal "time passing/old age" (according to the crew) ... but never die according to the outsider who thinks NO TIME can be passing for the crew?

Would it be a sensation of "living forever, but it felt like only 70 years?"
or
"we lived forever in a moment" (In which case, since one action must follow another action, in two different moments ... how's that POSSIBLE?)

Never mind that if the CREW is living FOREVER (even relativistic "forever") ... what happens when the Universe ages and dies around them at the end of Time ... if the crew has escaped Time?

I'm ranting. But any insights/advice would be helpful!

This thread makes my head hurt ... If I'm going at lightspeed, I'm obviously going way too fast, so I'd put myself on autopilot and hope that Otto won't drive me into a meteor, asteroid, other space ship, or small planet.

Our current understanding of physics does not allow for such speeds due to the amount of energy required. Even at light speed, travel to the nearest star would require a massive expenditure or time and energy. Many theories have been proposed for solving the problem. Probably one of the most promising means of traversing vast expanses is the theoretical worm hole. As for your question conserning deseleration; Short distance travel, i.e. star to star, once you reach your 99.9c, your speed should remain constant without the need for additional thrust. But space debree could wreak havoc on your trip.

dpaterso said:

You'll continue to accelerate, but in ever-decreasing fractional increments beyond 99.9%. You'll never reach c

Unless you have an onboard fuel synthesizer or the capability of collecting external elements to use as fuel, deceleration could be problematic.

-Derek

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You just keep an eye on the fuel gauge, and hope it's accurate. You have to start slowing down when you've used up half your fuel.

small axe said:

I've just always heard the condensed, for-the-layman explanation: as you approach lightspeed, your mass approaches infinite, and so (as stated above already) each acceleration requires more energy to accelerate your increased mass ... Since it would take INFINITE energy to push you over lightspeed,

Click to expand...

Not even OVER lightspeed, it would take infinite energy to get up TO lightspeed.

small axe said:

and the Universe doesn't have that much juice ... lightspeed is impossible.

Another explanation I've heard is this: Space/Time is a thing where, you never "move" thru the combined Space/Time faster than the speed of light: If you just sit there with no acceleration in SPACE, all movement is through TIME (our normal time passes)

Any motion you make through SPACE, slows your acceleration through TIME, so that as you approach lightspeed moving in SPACE, you're slowing your motion through TIME: you can never hit lightspeed because (once again) the increments slow you through TIME ... and TIME stops before you can ever be moving at lightspeed.

Click to expand...

That's a weird way to look at it that I've never read before, and looks correct to me except for that last statement. Time only stops AT lightspeed, and mass cannot get TO lightspeed, it can only approach it, so time will slow down (relative to a non-accelerating observer), but not stop.

Time on the ship, as seen by a fixed observer, slows down as the ship approaches lightspeed.

small axe said:

Can that be right? Why would Time stop for the INSIDE, accelerating relativistic observer?

I grasp that the NON-accelerating observer left behind would seem to experience increased time-passage (the familiar "I traveled in my starship for a year, and 1000 years had passed back on Earth") ... but how is it that the person INSIDE the starship experiences "Time stopping" FOR THEM at lightspeed?

Can someone explain/correct my mis-understanding there?

Click to expand...

The "non-accelerating" observer on Earth sees the speeding ship's clock slowing down (even discounting the fact that the ship may be going away, causing a doppler frequency shift, which is itself NOT a relativistic effect), and the traveler sees a clock on Earth speeding up.

Each observer sees his own clock as always going at 'the right speed'. It's not that "time slows down" on the ship - the "time" on the ship is always "correct" in that frame of reference, just as the time on Earth is always 'correct' for Earth.

You couldn't hit the speed of light due to the mass of your ship increasing as you got closer. Newtonian physics are pretty accurate up to about 10% the speed of light, after which all bets are off.

A person on the ship simply experiences time differently. To them, in their frame of reference, time is passing as normal, however to an outside observer time is passing extremely slowly for the people on a ship. In effect, if a ship could get up to like 99% C, it could easily travel hundreds of lightyears inside of the the lifetime of the crew. In effect a spaceship like this is in a way a time machine. It allows for people to travel to the future, simply because they experience time at a different rate than those at a different frame of reference.

Dommo said:

You couldn't hit the speed of light due to the mass of your ship increasing as you got closer. Newtonian physics are pretty accurate up to about 10% the speed of light, after which all bets are off.

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Well, it depends on how accurate you mean by 'pretty accurate.' The planet Mercury doesn't orbit the Sun anywhere near 10 percent of lightspeed, but 100 years ago they were wondering why their predictions of its orbit were ever so slightly off.

small axe said:

I guess that's what my mind was rebeling against (and perhaps is still unclear to me, from your comments): Would the crew inside the ship experience Time continuing to pass, despite an outside observer thinking "Time has stopped for them, like for the photons" ???

Click to expand...

Time passes normally for the people in the ship. Any experiment they can do inside the ship shows no difference at all. It's just the outside world that seems distorted.

At light speed, the outside world reaches a maximum distortion. It seems paper thin, and you cross the universe in an instant. If you could go faster than light speed, you'd go back in time.

dpaterso said:

Your scientific source for this bold statement?

-Derek

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Actually, as ship time becomes imaginary if you exceed the speed of light, it's hard to say where you'd end up.

If ship time is T and time on the home planet is t, then (from special relativity) T=t(1-v[SUP]2[/SUP]/c[SUP]2[/SUP])[SUP].5[/SUP]
So when v>c, you're taking the square root of a negative number.

The problem with going faster than the speed of light is getting over the hump at exactly the speed of light, which requires infinite energy for anything with mass. But what if something is created going faster than c so it doesn't have to cross the hump? Tachyons are theoretical particles that aways travel faster than c, but there's never been any evidence for them.

Its logical, just not correct. Its just that the flow of time seems to be related to entropy, and theres no reason speed could affect entropy.

Although, who am I to say?

By accurate, I mean accurate to the point where it's still useful. Within say a margin of error of like 10-20%.

I definitely wouldn't want to plot a starship course using Newtonian approximation at interstellar distances, but for interplanetary stuff, it's probably good enough.

Julie Worth said:

Time passes normally for the people in the ship. Any experiment they can do inside the ship shows no difference at all. It's just the outside world that seems distorted.

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So (???) the crew inside the lightspeed ship thinks "Time feels (at lightspeed inside the ship) like it is advancing at the normal rate for us" ...

Cause-and-effect remains the same: they flip a coin, one second later it hits the floor, same as on Earth.

But to an outside observer on Earth (if they could see what occurs inside the starship, which I know they cannot) ... to them, Time seems to have stopped when the starship hit lightspeed? So ... do they see the crew as FROZEN in Time, where the coin is frozen in mid-air, never falling? Where there can be NO cause-and-effect because there is never the second moment in which anything can result?

The crew is alive and thinking and watching the coin fall, in the exact same moment that the earth observer sees them as "frozen in Time" unable to process the next thought?

Is it logical to speak of "the same moment of Time" ... even if for one observer it lasts a moment, and for another it lasts an eternity?

Is it "the same moment" but only with different relativistic DURATION?

It "feels" like the same moment and duration to both observers, right?

Is there NOTHING in the Universe we can call "simultaneous" regardless of acceleration of the observer?

Is even the FIRST MOMENT OF TIME, in the Universe, not the first moment of Time EVERYWHERE (where ever Everywhere was, however compact or inflated "there" was?)

???

small axe said:

So (???) the crew inside the lightspeed ship thinks "Time feels (at lightspeed inside the ship) like it is advancing at the normal rate for us" ...

Click to expand...

Let's take out the singularity (I mean the mathematical one, but perhaps physical, too) that "a mass moving at lightspeed" would cause, and let's say it's moving arbitrarily close to lightspeed, so time flows both on Earth and on the ship, just at greatly different rates. This is an old calculus trick, using infinitesimals instead of zero, so the reciprocal isn't quite infinite.

Even if you had infinite energy, you couldn't get these people in the ship up TO the speed of light in a finite time, because it would take infinite acceleration to do that in a finite amount of time, and you're limited to acceleration of two or three gee's, else the people in the ship get squished flat and die. Not how I want to travel. So let them accellerate for a few years at a little over a gee, and they'll be going at maybe 90 percent or 99 percent of lightspeed.

From Google:

the speed of light = 186 282.397 miles per second

From the (alleged) bumper sticker:

186,202.397 MPH: Not just a good idea, it's the law!

I'm sticking to this point, because your example of a mass (the ship and people in it) going AT THE SPEED OF LIGHT, well, how can I say this, it does not make sense. It's like dividing by zero. There's the high school algebra trick that ends up with 1 = 2, and it all uses "legal" operations, except that early on it sets A=B and then divides by (A-B), hiding (to the uncritical eye) the division by zero.

small axe said:

Cause-and-effect remains the same: they flip a coin, one second later it hits the floor, same as on Earth.

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Yes.

small axe said:

But to an outside observer on Earth (if they could see what occurs inside the starship, which I know they cannot) ... to them, Time seems to have stopped when the starship hit lightspeed? So ... do they see the crew as FROZEN in Time, where the coin is frozen in mid-air, never falling? Where there can be NO cause-and-effect because there is never the second moment in which anything can result?

The crew is alive and thinking and watching the coin fall, in the exact same moment that the earth observer sees them as "frozen in Time" unable to process the next thought?

Click to expand...

In my modified scenario, someone on Earth may live a whole lifetime as the coin on the ship flips over once. There's still cause and effect. Time goes forward in both places.

small axe said:

Is it logical to speak of "the same moment of Time" ... even if for one observer it lasts a moment, and for another it lasts an eternity?

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These other questions depend on the ship going AT THE SPEED OF LIGHT which it won't do.

There ARE interesting questions about "a moment in time" on the ship vs. that on the Earth, mainly because they would be a significant distance from each other, and somoene in one place could not possibly know about something happening in the other "at the same instant" as it happens, due to the delay in the time it takes light to travel from one to the other. But this has nothing to do with time dilation due to acceleration. Here' a "light cone" diagram that demonstrates what I'm saying (it's a short article that mentions a lot of high-fallutin' stuff I'm not familiar with, but at least it's what I'm thinking of):
http://en.wikipedia.org/wiki/Light_cone

small axe said:

Is it "the same moment" but only with different relativistic DURATION?

It "feels" like the same moment and duration to both observers, right?

Is there NOTHING in the Universe we can call "simultaneous" regardless of acceleration of the observer?

Is even the FIRST MOMENT OF TIME, in the Universe, not the first moment of Time EVERYWHERE (where ever Everywhere was, however compact or inflated "there" was?)

???

Click to expand...

The Big Bang is yet another deal, and the speculation I've read of was that time and a lot of other things were bit nebulous back then. But since then time (and most of the laws of physics) has settled down pretty well, and we can measure it real good now. For an example, check out how a GPS receiver tells your position by receiving the signals from GPS satellites.

dpaterso said:

Your scientific source for this bold statement?

-Derek

Click to expand...

I’d forgotten about this one:

There was a young lady named Bright,
Whose speed was far faster than light;
She set out one day
In a relative way,
And returned on the previous night.

OMG. I'm absolutely fascinated by this thread, even though I have no idea what's going on.

'Little Johnny, just for fun
Played with daddy's photon gun
He pulled the trigger with such elation ...

Now he's cosmic
Radiation'

-- Asimov (I think)