Regarding Gliese581g

[PlasmaBomb]

The Earth IS traveling near the speed of light if you take it compared to the spaceship. The earth is moving away from you at .99c. This is some of the very basics of relativity. Nether frame of reference is "better" than the other.

Isn't the inertial frame of reference preferred?

How about this, take two spaceships A and B. Both are moving in the same direction with respect to the earth. Spaceship A and the earth are moving away from each other at .99c, spaceship B and spaceship A can also be moving away from each other at .99C. But this does not mean that spaceship B and the earth are moving away from each other at 1.98c. Instead spaceship B and the earth will be moving away from each other at something like .99995c

I am going to need clarification on this too... because either you are wrong or you have said one thing and meant another.

Your example is -

Earth.... Ship A 0.99c -> ...... Ship B 0.99 c->

So ship A would see ship B moving a 0c

The figures you are using describe this situation...

<-0.99c Ship A....Earth.....Ship B 0.99c->

and ship A would indeed see ship B receding at 0.99995c

 

[PlasmaBomb]

Wrong.

Given the understanding shown by your examples, I am afraid that it is you who is wrong...

Relativistic physics is a bitch though, and as you point out doesn't work according to our classical ideas based on everyday experiences... sorry.

Two objects coming at each other, time dialation ignored, at say .75c will approach each other at 1.5c, but they will still be traveling at .75c. It does not matter that it SEEMS like they are traveling faster to each other, because they just plain aren't.

Paul is correct - it would seem to one ship that the other is closing at 0.96c...

 

[Paul98]

Isn't the inertial frame of reference preferred?



I am going to need clarification on this too... because either you are wrong or you have said one thing and meant another.

Your example is -

Earth.... Ship A 0.99c -> ...... Ship B 0.99 c->

So ship A would see ship B moving a 0c

The figures you are using describe this situation...

<-0.99c Ship A....Earth.....Ship B 0.99c->

and ship A would indeed see ship B receding at 0.99995c

I did not say that. Maybe I should have said ShipA and B are moving away from each other at .99c, and not used the word "can". So ship A and earth are moving away from each other at .99c. Ship B and A are moving away from each other at .99c. Thus, it's Earth -> Ship A -> Ship B.

From Earth it's Earth -> ShipA moving at .99c -> ShipB moving at .99995c

From Spaceship A it's Earth .99c <- ShipA -> ShipB .99c

Then from B it's similar to frame from earth.

Hope that clears things up, once again it seems we are just arguing schematics, as it can be quite hard to explain exactly what we mean. You forget to say what something is respect to or what is accelerating or not and it all of a sudden doesn't make sense.

 

[Biftheunderstudy]

Just to muddle this confusing mess up a bit further...there actually is a preferred frame of reference in our universe. We can measure the red/blue shift of the CMB to get an absolute speed measurement. Yes this is just choosing a reference frame, however it is universal in our particle horizon.

Long story short though, you could build a constant acceleration space ship that would get you there in less than 20 years in your (the spaceships) frame. Communication between the spaceship and the Earth would be a bit of a pain in the butt though.

 

[Ninjahedge]

Given the understanding shown by your examples, I am afraid that it is you who is wrong...

Paul is correct - it would seem to one ship that the other is closing at 0.96c...

Physically impossible.

If time is slowing down from your perspective, and they are traveling through the same space you are, they will appear to be going faster than they are. EVERYTHING will appear to be going faster.

If a car is going 50 MPH and you zip by at close to the speed of light so that time is not passing at 1 second for you and 100 for them, you have just witnessed the car traveling at what YOU perceive it to be, 5,000 mph.

The ONLY thing that relativity talks about is the speed of LIGHT ITSELF and our perception of it. Physical matter does not follow the same rules.

THAT bit of relativity says, if you are traveling at .99c and fire a beam ahead of you, it will appear to be traveling at c as if you were just standing still.

It would ALSO appear to be travelling at c from the stationary observer. The only thing that gets REALLY mind numbing is when you fire the beam out the back of your ship and it still appears to be going the same speed. Time dialation + your own speed should say you see the beam traveling at 1.99c x Time dialation, but you still see it at c.

matter =/ light

 

[Ninjahedge]

Side thought.... How would you get everything in sync with both guys looking out the back window? Ignoring red shift that is.

Whether they see each other traveling at 1.5 c (or traveling AWAY from each other at that rate), how would this appear. Whether or not the other object LOOKS to be going whatever speed you think, all you have to do is measure the distance between to know that they are seperating at faster than c.....

But how would light be able to do that when both guys would see it going at c from the back of their ship, and we would see it going at c between their ships? Time dialation would work if you shot the beam out ahead of you, if you shot it behind it should look like it is going even faster (by our own physical laws)....

 

[Ninjahedge]

Just to muddle this confusing mess up a bit further...there actually is a preferred frame of reference in our universe. We can measure the red/blue shift of the CMB to get an absolute speed measurement. Yes this is just choosing a reference frame, however it is universal in our particle horizon.

Long story short though, you could build a constant acceleration space ship that would get you there in less than 20 years in your (the spaceships) frame. Communication between the spaceship and the Earth would be a bit of a pain in the butt though.

Wasn't that in the Kim Stanley Robinson books?

He did a quick calc to see how much actual mass would be needed to fuel a fusion reactor that would produce 1G of acceleration/deceleration to some place like Neptune.... I was kind of surprised at how much would be needed to propel anything of any worth that far that fast.....

(BTW, Red, Blue and Green mars. EXCELLENT books).

 

[Paul98]

Ninjahedge In relativity and at high speeds things don't work the same way we see them work in every day life. It makes this tricky to understand at first. But once you understand the basics you can make the same conclusions that Einstein did.

Speed is relative, it only depends on which object you chose to compare your speed to.

Speed of light is constant in a vacuum in all frames of reference. It does not matter how fast you are going with respect to other objects you will always see light moving away or to you at c.


Take two spaceships approaching each other at the combined speed of .9c. Both spaceships have a light clock that sends a beam of light back and fourth from the bottom to the top of the craft. In the frame of reference of the crafts the light in there own clock only has to move the height of the craft. But if we are to look at the other craft the beam of light has to move farther due to the motion. So we see the beam having to move the same height but also forward so it will hit the mirror on the top. So if one spaceship checks to see how long the beam of light takes on the other craft to go from bottom to top it takes longer, as light is moving at c but has farther to go. Both spaceships see there own beam of light take a short time and the others beam of light to take a longer time.

There are other things that some of the basics lead to. Like length contraction where things are shorter when approaching the speed of light. Relativity of simultaneity where two frames of reference will not agree at the timing of two things. Like you could have two flashes of lightning happen at the same time in one frame and happen at two different times in another frame.

 

[Ninjahedge]

The beam does not "move" when it goes up and down.

If you looked at it with "super sight" you would see the beam traveling back and forth with a curved trail behind it (a sine wave). We just do not see this because we see light traveling instantly in our own frame of reference.

The thing is, all these analogies keep thinking that matter will somehow behave like light once you get close enough to its speed. I do not think that is possible. There is something that makes the rules different for material objects and EM radiation that sets up a barrier at the speed of light.

Here's the question. If these guys are traveling away from each other at .5c. One shoots a beam of light to the other once a second. At the start, the ships are exactly 1 light second away from each other. How long will it take for the beam to get from ship to ship?

It travels at c, regardless of the speed of the other two. You launch it at t=0, that means to get to the original place the second ship was in, it would take a second, but that ship has already moved a half light second away (0.5c).

Roll forward another half second and it is another quarter second away(0.5c x 0.05s = 0.25ls). Continue this progression until the light catches up up the ship. 2 seconds. (do the math).

The second pulse started when the ship was 1.5 away. That will take the light 3 seconds to get to the other ship.

So, the second clock is now showing that the first pulse took 2 seconds to go, and the 2nd took 3.

The first pulse, sent at t=0 was 2 light-seconds in travel. The second pulse, at t=1, took 3 seconds. Between time 1 and 2, the ships seperated 1 light second. So in one second, the ships seperated an additional light second. It took light an extra second to go between them (no time dialation). Therefore they seperated at the speed of light.

 

[Paul98]

The beam does not "move" when it goes up and down.

If you looked at it with "super sight" you would see the beam traveling back and forth with a curved trail behind it (a sine wave). We just do not see this because we see light traveling instantly in our own frame of reference.

So what is the speed of light that we have been talking about?

The thing is, all these analogies keep thinking that matter will somehow behave like light once you get close enough to its speed. I do not think that is possible. There is something that makes the rules different for material objects and EM radiation that sets up a barrier at the speed of light.

at no point did we talk about matter will behave like light when it gets close to the speed of light. We aren't making analogies ether I am giving conditions and saying what would actually be happening.

Here's the question. If these guys are traveling away from each other at .5c. One shoots a beam of light to the other once a second. At the start, the ships are exactly 1 light second away from each other. How long will it take for the beam to get from ship to ship?

It travels at c, regardless of the speed of the other two. You launch it at t=0, that means to get to the original place the second ship was in, it would take a second, but that ship has already moved a half light second away (0.5c).

Roll forward another half second and it is another quarter second away(0.5c x 0.05s = 0.25ls). Continue this progression until the light catches up up the ship. 2 seconds. (do the math).

The second pulse started when the ship was 1.5 away. That will take the light 3 seconds to get to the other ship.

So, the second clock is now showing that the first pulse took 2 seconds to go, and the 2nd took 3.

The first pulse, sent at t=0 was 2 light-seconds in travel. The second pulse, at t=1, took 3 seconds. Between time 1 and 2, the ships seperated 1 light second. So in one second, the ships seperated an additional light second. It took light an extra second to go between them (no time dialation). Therefore they seperated at the speed of light.

t = 0
ship is 1ls away
first beam sent
t = 1
ship is 1.5ls away
first beam is 1ls away
second beam sent
t = 2
ship is 2ls away
first beam hits ship
second beam is 1ls away
t = 3
ship is 2.5ls away
second beam is 2ls away
t = 4
ship is 3ls away
second beam hits ship.

So as you can see the second beam at t = 1 takes 3 seconds, and they distance traveled is 1.5ls. So you are moving away at .5c just as you said at the start.

The reason that the second beam hits only a second after the first one hits is because it was sent a second later. It doesn't matter how fast you are moving away. If you are sending beams 1 second after each other after the first beam hits each one after will hit 1 second apart.

 

[Ninjahedge]

at no point did we talk about matter will behave like light when it gets close to the speed of light. We aren't making analogies ether I am giving conditions and saying what would actually be happening.

Yes you did.

By saying that a physical object cannot be perceived as traveling faster than the speed of light when it really isn't, you were saying matter behaved like light.

You are screwing up my analogy.

Ship 1 and 2 are traveling away from each other at 0.5c
Ship 1 is at -0.5ls
Ship 2 is at 0.5ls
Ship sends a beam (1) to ship 2
At 1 second:
Ship 1 is at -1.0ls
Ship 2 is at 1.0ls
Beam 1 is at 0.5ls (Started at -0.5, traveled +1 second)
Ship 1 sends out beam 2
2 seconds:
Ship 1 is at -1.5ls
Ship 2 is at +1.5ls
Beam 1 is at 1.5ls (-0.5+2) Ship 2 receives beam.
Beam 2 is at 0ls
3 seconds:
S1 = -2ls
S2 = +2ls
B2 = 1ls
4 seconds:
S1 = -2.5ls
S2 = +2.5ls
B2 = +2ls
5 seconds
S2 = 3ls
B2 = 3ls - S2 receives beam.
(My fault for not including the extra second in travel on the original calc)

So, in one second the amount of time it takes light to go from one ship to another has increased from 2 seconds to 4 seconds.

Back calculating, you get, obviously, 2 and 4 ls as the distances at those times (double the starting distances). You would need to be seperating at 1.0c in order to have that happen.

If one ship were standing still, the time taken would have been 2 seconds for the first and 3 seconds for the second.

The key here is simple. Something can be coming toward you or away seemingly faster than light if both are moving:

http://en.wikipedia.org/wiki/Speed_of_light

There are situations in which it may seem that matter, energy, or information travels at speeds greater than c, but they do not. For example, if a laser beam is swept quickly across a distant object, the spot of light can move faster than c, although the initial movement of the spot will be delayed because of the time it takes light to get to the distant object at the speed c. However, the only physical entities that are moving are the laser and its emitted light, which travels at the speed c from the laser to the various positions of the spot. Similarly, a shadow projected onto a distant object can be made to move faster than c, after a delay in time.[35] In neither case does any matter, energy, or information travel faster than light.

This, however, is seriously cool (I heard of this)

Certain quantum effects are transmitted instantaneously and therefore faster than c, as in the EPR paradox. An example involves the quantum states of two particles that can be entangled. Until either of the particles is observed, they exist in a superposition of two quantum states. If the particles are separated and one particle's quantum state is observed, the other particle's quantum state is determined instantaneously (i.e., faster than light could travel from one particle to the other). However, it is impossible to control which quantum state the first particle will take on when it is observed, so information cannot be transmitted in this manner.[36][37]

It implies that there IS some trans-dimensional thing that allows a seperated atomic particles quantum state to change simultaneously over a distance instantaneously. Question is, are they connected, or are they just exact copies/change at the same time (like really good watches)?

The bottom line is, objects CAN appear to be travelling faster than the speed of light, so long as nothing actually IS travelling faster than it. And appear is a bit of a misnomer as well, since light is what we generally use to observe things. The closer we get to c, the harder it would be to compensate not only for the lag, but for the observational time dialation......


Anyway, you can keep saying whatever you want, or do a quick 10 minute Google and see that you are just a bit off in your reasoning.

>shrug<

 

[Paul98]

Yes you did.

By saying that a physical object cannot be perceived as traveling faster than the speed of light when it really isn't, you were saying matter behaved like light.

You are screwing up my analogy.

Ship 1 and 2 are traveling away from each other at 0.5c
Ship 1 is at -0.5ls
Ship 2 is at 0.5ls

if ship 1 is moving a away from a mid point at .5c and ship 2 is moving away in the other directing at .5c. is what you mean to say. Which means that from ether ship they are moving away from the other at .8c.

http://en.wikipedia.org/wiki/Velocity-addition_formula

(.5 + .5)/(1 + (.5*.5)) = .8c

Ship sends a beam (1) to ship 2
At 1 second:
Ship 1 is at -1.0ls
Ship 2 is at 1.0ls
Beam 1 is at 0.5ls (Started at -0.5, traveled +1 second)
Ship 1 sends out beam 2
2 seconds:
Ship 1 is at -1.5ls
Ship 2 is at +1.5ls
Beam 1 is at 1.5ls (-0.5+2) Ship 2 receives beam.
Beam 2 is at 0ls
3 seconds:
S1 = -2ls
S2 = +2ls
B2 = 1ls
4 seconds:
S1 = -2.5ls
S2 = +2.5ls
B2 = +2ls
5 seconds
S2 = 3ls
B2 = 3ls - S2 receives beam.
(My fault for not including the extra second in travel on the original calc)

So, in one second the amount of time it takes light to go from one ship to another has increased from 2 seconds to 4 seconds.

Back calculating, you get, obviously, 2 and 4 ls as the distances at those times (double the starting distances). You would need to be seperating at 1.0c in order to have that happen.

Obviously they are moving away from each other aka "seperating" at 1c when compared to a mid point. That's exactly what you said at the start.

Anyway, you can keep saying whatever you want, or do a quick 10 minute Google and see that you are just a bit off in your reasoning.

>shrug<

Main problem is that you are not understanding some of the basics of relativity. Check out here and it should help.

http://en.wikipedia.org/wiki/Introd..._and_Galilean_relativity:_a_classical_prelude


Or head to www.physicsforums.com and go to the relativity section and write there what you have been writing here. They can quickly show you what I have been talking about or do some searches in that forum.

 

[uclabachelor]

It's great to know these planets exist, but it's also kinda sad. It's sad because I know that I will never know what life exists on this planet, because:

- We need to develop fast as light or faster than light travel. Not happening.
- Even then it will take years to get there.
- So we need epic deep space life support, also not available.

D:

You don't need to do any travelling at all. In a few decades, there will be instruments that are sensitive enough to pick up the light reflecting off the planet to determine the chemical composition of the atmosphere due to advances in technology, sensors, and computing power.

 

[Ninjahedge]

UCLAB.. They might be able to get an idea, but I do not know if they would be able to get the linons share of what that planet had to offer.

Uranus may be made of solid gold once you get down to it but all the light reflections would be able to tell you is what is in the crust.

Come to think of it, aside from our own desire for it, gold is kind of useless foe colonization. It would be GREAT for electronics though (Imagine gold at $5 an ounce and how easy it would be to get contacts that never tarnish???).

I think the biggest problem we will have with coloniaation will not be technical, but social and political.

We can't keep from fighting each other on this rock we call home, how would we get a few thousand up in a ship the size of Randall's Island for 20 years without problems?