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# Who's familiar with the conversion? - "In 15 years' ship-time they could reach Andromeda

Tue 10 Nov, 2015 11:26 am
In fifteen years' ship-time the astronauts could reach Andromeda, 2.4 million light-years away?
The speed of the ship is the speed of light, a simple calculation is that in 15 years, the ship will cover a distance of 15 light-years, not 2.4 million light-year distance.
How to properly calculate it?

Context:

Suppose we were able to build a spaceship that could accel-
erate at a constant one g, that is, at the acceleration of gravity on
Earth, which would also nicely provide artificial gravity for the
astronauts. That ship would reach Alpha Centauri in five years'
Earth-time while only a bit over two years would elapse in ship-
time. In eleven years' ship-time it could reach the center of our
galaxy. But during that time, almost 27,000 years would have
passed on Earth. In fifteen years' ship-time the astronauts could
reach Andromeda, 2.4 million light-years away
. By then, since
most of the trip was at near the speed of light relative to Earth,
2.4 million years would have gone by back on Earth. After expe-
riencing the passage of twenty-three years, the astronauts would
actually pass the edge of the universe currently observable from
Earth, but 13.7 billion years would have elapsed in the reference

-

maxdancona

3
Tue 10 Nov, 2015 11:30 am
@oristarA,
For "ship-time" the observer is on the space ship. The distance is measured by the observer on the ship. The velocity is measured by the observer on the ship. There is no conversion needed.

It's just D = rt.

3
Tue 10 Nov, 2015 11:39 am
@oristarA,
You need to use the lorentz calculation to calculate time difference between traveler and observer.

There is a time dilation calculator here -
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html
0 Replies

McTag

-1
Tue 10 Nov, 2015 12:12 pm

It's a mistake. Miles, not light years.
Tes yeux noirs

4
Tue 10 Nov, 2015 12:39 pm
@McTag,
Quote:
It's a mistake. Miles, not light years.

If you mean the distance to Andromeda, the most recent estimate is 2.51 million light-years ± 0.13 million light-years.
0 Replies

layman

0
Tue 10 Nov, 2015 12:55 pm
@oristarA,
Don't be fooled by these glib answers, Ori. This is just another absurdity created by abandoning all standards.

If a ship is constantly accelerating at 1g then it will reach the speed of light in a little less than a year. For it to just keep on accelerating after that, it would have to exceed the speed of light, which is supposedly impossible.

One "gimmick" is to say it won't "look" that way to people on earth. No matter how fast it is going, we will never "see" it to be faster than the speed of light. "Appearance" becomes reality, for those with no sense of reality.

The same absurdity applies to the ship. It too will never reach the speed of light from it's perspective. For this reason it could will never "see" itself as exceeding the speed of light. It can go 13.7 billions light years in just 23 years, or so it says:

Quote:
After experiencing the passage of twenty-three years, the astronauts would actually pass the edge of the universe currently observable from Earth, but 13.7 billion years would have elapsed in the reference frame of a long-dead Earth.

When you're constantly changing standards for MEASURING space and time, then there is no standard whatsoever. There are no limits whatsoever.

So if we say we "see" light from 13.7 billions years ago, that could only be 23 years in "reality." Which means we could never know how far away it "really" is (how far it really travelled), because whatever speed it's travelling at (how much distance it has covered in how much time) has NOTHING to do with how we measure it. We will measure it as always being the same (186,000 miles per second), regardless.

Note also that using the word "see" here means nothing. It is not something we "see" with our eyes. It is a mental conclusion strictly deduced mathematically from presupposed premises.
layman

0
Tue 10 Nov, 2015 02:10 pm
@layman,
Oris, there is a lot of incoherent nonsense that is spouted by people opining on this topic. Believe me, I know. I started a thread on special relativity (since deleted in it's entirety) which ran about 200 pages before being deleted.

But understanding the premises helps you see the problem. All these calculations are made with the assumption that whatever object you're doing the measuring from is motionless. Earth residents presuppose that they are motionless, for example. Meanwhile, those on the spaceship ALSO assume they are motionless when undertaking to measure time and distance. Can they both "really" be motionless, ya figure? Note that is has already been posited that the spaceship is "constantly accelerating."
0 Replies

maxdancona

3
Tue 10 Nov, 2015 03:58 pm
@maxdancona,
I didn't pay attention to the question... what makes this interesting is the acceleration from rest in Earth's frame of reference, to the travelling speed of near the speed of light (again from Earth's frame).

From the ships frame of reference, the distance would be much shorter, if it weren't for the fact that the ship had to accelerate, the problem would be much less interesting.

This like explains it pretty well.

http://physics.stackexchange.com/questions/109776/how-long-would-it-take-me-to-travel-to-a-distant-star
layman

-1
Tue 10 Nov, 2015 04:10 pm
@maxdancona,

It doesn't "explain" anything, Oris. I don't know how interested you are in phsyics. If you're simply looking for a math formula, this site seems to have part of it. If you're looking for an actual "explanation," then not so much.
maxdancona

4
Tue 10 Nov, 2015 04:13 pm
@layman,
Quote:
If you're simply looking for a math formula, this site seems to have part of it. If you're looking for an actual "explanation," then not so much.

We have already had this discussion. If you go to University and take Physics courses, you will learn that the mathematical function is the explanation.

You seem to reject this idea... which is ok. But I am pretty sure that our friend Oristar is looking for the Physics answer as taught in University and understood by Physicists.
layman

-1
Tue 10 Nov, 2015 04:22 pm
@maxdancona,
Quote:
If you go to University and take Physics courses, you will learn that the mathematical function is the explanation.

Naw, I won't "learn" that, although I might be told that. I wouldn't take a Physics course to find a "mathematical" explanation. I would expect a physical explanation.
0 Replies

Setanta

3
Tue 10 Nov, 2015 04:43 pm
0 Replies

layman

-1
Tue 10 Nov, 2015 04:47 pm
@maxdancona,
From the site you cited, Max:

Quote:
you might wonder how the spaceship accelerating at 1g can travel 490 light years in 12.1 years if nothing can travel faster than light. The answer is that the spaceship doesn’t travel 490 light years - the Lorentz contraction caused by its high speed means it travels a much shorter distance.

How does it "travel" a shorter distance than it is? Does space shrink? Here's one way to look at it: If the people on the spaceship "calculate" how long a unit of measurement, say a yardstick, would be on earth, compared to it's own, the earth's yardstick would be VERY short by comparison. The yardstick on their ship might be 50 earth miles long.

All this "calculation" is of course based on unproven and disputed assumptions about the nature of time and length in the physical world, but let's leave that issue aside for now.

So, how far away is the object they are destined for? Using their own 50-mile long yardstick, it will only be so many "yards," eh? But it's the same space, either way. It's just being measured with a different standard (a 50-mile long "yardstick"). The space hasn't "shrunk." It's the same space, for either earth, or the ship.

This all works perfectly for MATH purposes. Everything "adds up." But from a physical standpoint, the "explanation" doesn't explain anything at all.
maxdancona

4
Tue 10 Nov, 2015 07:14 pm
@layman,
Layman,

I can give you the mathematical answer taught in University physics class and accepted by Physicists. Or better yet, I can point you to the link on Lorentz contraction.

If you aren't going to accept the official physics answer, I don't know if a discussion on the topic will be very interesting or productive to either of us.

Would you like the correct answer (according to the accepted understanding of Physics)? This isn't something to debate-- there is a correct answer that is well understood and agreed upon by physicists everywhere. The basic concepts of relativity have been proven and they aren't disputed by anyone who understand the mathematics.

layman

-1
Tue 10 Nov, 2015 07:34 pm
@maxdancona,
Quote:
The basic concepts of relativity have been proven and they aren't disputed by anyone who understand the mathematics.

I thought we just went through this. Did you ever do the research to get the CORRECT answer about special relativity being "proven?"

Apparently not. Learn some physics, Max.
maxdancona

4
Tue 10 Nov, 2015 07:48 pm
@layman,
It has been proven multiple times in various ways.

It has been proven with satellite studies, with atomic clocks on planes and towers, with predictions about subatomic particles (specifically pi-mesons). It has been proven with orbital calculations. And, it has been used to predict astronomical observations (which have matched the predictions). In each of these cases the predictions matched the measurements and all other explanations were disproved.

I don't know why you insist on rejecting what is now basic accepted science (as understood by the scientific community). To say that it hasn't been tested and proven is simply incorrect.

layman

-1
Tue 10 Nov, 2015 08:00 pm
@maxdancona,
Quote:
To say that it hasn't been tested and proven is simply incorrect.

Like I said, Max, you would do yourself a favor if you would just learn up on the concepts (and I don't mean math) underlying theories of relative motion. You wouldn't run around embarrassing yourself in this way if you did.

The are theories of relative motion which have radically different fundamental premises from SR, but which have also been confirmed by all the very same experiments which "confirm" SR. Have those theories been "proven" too, ya figure?
0 Replies

layman

-1
Tue 10 Nov, 2015 08:39 pm
@maxdancona,
Quote:
I can give you the mathematical answer taught in University physics class and accepted by Physicists. Or better yet, I can point you to the link on Lorentz contraction.

Are you even aware, Max, that Henrik Lorentz created the Lorentz transformation (used in SR) many years before Al introduced his theory in 1905? Are you aware that Al "stole" those transformations from a theory of relative motion that posited absolute simultaneity rather than relative simultaneity and that his theory, with some minor modifications is still valid today?

Needless to say, Lorentz was quite aware of the "Lorentz contraction" that you want to point me to. His theory would say that it's impossible to go 13.7 light years in 23 years without exceeding the speed of light. However, his theory would NOT say that it's impossible to exceed the speed of light. His theory would, unlike SR, also deny that the speed of light is isotropic (as the GPS system has shown--i.e, that it is anisotropic). His theory does NOT say that the 'lorentz contraction" is reciprocal--i.e., he would not make the absurd claim that SR does to the effect that "each yardstick is shorter than the other." Check it out sometime, eh?

The Lorentz transformations do NOT tell you how they should be applied. They tell you, for example, that a moving clock runs slower than a stationary one, but math cannot tell you which of two objects (say a car and the road it's on) is moving. Theory must tell you that, and then the theory tells you how to apply the math. The math doesn't, and can't, tell you what the theory is.

You should know these things if you want to run around playing the role of a physics expert, as you do here.
maxdancona

4
Tue 10 Nov, 2015 08:42 pm
@layman,
Yes, of course I am aware. We are taught this is Physics class, along with the challenges presented by Maxwell's equations and the Michelson-Morley experiment.

There was a process that lead to the development of special relativity around the turn of the century. Einstein didn't just make it up in a vacuum. The mathematics of special relativity were developed using previous work... they were the solution to a set of intriguing problems that were being contemplated around the turn of the century. These ideas were already around waiting for someone to put them together, Einstein happened to be the one.

Anyway, this discussion is getting boring... probably for both of us. Let's end it here.

I am pretty sure that Oristar got the answer he was looking for.

layman

-1
Tue 10 Nov, 2015 08:58 pm
@maxdancona,
Quote:
Let's end it here.

OK. I will just make one last correction concerning this post of yours. You say:

Quote:
These ideas were already around waiting for someone to put them together, Einstein happened to be the one.

This is inaccurate. The ideas HAD already been "put together" before Einstien, and they were put together in a way that is still theoretically valid today. There just weren't "put together" in the same way Al did. Since they weren't, all the many "paradoxes" of SR (such as the "twin paradox") don't arise in them. They don't require, as SR does, different observers to make contradictory claims in order for the theory to work.

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