Thread: Light Speed

My name's Ross. I love astronomy, but I'm still a novice.

I've heard people say that it's not possible to travel to the otherside of the galaxy because if you were in a space ship that was traveling at near the speed of light, you would only be able to travel 50 or 60 light years from Earth in a lifetime. My question is... Due to special relativity and time dilation, couldn't one theoretically travel several hundred thousand light years from Earth, but for an observer on Earth only 50 or 60 years would have passed? What's the ratio, for example: If a man travels at near the speed of light for 10 years (according to him), how many years would have passed on Earth?

Originally Posted by Made of Stardust

My name's Ross. I love astronomy, but I'm still a novice.

I've heard people say that it's not possible to travel to the otherside of the galaxy because if you were in a space ship that was traveling at near the speed of light, you would only be able to travel 50 or 60 light years from Earth in a lifetime. My question is... Due to special relativity and time dilation, couldn't one theoretically travel several hundred thousand light years from Earth, but for an observer on Earth only 50 or 60 years would have passed? What's the ratio, for example: If a man travels at near the speed of light for 10 years (according to him), how many years would have passed on Earth?

It's the other way around. Thousands of years may have passed on earth, while the traveler only experiences the passing of 10 years.

That's exactly what I said. Can someone please give me an intelligent answer?

Originally Posted by Made of Stardust

Can someone please give me an intelligent answer?

timedial.gif

You got it.

Cool! I'm assuming t=Time and c=The speed of light in a vacuum. What does v stand for? Is it velocity?

Also, I know that the speed of light is not an arbitrary number, rather it's a fundamental property of the Universe. Why is the speed of light connected/related to mass-energy equivalence?

Also, is it true that everything in the Universe travels at exactly the speed of light through SPACETIME? Ex. let 10 represent the speed of light in a vacuum. If a man is traveling through space at a speed of 2, then he is traveling through time at a speed of 8. Or, if a man is traveling through space at a speed of 6, then he is traveling through time at a speed of 4. It always equals 10.

Please post actual questions as a new thread in the appropriate forum. It makes it easier to keep questions straight and on topic as well as it makes them much more visible for folks that are somewhat knowledgeable to see them and give some contribution.

The Equation is the Lorentz Contraction mod.
"t" is the rest length
"t ^ 1" Is observed length
You know what "c" is and "v" is velocity.

Originally Posted by Made of Stardust

Also, I know that the speed of light is not an arbitrary number, rather it's a fundamental property of the Universe. Why is the speed of light connected/related to mass-energy equivalence?

And you've essentially asked what E=mc^2 means.
Try reading here: Mass

Originally Posted by Made of Stardust

Also, is it true that everything in the Universe travels at exactly the speed of light through SPACETIME? Ex. let 10 represent the speed of light in a vacuum. If a man is traveling through space at a speed of 2, then he is traveling through time at a speed of 8. Or, if a man is traveling through space at a speed of 6, then he is traveling through time at a speed of 4. It always equals 10.

Asking if something is "true" is a misleading question.
You can ask if a theory truly states, "such and such" but unless a theory is proven beyond all doubt to be true- you cannot ask if something is "true."
Remember: A hypothesis is an unsupported idea (What people commonly misrefer to as a theory) and a Theory is a model that has been observed as in concordance with supportive evidence.
Because theories tend to be well supported by observational evidence, it's too easy to slip into considering them as 'true.' But that's unscientific.
They are models of reality and are never proven to be true since you cannot prove that they AREN'T an illusion- You cannot prove a negative. They are simply models that are constantly tested and observed in order to make them as accurate as possible.

Now, as to the actual question: The short answer is yes they are proportional and the long answer is no, your example is way off. They are proportional but exponential.
It's related to the above question and answer.
What you're asking about is the crux of Relativity as a theory and it really deserves its own thread for an in depth discussion.


ETA: Seems that although there is a laTeX editor offered- it doesn't work- or actually show up. Parsing doesn't seem to work right either...
Remind me to smack Tom upside the head later.

Originally Posted by Made of Stardust

Cool! I'm assuming t=Time and c=The speed of light in a vacuum. What does v stand for? Is it velocity?

In the expression,

is the dilated time [or time measured by Earth-bound clocks], is the proper time [or time measured by spacecraft-board clocks], is the speed of the spacecraft, and is the speed of light.

Assuming that the spacecraft has sufficient provisions for the voyage, there is no limit to how far it can take an astronaut crew. Generations of workers at mission control could communicate with the spacecraft as it wended its way toward the edge of the galaxy or beyond.

Remember, however, that the spacecraft cannot exceed the speed of light. To the crew, the galaxy would appear to zip past the spacecraft at a speed less than that of light. How does it ever travel to the edge of the galaxy within the lifetime of a single crew member? The flipside of time dilation is length contraction:

where is the contracted distance [as seen from the spacecraft] and is the proper length. What this means is that from within the spacecraft, the faster you go, the shorter the distance that you have to go.

However, you don't get something for nothing. The crew that returns to Earth after the journey will find a very different place than the one that they left. Owing to the nature of the journey, they may very well be international legends. However, all of their friends, family, and loved ones will have died decades earlier. The society to which they return will be as different from the one that they left as today's society is from the Middle Ages.

Thank you so much for the info! It is very much appreciated!!