Questions about the Speed of Light

[Turanil]

As most people in our western society, and probably everyone on these boards, I know that if a starship could travel at a speed close to that of light, time would pass much slower for it that it would pass for things immobile (or very slow). So, the starship for instance would travel a distance of two light years in three months of its own time, while two years passed on the planet it left (and the one it reaches).

But now comes the things on which I would like to be enlightened ( ):

1) If a thing would travel at exactly 100% the speed of light (despite it is theoretically impossible and would require infinite energy expenditure), would time slow so much as to stop altogether, meaning the starship ceases to age if even for only one nanosecond? Or does time still pass at the speed of light. (I hope my question is comprehensible)

Then, the related questions:

2) Supposing time still pass when at 100% the speed of light. Inside the starship that travels at 100% light speed, someone has to go from the back of the starship to the front. So, with regard to things immobile outside of the starship, he is moving slightly faster than the speed of light; so would it be impossible to walk forward in the starship?

3) Now, suppose time ceases to pass at exactly 100% of the speed of light. Fact is, a photon begins its travel from a star instantaneously at the speed of light; and then reaches a distant planet still at 100% of the speed of light. Between the moment when the photon was emited by the star, and the moment it reaches a planet, says that 5 years of local time have passed on said planet. However, since the photon travels at 100% light speed, no time at all passed for the photon. If indeed that is the case, at time 0 the photon is both at its point of departure and point of arrival 5 light-years-distance away. So the photon is simulateously at the same moment everywhere on the trajectory. Therefore, it could be said that subjectively the photon doesn't move at all, it exists in all places at the same moment. My question is that if I interpret things rightly, I wonder if there is not something extremely important lying there. Something about the nature of reality, of space and time itself, etc.

So, any comment from those with scientific backgrounds on ENworld?

Thanks.

 

[RangerWickett]

IANAPhysicist

If a ship were at the speed of light, time would not pass inside of it.

If a ship were at the speed of light minus 2 miles per hour, and a person inside of it tried to run at 3 miles per hour, he couldn't, because time slows down the closer they get to light speed. It would become impossible for him to run faster than 2 miles per hour, because while he thinks he's running at 3 miles per hour, to an outside observer it's taking him much longer to move that distance than he thinks. The faster he goes, the slower time moves for him, so he never gets a chance to move faster than light.

Here's the tricky part: relativity. Relativity says that the speed of light in a vacuum is always constant for any observer. The example I used to argue was, say you shoot two ships in opposite directions, each at 94,000 miles per second, slightly over 50% of the speed of light. Aren't they traveling faster than light, relative to each other?

The answer is no. Because of the nature of the universe, as you accelerate, you . . . I really don't know how to explain it well, but here I go.

Ship A and Ship B fly in opposite directions from Earth, each reaching a speed of 94,000 miles per second, relative to the Earth. The speed of light is 186,000 mps. Relative to ship A, your initial instinct is to say that Ship B is moving at 188,000 mps. But it's not, because time on ship A has slowed down to the point that it perceives ship B to moving at it's actual speed. Or so I believe. I might have misunderstood.

 

[Ambrus]

I just take comfort in the fact that somewhere, someone actually understands this stuff.

 

[Storminator]

As most people in our western society, and probably everyone on these boards, I know that if a starship could travel at a speed close to that of light, time would pass much slower for it that it would pass for things immobile (or very slow). So, the starship for instance would travel a distance of two light years in three months of its own time, while two years passed on the planet it left (and the one it reaches).

But now comes the things on which I would like to be enlightened ( ):

1) If a thing would travel at exactly 100% the speed of light (despite it is theoretically impossible and would require infinite energy expenditure), would time slow so much as to stop altogether, meaning the starship ceases to age if even for only one nanosecond? Or does time still pass at the speed of light. (I hope my question is comprehensible)

Then, the related questions:

2) Supposing time still pass when at 100% the speed of light. Inside the starship that travels at 100% light speed, someone has to go from the back of the starship to the front. So, with regard to things immobile outside of the starship, he is moving slightly faster than the speed of light; so would it be impossible to walk forward in the starship?

3) Now, suppose time ceases to pass at exactly 100% of the speed of light. Fact is, a photon begins its travel from a star instantaneously at the speed of light; and then reaches a distant planet still at 100% of the speed of light. Between the moment when the photon was emited by the star, and the moment it reaches a planet, says that 5 years of local time have passed on said planet. However, since the photon travels at 100% light speed, no time at all passed for the photon. If indeed that is the case, at time 0 the photon is both at its point of departure and point of arrival 5 light-years-distance away. So the photon is simulateously at the same moment everywhere on the trajectory. Therefore, it could be said that subjectively the photon doesn't move at all, it exists in all places at the same moment. My question is that if I interpret things rightly, I wonder if there is not something extremely important lying there. Something about the nature of reality, of space and time itself, etc.

So, any comment from those with scientific backgrounds on ENworld?

Thanks.

1) if you do get the speed of light, time in the accelerated frame stops according to the observations of the stationary frame. In the accelerated frame, time seems to pass as usual.

2) You can still move to the front of the space ship. As far as you can tell, the interior of the spaceship is stationary. The trick is to figure out what folks outside the ship see. And again he doesn't move faster than the speed of light. He moves at the speed of light.

3) There is defintely something supremely important there. This sort of reasoning completely upended all thoughts about physics when it first rolled around. The fact that it's not really all sorted out yet is testament to the power of those ideas.

One thing to consider: Our reality is really just a self-consistent set of rules for describing what we observe. Mathematics has shown that for any self-consistent set of rules, breaking one rule allows you to eventually break them all. Not reaching the speed of light is one of our rules. If you can break that rule, you should be able to, at some point or another, defy each and every rule of physics. That's why it's so hard to think these things thru. No matter where you turn you start running into contradictions, from which there is no escape.

PS

 

[KenM]

But is the speed of dark faster then the speed of light?

 

[Michael Morris]

As most people in our western society, and probably everyone on these boards, I know that if a starship could travel at a speed close to that of light, time would pass much slower for it that it would pass for things immobile (or very slow). So, the starship for instance would travel a distance of two light years in three months of its own time, while two years passed on the planet it left (and the one it reaches).

But now comes the things on which I would like to be enlightened ( ):

Division by 0 is undefined. You can see why if you graph out

f(x) = 1/x

Let's say that x is the speed difference between you and the speed of light. As x approaches 0, the slope gets steeper, and steeper, and steeper - but it never reaches the y axis, nor do we know where it would.

So the answers to all your questions are simply "undefined."

 

[Ycore Rixle]

Division by 0 is undefined. You can see why if you graph out

f(x) = 1/x

Let's say that x is the speed difference between you and the speed of light. As x approaches 0, the slope gets steeper, and steeper, and steeper - but it never reaches the y axis, nor do we know where it would.

So the answers to all your questions are simply "undefined."

Of course, then you get questions about tunneling through the barrier to some tachyonic state (since, in the heuristic example Michael mentions, 1/0 is undefined, but 1/[(-1)^(1/2)] is defined, if imaginary).

 

[babomb]

Disclaimer: I am a college student majoring in computer science, and it's been at least a year since I've studied relativity.

1) If a thing would travel at exactly 100% the speed of light (despite it is theoretically impossible and would require infinite energy expenditure), would time slow so much as to stop altogether, meaning the starship ceases to age if even for only one nanosecond? Or does time still pass at the speed of light. (I hope my question is comprehensible)

Well, maybe. Special relativity equations sort of break down at the speed of light, and you'd have to divide by zero. If you take the limit of the equation, however, the answer would be yes, time stops from the point of view of an observer. That may or may not have any meaning.

2) Supposing time still pass when at 100% the speed of light. Inside the starship that travels at 100% light speed, someone has to go from the back of the starship to the front. So, with regard to things immobile outside of the starship, he is moving slightly faster than the speed of light; so would it be impossible to walk forward in the starship?

Let's talk about what happens if the ship is moving at NEAR-light speed first. Let's say the ship is moving at 90% of the speed of light. And let's say the guy in the spaceship is moving at 5% of the speed of light. He is NOT moving at 95% of the speed of light relative to an outside observer. There is something called a Lorentz transformation involved. I'll spare you the equations, but an outside observer would say he was going just under 91% of the speed of light (10/11 of c, to be exact).

Why? Well, for the same reason that time dialates at high speeds (e.g., things on the ship appear to move more slowly), length CONTRACTS (the ship appears to be shorter in the dimension of its motion). That is, an outside observer would measure the ship as being shorter than if it were at rest. Here's a picture:

 ________          ____
|        |        |    |
|        |        |    |   --->
|x_______|        |x___|
Ship at rest     Ship moving to the right with repsect to observer

So, not only does the guy walking in the ship take longer to get to the other end, he moves a shorter distance (again, from the POV of an outside observer).

What happens AT the speed of light? Well, again, in the equations, you have to divide by zero. If we take the limit, we could say that time is stopped on the ship and that the ship has a length of 0. Assuming that were correct (and it isn't, since getting the ship to the speed of light is impossible to begin with), an outside observer would say that the man did not move at all relative to the ship.

3) Now, suppose time ceases to pass at exactly 100% of the speed of light. Fact is, a photon begins its travel from a star instantaneously at the speed of light; and then reaches a distant planet still at 100% of the speed of light. Between the moment when the photon was emited by the star, and the moment it reaches a planet, says that 5 years of local time have passed on said planet. However, since the photon travels at 100% light speed, no time at all passed for the photon. If indeed that is the case, at time 0 the photon is both at its point of departure and point of arrival 5 light-years-distance away. So the photon is simulateously at the same moment everywhere on the trajectory. Therefore, it could be said that subjectively the photon doesn't move at all, it exists in all places at the same moment. My question is that if I interpret things rightly, I wonder if there is not something extremely important lying there. Something about the nature of reality, of space and time itself, etc.

That's a good question, and one I can't adeqautely answer. The best I can do is say that I don't think the Special Relativity equations don't really apply to objects moving at the speed of light (whether general relativity is any more helpful, I don't know). The equations are, in a sense, derived from the postulate that the speed of light in a vacuum is constant, and so don't do a great job of describing motion OF light, if that makes any sense. They assume sub-light speed motion.

I'll also point out that simultanity is ALSO relative. However, I do not believe that the photon would see itself as existing along the entire path at once, because that would create difficulties in describing, e.g., the emission and absorbtion of photons by atoms. I could be wrong, but I point here as a reference: http://www.madsci.org/posts/archives/nov2000/975451454.As.r.html

 

[Turanil]

1/0 is undefined, but 1/[(-1)^(1/2)] is defined

Not sure I will sleep better to have learnt that though...

My main point was to reveal some major secret of the universe that has escaped the attention of the scientific community so far: at the speed of light time and space don't exist, and thus our universe is a vast holographic illusion with no substance. We believe the big-bang happened 14 billions years ago, but in fact it is the perpetual origin at every moment of that cosmic illusion we take for real. Of course, since all energy travels at the speed of light, and matter is just a state of energy, huh well... you see the point fallacy.

 

[Turanil]

I could be wrong, but I point here as a reference: http://www.madsci.org/posts/archives/nov2000/975451454.As.r.html

Thanks for the link. For one thing, my reasoning wasn't that idiot, as I see others have also pointed it out. Mmmmh... I believe that there must be something there! Only that the scientific community has not yet enough understanding to fathom about it. It also reminds me (if I remember well) something said by Stephen Hawkins, where he somewhat demonstrate that there is nothing before the big bang, as the universe is not a linear thing (a time infinity), but something that wraps unto itself. So, as asked by the student, the universe may well still be a singularity in a way beyond our comprehension.

All of this also brings the unanswerable questions: why something instead of nothing, and the reverse is also true: it is impossible to imagine nothingness (that is also the absence of empty space).

Oh my head...