The dumb questions thread

[Wiploc]

View attachment 21377

My new theory is that they took the picture from underneath.

 

[Jimmy Higgins]

So I was pondering about faster than light speed travel. And two questions came to mind (ignoring whether FTL speed is possible).

1) Can you steer when going faster than light? (I suppose this applies to any really fast speed approaching a fraction of c)
Someone showed me a YouTube link about using a blackhole's gravity to slingshot a laser around it, to hit your ship and go very very fast. I had a few concerns about that, but the one I'm asking about is vectors. If you are going really really really fast... is it possible to modify your trajectory? We are struggling with theories about how to change the course of a meteor heading towards earth at pathetically low speeds relative to light. So I was wondering, you shoot yourself into a direction at a mammoth speed... is your trajectory set in stone? How can you apply any force in a lateral direction to change your trajectory?

2) Can you navigate when going faster than light? When you go faster than light, doesn't light do the Star Trek thing, kind of like how water drops appear to be going horizonal when you drive the car? It might be as simple as some math, but from an engineering point of view, wouldn't it be hard to know where you are exactly when going faster than light? Yes, you have velocity (though to what precision) and time, but is there certainty in direction? Is it also possible to use stars for navigational beacons when going faster than light?

 

[thebeave]

Post a link, or an image of an upside down crater, if you would.

Here's the first footprint on the moon. Since I was a little kid, I've always thought it was weird, because it looks inverted, but I never heard anyone else mention it or give an explanation for it. I guess its the same effect we're discussing here?

 

[bigfield]

So I was pondering about faster than light speed travel. And two questions came to mind (ignoring whether FTL speed is possible).

1) Can you steer when going faster than light? (I suppose this applies to any really fast speed approaching a fraction of c)
Someone showed me a YouTube link about using a blackhole's gravity to slingshot a laser around it, to hit your ship and go very very fast. I had a few concerns about that, but the one I'm asking about is vectors. If you are going really really really fast... is it possible to modify your trajectory? We are struggling with theories about how to change the course of a meteor heading towards earth at pathetically low speeds relative to light. So I was wondering, you shoot yourself into a direction at a mammoth speed... is your trajectory set in stone? How can you apply any force in a lateral direction to change your trajectory?

You can't travel faster than light. c is a fundamental speed limit. You can't just ignore that.

If you are travelling at a fraction of c, acceleration still works the same way as it does at low speeds. If you rely on Newton's third law and use a rocket engine, you'll need a very large amount of ejection mass in order to change your trajectory by any meaningful amount. In practice, you would probably want to point yourself in the right direction before you start accelerating, rather than wasting your thrust travelling in the wrong direction.

The reason it's hard to shift a meteor is because a meteor has a lot of mass, therefore a lot of inertia, and it's hard to attach a thruster that's big enough and lasts long enough to impart any meaningful acceleration on it.

2) Can you navigate when going faster than light? When you go faster than light, doesn't light do the Star Trek thing, kind of like how water drops appear to be going horizonal when you drive the car? It might be as simple as some math, but from an engineering point of view, wouldn't it be hard to know where you are exactly when going faster than light? Yes, you have velocity (though to what precision) and time, but is there certainty in direction? Is it also possible to use stars for navigational beacons when going faster than light?

Sci Fi relies on adding extra rules to the universe, like wormholes and hyperspace. If you want to know how physics works in these universes, you have to read the fictional source material or ask the creators.

Faster than light travels breaks the rules of relativity so badly that you descend into absurdities pretty quickly. Spaceships travelling faster than c would somehow have negative mass, experience time in reverse, see everything back to front and upside down, and everyone on board would have green skin and goatees.

 

[skepticalbip]

I always enjoy FTL travel. It saves me the hassle and worry of being late because every time I travel FTL I always get to where I am going before I start out.

 

[George S]

So I was pondering about faster than light speed travel. And two questions came to mind (ignoring whether FTL speed is possible).

1) Can you steer when going faster than light? (I suppose this applies to any really fast speed approaching a fraction of c)
Someone showed me a YouTube link about using a blackhole's gravity to slingshot a laser around it, to hit your ship and go very very fast. I had a few concerns about that, but the one I'm asking about is vectors. If you are going really really really fast... is it possible to modify your trajectory? We are struggling with theories about how to change the course of a meteor heading towards earth at pathetically low speeds relative to light. So I was wondering, you shoot yourself into a direction at a mammoth speed... is your trajectory set in stone? How can you apply any force in a lateral direction to change your trajectory?

There is one FTL in which the spaceship distorts space itself so the space behind ages faster than that in front. The spaceship never exceeds c in space; it need not move at all in space. However, the spaceship may appear to an observer to have reached its destination faster than light which did not also go through the distorted patch in space. This method "warps" space and is, therefore, a "warp drive." If one of the paths -- your slingshot around a massive object -- from A to B (as in an Einstein Ring) did not have the warped space you could see your spaceship before you turned the warp drive on viewing on a different path.

2) Can you navigate when going faster than light? When you go faster than light, doesn't light do the Star Trek thing, kind of like how water drops appear to be going horizonal when you drive the car? It might be as simple as some math, but from an engineering point of view, wouldn't it be hard to know where you are exactly when going faster than light? Yes, you have velocity (though to what precision) and time, but is there certainty in direction? Is it also possible to use stars for navigational beacons when going faster than light?

Navigation would involve changing the direction of the distortion -- a technology requirement to get the direction of the warp in the first place. The Star Trek visual effect would not happen.

____________
Gravity happens for exactly that reason.

[YOUTUBE]gcvq1DAM-DE[/YOUTUBE]

But also see (by same physicist).

[YOUTUBE]qhVgIW4_-AQ[/YOUTUBE]

 

[Wiploc]

Post a link, or an image of an upside down crater, if you would.

Here's the first footprint on the moon. Since I was a little kid, I've always thought it was weird, because it looks inverted, but I never heard anyone else mention it or give an explanation for it. I guess its the same effect we're discussing here?

View attachment 22002

It looks right to me. But if you perceive the light as coming from the left, then it should be inverted for you.

 

[Wiploc]

Post a link, or an image of an upside down crater, if you would.

Here's the first footprint on the moon. Since I was a little kid, I've always thought it was weird, because it looks inverted, but I never heard anyone else mention it or give an explanation for it. I guess its the same effect we're discussing here?

View attachment 22002

It looks right to me. But if you perceive the light as coming from the left, then it should be inverted for you.

Ah, I got it! Right now it looks like it's sticking up out of the ground. And, yes, I'm seeing the light as from the left.

 

[steve_bank]

High speed space travel is problematic if you are in what we would call normal space.

The structural reaction forces in the structure for turns or stops would be enormous. I expect the result would also be heat.
STNG got around it with 'structural integrity fields' and 'inertial dampers'. I giggle a bit whenever Picard orders 'full stop'.

Heat rejection on the shuttles and on the ISS are problematic even with the relatively small loads. The only way to reject heat is radiation. The shuttles could not stay up if the cargo bay doors were not opened exposing radiators.

Whatever space ship is created, the propulsion will mot be 100% efficient and a lot of heat would be created.

Even at 99.999999 % efficiency the terawatt generator on Enterprise would cook the crew. A ship in space is like a Thermos vacuums bottle.


There is a theory of FTL that creates a bubble around the ship such that the ship appears to not go fast. The problem in the theory it needs energy with a negative sign.

There is also the problem of non empty space. There are pictures of micrometeorite damage on the space shuttles. Dust and gas would abrade the ship as speed increased.

 

[Wiploc]

1) Can you steer when going faster than light? (I suppose this applies to any really fast speed approaching a fraction of c)
... If you are going really really really fast... is it possible to modify your trajectory? We are struggling with theories about how to change the course of a meteor heading towards earth at pathetically low speeds relative to light. So I was wondering, you shoot yourself into a direction at a mammoth speed... is your trajectory set in stone? How can you apply any force in a lateral direction to change your trajectory?

All motion is relative. You are always stopped relative to yourself. Your controls will always seem normal to you. Even though you are traveling very near to c relative to, say, a cosmic ray, your handles normally. It is not affected by its speed relative to other objects.

But suppose we look at your vehicle from another point of view, rather than from your own. Suppose you start from the earth, and accelerate until you are at .99 c relative to the earth. And suppose you want to reach .995 c (again, relative to the earth). If you are watching from inside your ship, acceleration will seem normal. But if we are watching from earth, your acceleration will seem slow and costly.

But, of course, that's nothing new. That's how it looks now--as viewed by a cosmic ray--when you accelerate your car.

If there are tachyons around, you can still maneuver your car normally, even though you are going faster than light relative to the tachyon.

Now suppose you are traveling at 1.5 c, relative to the local stars, and you discover that you are heading right at one, and there is no way you can slow down in time to avoid it. You can still turn. The relativistic distortions are in the direction of relative travel. So even though you can't effectively brake, you still ought to be able to turn normally. Because your speed to the right or left of the obstacle is zero, which isn't fast enough to generate relativistic distortions.

2) Can you navigate when going faster than light? When you go faster than light, doesn't light do the Star Trek thing, kind of like how water drops appear to be going horizonal when you drive the car? It might be as simple as some math, but from an engineering point of view, wouldn't it be hard to know where you are exactly when going faster than light? Yes, you have velocity (though to what precision) and time, but is there certainty in direction? Is it also possible to use stars for navigational beacons when going faster than light?

Let's do an analogy with water waves. Suppose waves travel at (to make up a number) two miles an hour. And suppose you're in a boat going four miles an hour. Do you still encounter waves even though you're going faster than them? Yes. You keep striking (or being struck by) waves no matter what speed or direction you go. (Unless you match speed and direction with the waves.)

So, yes, you can still learn from the waves anything that you could learn from them if you were stopped relative to the shore.

Now if we consider light, there is no such thing as matching its direction and speed. So you'll still encounter peaks and troughs (or photons, if you prefer) so you can still see things.

 

[steve_bank]

If you are traveling at 0.9 C in the frame of your ship you have to deal with inertia and momentum if you turn.

 

[bilby]

... Now suppose you are traveling at 1.5 c, relative to the local stars, and you discover that you are heading right at one ...

How would you discover this?

Even leaving aside the fact that your maximum velocity relative to ANY frame is c, how would the information about the star's existence in your path reach you, before you had hit it?

 

[Wiploc]

... Now suppose you are traveling at 1.5 c, relative to the local stars, and you discover that you are heading right at one ...

How would you discover this?

I don't know what you think the problem is.

So I'll take a guess, and you can tell me if I got it right.

Let's take a star with no proper motion (as viewed from your ship). If the star is moving (relative to your ship) it is moving directly towards or away from you.

The star is shining, so we can detect it with our eyes, and cameras, and radio telescopes, and so on.

The star has been shining for a long time, so between you and star is a beam of photons. If you could instantly teleport to any place between you and the star, you would still see it. There are photons in every place between you and the star.

In a boat that goes faster than waves, you still encounter waves, and in a ship that goes faster than light, you still encounter light.

If I'm guessing wrong here, you're going to have to tell me what the issue is that I'm failing to address.

So, let's start you off as stopped relative to the star. At that point, you can see the star.

Now you accelerate toward the star. Light shifts blue, but you can still see the star.

Eventually, as you continue to accelerate, the light from the star would be so energetic that it would burn out cameras, or melt your ship, or what have you. But, as the question has to do with a faster-than-light spaceship, I think we have to assume that such problems have been coped with somehow, in some science fiction manner. If not, then the part of your ship that is melting is the direction that the star in in; you're still detecting the star.

When you get fast enough, the entire visible spectrum shifts beyond the visible spectrum. But other light shifts into the visible spectrum. And you have instruments which detect that light.

It isn't like there isn't light there. You're just running into it really hard. Which makes it hard to ignore. You can't not see the star.

Now we can't actually reach c. We've known this since Einstein. But we can approach c. And as we approach c, there is no point where we run out of photons and can't see the star. The photons are there, and they're hard to ignore.

Maybe we can exceed c somehow? I don't know. Maybe you'd have to have started as tachyons, and made your ship out of tachyons. Or maybe there's some sci-fi device that lets you jump c once you get close enough.

In any case, since the question is about faster than light travel, let's assume that there is somehow a faster than light ship heading for that star. Can it detect the star? Yes, the photons are there, and they are hitting the ship even harder than before. I assume they move at light speed relative to the hyperluminal ship, the same as they do for anything else.

Maybe, by this time, no light from the star is in the visible range. But it's still there, and it's still energetic, and still detectable by our science fiction instruments.

Or maybe none of that's relevant to your question. Maybe you're worried about how the light can get to you in time for you to see it.

So lets start you off 100 light years from the star. You're looking at light that was emitted 100 years ago. After you travel fifty light years closer, you'll be seeing light that was emitted fifty years ago. If you travel that fifty light years in a mere ten minutes, that doesn't affect your result. No matter how fast you're going, when you get to the fifty light year location, you'll be seeing light that is fifty years old.

I hope that helps. I hope something I've said helps. If not, then it's up to you to explain what your question is, because I'm done guessing.

 

[bilby]

... Now suppose you are traveling at 1.5 c, relative to the local stars, and you discover that you are heading right at one ...

How would you discover this?

I don't know what you think the problem is.

So I'll take a guess, and you can tell me if I got it right.

Let's take a star with no proper motion (as viewed from your ship). If the star is moving (relative to your ship) it is moving directly towards or away from you.

The star is shining, so we can detect it with our eyes, and cameras, and radio telescopes, and so on.

The star has been shining for a long time, so between you and star is a beam of photons. If you could instantly teleport to any place between you and the star, you would still see it. There are photons in every place between you and the star.

In a boat that goes faster than waves, you still encounter waves, and in a ship that goes faster than light, you still encounter light.

If I'm guessing wrong here, you're going to have to tell me what the issue is that I'm failing to address.

So, let's start you off as stopped relative to the star. At that point, you can see the star.

Now you accelerate toward the star. Light shifts blue, but you can still see the star.

Eventually, as you continue to accelerate, the light from the star would be so energetic that it would burn out cameras, or melt your ship, or what have you. But, as the question has to do with a faster-than-light spaceship, I think we have to assume that such problems have been coped with somehow, in some science fiction manner. If not, then the part of your ship that is melting is the direction that the star in in; you're still detecting the star.

When you get fast enough, the entire visible spectrum shifts beyond the visible spectrum. But other light shifts into the visible spectrum. And you have instruments which detect that light.

It isn't like there isn't light there. You're just running into it really hard. Which makes it hard to ignore. You can't not see the star.

Now we can't actually reach c. We've known this since Einstein. But we can approach c. And as we approach c, there is no point where we run out of photons and can't see the star. The photons are there, and they're hard to ignore.

Maybe we can exceed c somehow? I don't know. Maybe you'd have to have started as tachyons, and made your ship out of tachyons. Or maybe there's some sci-fi device that lets you jump c once you get close enough.

In any case, since the question is about faster than light travel, let's assume that there is somehow a faster than light ship heading for that star. Can it detect the star? Yes, the photons are there, and they are hitting the ship even harder than before. I assume they move at light speed relative to the hyperluminal ship, the same as they do for anything else.

Maybe, by this time, no light from the star is in the visible range. But it's still there, and it's still energetic, and still detectable by our science fiction instruments.

Or maybe none of that's relevant to your question. Maybe you're worried about how the light can get to you in time for you to see it.

So lets start you off 100 light years from the star. You're looking at light that was emitted 100 years ago. After you travel fifty light years closer, you'll be seeing light that was emitted fifty years ago. If you travel that fifty light years in a mere ten minutes, that doesn't affect your result. No matter how fast you're going, when you get to the fifty light year location, you'll be seeing light that is fifty years old.

I hope that helps. I hope something I've said helps. If not, then it's up to you to explain what your question is, because I'm done guessing.

As you approach c relative to the star, the light from the star (even the really long radio waves) is blue-shifted to gamma. It's going to pass through a mile of depleted uranium shielding practically unchanged - how would you detect such hugely energetic, super high frequency gammas?

But there's a bigger problem - why are you surprised that you are pointing at the star? Surely you knew it was there to begin with. But having accelerated "beyond" c, you have given yourself less than no time to steer - at 1.5c, you hit the farthest away stuff on your trajectory first.

Presumably.

Fucked if I know what happens at tachyonic velocities. I'm just guessing

 

[Loren Pechtel]

... Now suppose you are traveling at 1.5 c, relative to the local stars, and you discover that you are heading right at one ...

How would you discover this?

Even leaving aside the fact that your maximum velocity relative to ANY frame is c, how would the information about the star's existence in your path reach you, before you had hit it?

You can still look forward even if you're going FTL. (Now, whether your optics can work is another matter...) You get the same starbow effect of relativistic velocity except even more so.

Now, if something appears in your path that's another matter, you're not going to see it.

 

[Loren Pechtel]

As you approach c relative to the star, the light from the star (even the really long radio waves) is blue-shifted to gamma. It's going to pass through a mile of depleted uranium shielding practically unchanged - how would you detect such hugely energetic, super high frequency gammas?

But there's a bigger problem - why are you surprised that you are pointing at the star? Surely you knew it was there to begin with. But having accelerated "beyond" c, you have given yourself less than no time to steer - at 1.5c, you hit the farthest away stuff on your trajectory first.

Presumably.

Fucked if I know what happens at tachyonic velocities. I'm just guessing

No. It's not going to be blue-shifted to gamma. At 1.5c you're hitting the waves at 2.5x the rate you would if you're standing still. Visible light isn't going to be shifted beyond the near ultraviolet by that kind of speed. You're going to need something over 100,000c to shift visible light into the gamma part of the spectrum.

 

[bilby]

 

[Wiploc]

... Now suppose you are traveling at 1.5 c, relative to the local stars, and you discover that you are heading right at one ...

How would you discover this?

Even leaving aside the fact that your maximum velocity relative to ANY frame is c, how would the information about the star's existence in your path reach you, before you had hit it?

You can still look forward even if you're going FTL. (Now, whether your optics can work is another matter...) You get the same starbow effect of relativistic velocity except even more so.

Now, if something appears in your path that's another matter, you're not going to see it.

I'm not sure what you're saying, so I'll create a hypothetical to see if it illuminates things for us.

Suppose you are 100 light years from point X, and headed towards point X at 2c, and at this moment, a mime in an actual glass box teleports to point X.

Question: Will you see the mime in time to evade?

First answer: You will see the mime when you are 33 light years from X. You'll move 66 light years while the light from the mime moves 33.

Objection to first answer: I don't even know whose point of view I'm talking about. Let's try to establish a point of view, and see what that looks like.

Suppose we're you, in your point of view. We think we're stopped, right, because everything is stopped relative to itself. And the light from X is blue-shifted, but still moving at c, relative to us.

But X itself is approaching at 2c, ahead of it's light. Its light trails behind it like the wake of a fast boat. And you can't detect the boat by feeling its wake, because the boat gets to you ahead of the wake.

At last, I understand why people think you can't see at superluminal speeds.

But, yes, the mime has to teleport in front of you for this to work? Otherwise there would be a beam of light ahead of her that you could see?

I think that works if you were moving slowly relative to the mime early on. I'm not sure it works if the mime has always been approaching at 2c.

 

[Bomb#20]

No. It's not going to be blue-shifted to gamma. At 1.5c you're hitting the waves at 2.5x the rate you would if you're standing still. Visible light isn't going to be shifted beyond the near ultraviolet by that kind of speed. You're going to need something over 100,000c to shift visible light into the gamma part of the spectrum.

You're describing the ship/light interaction from the point of view of the star. What you're actually going to experience will be from the point of view of the ship, and that means the whole universe is foreshortened and the waves along with it. At c the wavelength is foreshortened to zero and the blue shift is infinite. God knows how foreshortened they are at 1.5c.

 

[Bomb#20]

Now, if something appears in your path that's another matter, you're not going to see it.

I'm not sure what you're saying, so I'll create a hypothetical to see if it illuminates things for us.

Suppose you are 100 light years from point X, and headed towards point X at 2c, and at this moment, a mime in an actual glass box teleports to point X.

Question: Will you see the mime in time to evade?

First answer: You will see the mime when you are 33 light years from X. You'll move 66 light years while the light from the mime moves 33.

Objection to first answer: I don't even know whose point of view I'm talking about. Let's try to establish a point of view, and see what that looks like.

Sounds like you're talking about point X's point of view.

Suppose we're you, in your point of view. We think we're stopped, right, because everything is stopped relative to itself. And the light from X is blue-shifted, but still moving at c, relative to us.

But X itself is approaching at 2c, ahead of it's light. Its light trails behind it like the wake of a fast boat. And you can't detect the boat by feeling its wake, because the boat gets to you ahead of the wake.

At last, I understand why people think you can't see at superluminal speeds.

Sure, but it's a reasoning error. The assumption that relative to you the light from X is approaching you at c is based on the premise that relativity is true. The assumption that you're headed towards point X at 2c is based on the premise that relativity is false. You need to use consistent premises. That means if you want to figure out what will happen if you're approaching X at 2c, you need to discard Special Relativity and switch to Lorentz Ether Theory. In LET, superluminal observers aren't going to observe light always traveling at c.

I think that works if you were moving slowly relative to the mime early on. I'm not sure it works if the mime has always been approaching at 2c.

The mime isn't approaching you at all. You're approaching the mime. The principle that those are the same thing goes away in LET.