Ask a physicist anything. (2)

[Wiccan_Child]

This thread was split automatically after 1000 replies and this thread has been automatically created.
The old thread automatically closed is here: "Ask a physicist anything."

 

[Wiccan_Child]

Hey, physicists.

So, I had an idea for a story running through my head and I wanted to ask a few physics related questions.

1. Let's say hypothetically some As Fast As Light (AFAL!) device grabs me by the wrist and near instantaneously accelerates to relativistic speeds. What happens to me? I'm assuming something like "you get torn apart at a sub-atomic level".

That depends on how it accelerated you. If it accelerated one part of you (you wrist, say), and the rest of you was pulled along by cellular bonds, then your wrist would be ripped out of your arm.

However, if you body was accelerated uniformly, then you would remain intact. That's why you can enter a supermassive blackhole, but not a normal black hole: in the former, the gravitational sheer is less, and your body experiences a more uniform acceleration.

2. I get vaguely the idea of "moving through time" and it needing its own dimension (axis). As one does anything time is ticking off. I'm not sure about the inverse relationship between speed and the speed of time (going faster means you move more slowly through time). Is this a basically a D=VT sort of thing? i.e., the more quickly you move the less time it takes to get to that distance? Or what's the relationship (in a nut shell).

Time dilation is experienced by those who observe others moving fast. Consider a spaceship moving away from Earth at a constant speed v. Someone on Earth would clocks on the ship ticking slower than clocks on Earth; that's time dilation.
Conversely, someone on the ship would see Earth's clocks ticking slowly.

So both observers see the other clocks ticking more slowly than theirs.

3. What basic sort of structural concerns are inherent in AFAL travel? I assume that you'd need some pretty seriously built space-ship. i.e., you'd need to make sure that everything got kept together. If the ship is moving AFAL, so are the passengers! How slowly would said ship have to accelerate to keep from pulling itself apart?

That depends on the material; a bubble of water would break apart very easily, but reinforced steel is somewhat stronger. But you cannot have AFAL travel by mere acceleration alone, at least according to a relativistic treatment of 'conventional' mechanics.

 

[Wiccan_Child]

Also, new thread! I feel like my sitcom has just got a spin-off. Ah, good times.

 

[AV1611VET]

I can see what you're about, but I don't understand it ...
I'm smiling because I'm exactly the 1000th and not because I posted 999 numbers before. And I think the 1058th time it should really begin to get boring?!

No offense meant here, but coming from someone who posts 0.26 posts per day (and there's nothing wrong with that) --- I can imagine 10 posts per day being boring to you, let alone 841.

 

[AV1611VET]

Also, new thread! I feel like my sitcom has just got a spin-off. Ah, good times.

Chrisbot will make you famous ---

 

[Cabal]

That depends on how it accelerated you. If it accelerated one part of you (you wrist, say), and the rest of you was pulled along by cellular bonds, then your wrist would be ripped out of your arm.

However, if you body was accelerated uniformly, then you would remain intact. That's why you can enter a supermassive blackhole, but not a normal black hole: in the former, the gravitational sheer is less, and your body experiences a more uniform acceleration.

Even uniform acceleration can kill if applied too quickly though, surely? Impulse would be a big factor still.

 

[gipsy]

2. I get vaguely the idea of "moving through time" and it needing its own dimension (axis). As one does anything time is ticking off. I'm not sure about the inverse relationship between speed and the speed of time (going faster means you move more slowly through time). Is this a basically a D=VT sort of thing? i.e., the more quickly you move the less time it takes to get to that distance? Or what's the relationship (in a nut shell).

My way of explaining this (at least to myself) is:
there are basically 2 dimensions: time and space, which you cross with a constant (combined) speed of 1c. Humans and their machines use almost all of their "speed potential" to move forward on the time dimension and only a very tiny fraction to move on the space dimension. But the faster you move on the space direction the less "speed" you have available for the time axis, so time goes slower, till you get a photon, where (almost) all your speed potential is used for the space axis, so time more or less stands still for you.

I'm not sure how far or near I'm to reality with this thoughts, but if it's not totally wrong it helps to understand it

 

[Wiccan_Child]

Even uniform acceleration can kill if applied too quickly though, surely? Impulse would be a big factor still.

It's the compression that kills you, your organs crashing into one another and your bones breaking under the tension. So yes, too much acceleration can kill you, regardless of how it's distributed.

 

[Chesterton]

It's the compression that kills you, your organs crashing into one another and your bones breaking under the tension. So yes, too much acceleration can kill you, regardless of how it's distributed.

 

[Cabal]

It's the compression that kills you, your organs crashing into one another and your bones breaking under the tension. So yes, too much acceleration can kill you, regardless of how it's distributed.

Yes indeed, those are the effects of too high an impulse, I guess I was just generalising the initial concept you put forward - there's only so much our bodies can take, be it a limb or the whole.

 

[Cabal]

Haha, technically not, but "deceleration in a sufficiently short time span can result in major injuries to one or more areas of your body" wouldn't fit as well on a t-shirt.

 

[Chesterton]

Haha, technically not, but "deceleration in a sufficiently short time span can result in major injuries to one or more areas of your body" wouldn't fit as well on a t-shirt.

 

[gipsy]

It's not the fall that kills you — it's the sudden stop at the end.

 

[AV1611VET]

Yes indeed, those are the effects of too high an impulse, I guess I was just generalising the initial concept you put forward - there's only so much our bodies can take, be it a limb or the whole.

Science used to teach that anyone accelerating to 30 m.p.h. or higher would die.

 

[Chesterton]

Science used to teach that anyone accelerating to 30 m.p.h. or higher would die.

Well they will...eventually.

 

[AV1611VET]

Haha, technically not, but "deceleration in a sufficiently short time span can result in major injuries to one or more areas of your body" wouldn't fit as well on a t-shirt.

It's not the fall that kills you — it's the sudden stop at the end.

I have a feeling scientists know something they aren't telling us.

According to empirical observation, unidentified flying objects have accelerated to above-mach speeds from 0 instantaneously, and have even made 90-degree turns at above-mach speeds, with no noticeable damage.

In my opinion, such maneuvers would have killed the crew; but instead, some scientists evidently think these phenomena are valid enough to build an array of radiotelescopes to attempt communication.

 

[Wiccan_Child]

Science used to teach that anyone accelerating to 30 m.p.h. or higher would die.

If memory serves, it was that moving at 30mph in an open-air carriage would kill you, and it was a public misconception, not actual science.

But even if it was, science moves on. Our earlier mistakes paved the way for a greater understanding. That's why I have that quote at the top of my signature.

 

[Wiccan_Child]

I have a feeling scientists know something they aren't telling us.

According to empirical observation, unidentified flying objects have accelerated to above-mach speeds, and have even made 90-degree turns at above-mach speeds, with no noticeable damage.

In my opinion, such maneuvers would have killed the crew; but instead, some scientists evidently think these phenomena are valid enough to build an array of radiotelescopes to attempt communication.

It's not inconcievable that an advanced alien race would be able to do things that we cannot. Who, in the 17[sup]th[/sup] century, would know that modern day humans could go to the Moon, communicate instantly across the planet, store food for years at a time, annihilate entire cities with a bomb, etc.

 

[AV1611VET]

If memory serves, it was that moving at 30mph in an open-air carriage would kill you, and it was a public misconception, not actual science.

Oh, I see --- blame the public.

 

[Wiccan_Child]

Oh, I see --- blame the public.

Well, it was the public. Is it the fault of the scientific community that people in Korea (or is it Vietnam...) think that a room fan will suck the oxygen our of your lungs? Public misconceptions are just that: misconceptions by the public. They're unfortunate, but unavoidable.