Free fall questions

[orionrider]

I have a few questions about 'free fall' and the history of time:

Suppose you are inside a small windowless spacecraft floating freely in outer space, all external sensors disabled. Then your vessel gets attracted by the mass of a very large body. The craft accelerates in the general direction of the massive object.

1. Would you be aware of this acceleration :?:
I assume that you wouldn't feel a thing because gravity has the same effect on you as on the spacecraft?

If the answer is 'no', let's accelerate some more...

2. The massive body being really massive, you spiral down to a significant fraction of c. I read somewhere that you and the spacecraft would shrink, that time would slow, mass increase and other niceties. But would you as a passenger be aware of that :?:
Nausea, Headache, glow-in-the-dark, changed to primordial soup...

If the answer is still 'no', let's accelerate even more...

3. Damned, the massive body was in fact a supergiant black hole!
This time the brown matter hits the fan, you dangerously approach the horizon, close to the speed of light. Apart for the massive dose of radiation, how do you feel :?:
I assume that whatever the gravity, you are still basically free falling. Time/space itself gets stretched, which means you nicely stay under c-speed, yet keep accelerating, but that is probably relative :?

Now enter the speculative mode:

4. That's it, we can't see you anymore, you're somewhere in the dust bag of the giant Hoover. Are you still there or has Higgs ripped you into quantum subparticles and Hawking light?
What about tidal forces and Spaghettification? Obviously, your craft is so small it wouldn't be subjected to angular stresses until very close to the singularity. Besides, if you 'fly' very close to c-speed, how can some part of the vessel go faster than another :?:

Sorry for the long post, but this is really confusing :mrgreen:

 

[origin]

I have a few questions about 'free fall' and the history of time:

Suppose you are inside a small windowless spacecraft floating freely in outer space, all external sensors disabled. Then your vessel gets attracted by the mass of a very large body. The craft accelerates in the general direction of the massive object.

1. Would you be aware of this acceleration :?:
I assume that you wouldn't feel a thing because gravity has the same effect on you as on the spacecraft?

Nope, you would not 'feel' anything that told you that you were accelerating.

If the answer is 'no', let's accelerate some more...

2. The massive body being really massive, you spiral down to a significant fraction of c. I read somewhere that you and the spacecraft would shrink, that time would slow, mass increase and other niceties. But would you as a passenger be aware of that :?:
Nausea, Headache, glow-in-the-dark, changed to primordial soup...

Nope still nothing you would feel just swell.

If the answer is still 'no', let's accelerate even more...

3. Damned, the massive body was in fact a supergiant black hole!
This time the brown matter hits the fan, you dangerously approach the horizon, close to the speed of light. Apart for the massive dose of radiation, how do you feel :?:
I assume that whatever the gravity, you are still basically free falling. Time/space itself gets stretched, which means you nicely stay under c-speed, yet keep accelerating, but that is probably relative :?

It is interesting that you used a supermassive black hole because in that case if the black hole is large enough you would pass through the event horizon and not feel anything. Now for a stellar sized black hole as you neared the event horizon the difference in gravity between your head and your feet would literally tear you apart which you would most definately notice!

Now enter the speculative mode:

4. That's it, we can't see you anymore, you're somewhere in the dust bag of the giant Hoover. Are you still there or has Higgs ripped you into quantum subparticles and Hawking light?
What about tidal forces and Spaghettification? Obviously, your craft is so small it wouldn't be subjected to angular stresses until very close to the singularity. Besides, if you 'fly' very close to c-speed, how can some part of the vessel go faster than another :?:

Sorry for the long post, but this is really confusing :mrgreen:

Like I said if the black hole is massive enough there will not be large tidal affects. In any case you are still in a heap of trouble.

 

[a_lost_packet_]

I have a few questions about 'free fall' and the history of time:

Suppose you are inside a small windowless spacecraft floating freely in outer space, all external sensors disabled. Then your vessel gets attracted by the mass of a very large body. The craft accelerates in the general direction of the massive object.

1. Would you be aware of this acceleration :?:
I assume that you wouldn't feel a thing because gravity has the same effect on you as on the spacecraft?

Eventually, you would feel the acceleration. One way or another... If nothing else, you would begin to feel it as "gravity" which is impossible to differentiate from acceleration. (The rate of acceleration is important, I imagine.)

2. The massive body being really massive, you spiral down to a significant fraction of c. I read somewhere that you and the spacecraft would shrink, that time would slow, mass increase and other niceties. But would you as a passenger be aware of that :?: Nausea, Headache, glow-in-the-dark, changed to primordial soup...

It is more accurate that you would contract, not shrink. You would contract in the direction of acceleration. No, you would not be aware of it.

3. Damned, the massive body was in fact a supergiant black hole!
This time the brown matter hits the fan, you dangerously approach the horizon, close to the speed of light. Apart for the massive dose of radiation, how do you feel :?: I assume that whatever the gravity, you are still basically free falling. Time/space itself gets stretched, which means you nicely stay under c-speed, yet keep accelerating, but that is probably relative :?

Assuming there is some mechanism to get you close to the speed of light you'd still be fine. But, that's a lot of acceleration due to a nearby mass.. what provides the gravity to achieve it over that distance without collapsing in on itself?

Now enter the speculative mode:

4. That's it, we can't see you anymore, you're somewhere in the dust bag of the giant Hoover. Are you still there or has Higgs ripped you into quantum subparticles and Hawking light? What about tidal forces and Spaghettification? Obviously, your craft is so small it wouldn't be subjected to angular stresses until very close to the singularity.

Immediately past the Event Horizon you wouldn't notice anything different even though you were doomed to never leave... As you approached the singularity, different parts of you would accelerate at different rates. Not only would you be drawn out but, you'd be spread out as well. In fact, instead of spaghetti you'd start to resemble a pancake.

Besides, if you 'fly' very close to c-speed, how can some part of the vessel go faster than another :?

I'm not sure what you mean by "fly." So far, we're talking about a uniform acceleration. If you're talking about being close to a steep gravity well then part of the ship is really "falling faster" than other parts because of curved space. Think of it as having one part hanging over a a steep edge with the rest tracking behind, like a roller coaster. Except, this hill takes an extraordinary long time, depending upon your perspective, to bottom out...

Sorry for the long post, but this is really confusing :mrgreen:

That's fine. I'm only answering to see how my answers hold up in court... Here, where people will honestly correct you when and provide references when you goof up.

(Net connection just blew out.. again.. /sigh So, I'll post this when it comes back but, leave my answers unchanged. None have responded to the thread as of the time I wrote the above. 8am or thereabouts.)

 

[theridane]

Actually (re: 1) you would be able to feel the acceleration, via tidal forces. Your space capsule would most likely be larger than you (duh), and therefore a part of it would be closer to the planet/black hole/swarm of puppies/whatever. It would therefore accelerate a tiny bit faster than you, and you'll bump your head. Or you could use a bunch of ultra-precise accelerometers mounted firmly in different places around the craft - those closer to the mass will measure higher acceleration (this is how GOCE, the most bad-ass thing in LEO, works).

Edit: And as you'd be getting closer to the supermassive black hole (also made of puppies), those tidal forces would slowly start being an issue (check Neil deGrasse Tyson telling the account of a person falling down a black hole).

 

[origin]

I have a few questions about 'free fall' and the history of time:

Suppose you are inside a small windowless spacecraft floating freely in outer space, all external sensors disabled. Then your vessel gets attracted by the mass of a very large body. The craft accelerates in the general direction of the massive object.

1. Would you be aware of this acceleration :?:
I assume that you wouldn't feel a thing because gravity has the same effect on you as on the spacecraft?

Eventually, you would feel the acceleration. One way or another... If nothing else, you would begin to feel it as "gravity" which is impossible to differentiate from acceleration. (The rate of acceleration is important, I imagine.)

Why would you feel the acceleration? Astronauts do not feel acceleration as the fall towards earth while in orbit. If you were a hundred thousand km from earth in a large box and stationary relative to earth you would feel some gravity as you stood on the floor of the box you were in. If the box was released it would begin to fall to earth. Both you, the box and the air in the box would all be accelerating at the same rate. I do not think there would be any sensation of acceleration no matter how high the gravity. We feel acceleration in a car or plane for instance because the seat back pushes us forward and so there is pressure on our backs and even our organs are pushed from the inside against our backs. In the case of free fall the acceleration is due to gravity which is affecting out entire body so there is no differential pressures to cue us that we are accelerating.

 

[orionrider]

Thanks for the links and sometimes conflicting answers

(1) gravity would equally apply to the craft and everything inside, be it a feather or a hammer, so I'm quite certain the astronauts would not feel the acceleration until tidal forces become significant.

(2) has been tested in molecular accelerators, and it looks like molecules don't fall apart when approaching c, which is good news for our crew. So there seems to be a consensus on that one.

(3) http://www.space.com/scienceastronomy/0 ... -hole.html

(4) actually I found a partial answer on Wikipedia. But it says nothing of the interactions of an object accelerated to relativistic speeds falling into the horizon. It shrinks due to Einstein's speed limit, but gets elongated by Hawking pulling the feet :?

And what about the kinetic energy of the mass falling at 99% c? Is it what causes the jets of the supermassive BH, when the falling object reaches the singularity and stops dead (so to speak) :?:

 

[theridane]

There's no such thing as insignificant tidal forces

Imagine a capsule in a circular LEO around a perfectly homogenous, spherical, airless Earth. Its center of gravity is exactly 200 km ASL. Now suppose there's a small object inside, positioned exactly 1 meter away from capsule's cg, at 200001 m ASL, floating perfectly still. There will be a small tidal acceleration acting upon it, approx. 2.8 μm/s². Looks puny, but it's enough to move that object almost 2 ft away within 10 minutes, something an astronaut (bored to death from floating for ages in a windowless capsule) would definitely notice.

 

[orionrider]

Thank you theridane, I don't have the math or the knowledge to calculate that, I'm impressed!

But 200 km is a tiny distance, astronomically speaking. Especially if you travel at 99% c.
I was not speaking of your average BH. Mine is bigger: the 3 x 10^9 km supermassive galactic-core, jet-spewing BH!
The unsuspecting crew would actually have a few seconds inside the horizon before the cracking noises give away their destiny :lol:

 

[emperor_of_localgroup]

'theridance' may be right in this case.

Mass of spacecraft is definitely mush higher than passenger's (assuming an average human) mass. Assuming the craft was travelling at constant velocity before it entered in to the gravitational field, the spacecraft will be pulled by a larger force than the passenger. But the acceleration of both spacecraft and passenger are the same

a = GM/R^2.

a= acceleration, G= gravity constant, M=mass of attracting object, R=distance. It all depends on R.
Theoretically speaking, if center of mass of the craft and center of mass of passenger are the same, passenger would not feel the acceleration. But it would be very difficult to make these 2 points coincide, which will create a 'very minute' difference in acceleration.

Correct me, if my interpretation is wrong. I'm not a genius.

 

[a_lost_packet_]

...Why would you feel the acceleration? Astronauts do not feel acceleration as the fall towards earth while in orbit. If you were a hundred thousand km from earth in a large box and stationary relative to earth you would feel some gravity as you stood on the floor of the box you were in. If the box was released it would begin to fall to earth. Both you, the box and the air in the box would all be accelerating at the same rate. I do not think there would be any sensation of acceleration no matter how high the gravity. We feel acceleration in a car or plane for instance because the seat back pushes us forward and so there is pressure on our backs and even our organs are pushed from the inside against our backs. In the case of free fall the acceleration is due to gravity which is affecting out entire body so there is no differential pressures to cue us that we are accelerating.

You'd feel the acceleration because Einstein say's so.

If it was a constant velocity, that's something entirely different. But, under a constant acceleration you would feel it. In fact, you are constantly accelerating towards the Earth, right now, at 1g acceleration. That's what keeps you on the planet. You keep from sliding through to the center because, despite how strong gravity is, the nuclear forces holding your body's constituents together, and those of the ground, are stronger.

In General Relativity Einstein stated it is impossible to tell the difference between the effects of gravity versus the effects of acceleration without an external reference frame. And, since there isn't a platonic, absolute frame of reference in the Universe.. well, there ya go. Gravity and acceleration are equivalent.

That's my take on it, at least.

 

[SpaceTas]

Separate the 2 situations: free fall, and powered acceleration.


In free fall you are accelerating at the local rate of acceleration of gravity; and so feel weightless. It shouldn't matter what the acceleration is or what speed you travel at. You may notice changes in acceleration as a jerk. Otherwise a smooth ride.
This is the non-relativistic view.

In powered acceleration (without gravity), you feel the acceleration e.g. being pushed into your seat as a car accelerates, as a force. The basic principle o general relativity is the equivalence of acceleration and gravity. You can't tell the difference, so the laws of motion work inside your spaceship (local reference frame) as if either gravity or acceleration is taking place. So when your spaceship is accelerating at 1 g (9.8m/s/s) you feel as tough you are on the Earth (1 g of gravitational force). Any test you do (bounce a ball, fire a laser light ..) you could not tell the difference. This principle should hold no matter what your acceleration. Of course most people black out well before 6 G's, your bones would break and you'd be jelly at a high enough powered acceleration.

But free fall is zero net acceleration within your spaceship (local reference) and so zero net weight.

Some basic physics: enjoy
In the case of powered acceleration plus gravity, just add the 2 acceleration or Forces as vectors taking into account that the force you feel is actually that of the floor (seat) pushing on you (Fnormal)

Equation: Fgravity + Fnormal = massXacceleration (acceleration of local frame)
Equation: Acceleration(gravity) + Acceleration(normal) = acceleration(you and spaceship)

free fall: acceleration (gravity) is 1g down, acceleration(ship) is 1g down: Take down as negative direction
-1g + Accelaration(normal) = -1g
Acceleration (normal) = 0g

Ship puts on engines and accelerates up at 1g
-1g + Acceleration(normal) = +1g
Acceleration(normal) = 2g

So ship's pushes you up at 2g's so you feel twice you normal weight
Have a play: figure out what happens when the ship accelerates downward at 2g. Hint "Walking on the ceiling"

 

[orionrider]

We feel the gravity on Earth because the ground is resisting the acceleration. No resistance, no weight, no feeling.

SpaceTas: believe me I know about so-called 'negative' G: objects falling to the ceiling and the difficulty to use a barf bag... :shock: :mrgreen:

 

[SpeedFreek]

You'd feel the acceleration because Einstein say's so.

Not if you were free-falling, you wouldn't.

 

[a_lost_packet_]

Separate the 2 situations: free fall, and powered acceleration.

So, I should have paid a bit more attention to "free fall" instead of focusing on acceleration.

In free fall you are accelerating at the local rate of acceleration of gravity; and so feel weightless. It shouldn't matter what the acceleration is or what speed you travel at. You may notice changes in acceleration as a jerk. Otherwise a smooth ride.This is the non-relativistic view.

So, this would apply even under constant acceleration as long as that acceleration was due to gravity?

I understand. Admittedly, it's what I thought at first but, I started thinking a bit too much about acceleration=gravity.

 

[a_lost_packet_]

You'd feel the acceleration because Einstein say's so.

Not if you were free-falling, you wouldn't.

Understood. I didn't pay enough attention to "free fall."

 

[neilsox]

So you are falling straight toward the super massive singularity, at 1/2 c. Nothing special happens when you penetrate the event horizon. You are 3 million kilometers from the singularity = less than 20 second to impact if you accelerate some more. Because of your high speed and the strong gravity, your craft is hitting 20 sub atomic particles per second = your speed is less than free fall, due to "air" friction so you may be experiencing about one g of gravity. Gravity will crush you into a bulkhead in perhaps 5 more seconds, then your corpse will be torn apart by tide. The radiation is deadly from 20 subatomic particle hitting at perhaps 0.8 c, average, but you already have fatal injuries due to the tide = gravity difference from head to toe, and being crushed by the bulk head. Your craft is disintegrating, and your air escaping rapidly. Good by.
More likely your craft was hitting 100 subatomic particles per second when you were ten million kilometers from the singularity and only going 0.4 c, so you were already crushed by the bulk head due to going slower than free fall, and had already received a fatal dose of radiation due to the subatomic particles hitting your ship. Neil

 

[orionrider]

your craft is hitting 20 sub atomic particles per second

I'm not sure of that. Since the craft is in free fall, everything in the vicinity of the craft would be accelerating at the same rate towards the BH. Everything in front of the spacecraft would be closer to the BH and accelerating faster. And everything behind the craft would be slower. Only massless photons would hit the craft, delivering high doses of radiation.

 

[neilsox]

I agree, fewer particle hits per second, if you are optimally spiraling in toward the black hole with the accretion disk. Yes you are moving 1/2 c or faster, but almost at right angles to the direction to the black hole. It may take days to cross the event horizon. The original post seems to suggest that you are heading directly toward the singularity. Your craft may be designed to reduce crew exposure to radiation, but the system will likely be overwhelmed moving close to right angles to the particles moving in a typical accretion disk.
On second thought, there are likely as many sub atomic particles within ten million kilometers of a super massive black hole in all directions as in our inner solar system, and traveling much faster on the average. This is because particles do escape from inside the event horizon, but fall back into the event horizon = slower than escape velocity = they lost most of their speed by the time the left the event horizon and very energetic collisions are occurring in the accretion disk and polar jets, which scatter sub atomic particles. Please correct my errors. Neil