Why we will never leave our Solar System

[Spearka]

we are all forgetting one thing, humans have their own gravity, even if it is negligible

[Ydoow]

a) Newtons are a unit of force, not pressure. What you instead want is a unit such as newtons/square meter

1 Newton is approximately the force exerted by gravity on an apple. If I have an apple sitting on my hand, it does not implode, so I have to assume if I have one newton pushing outwards it would not explode either.

Now for radiation.

As somebody else mentioned, there are two senses the word \'radiation\' is commonly used in scientifically. The first is as in 'Thermal Radiation'. All bodies emit radiation in the form of photons of light at all times. The amount of radiation emitted, and the wavelength of the photons, varies based on the temperature of the body. The stephan boltzman law of blackbody radiation gives:

P/A = sigma * T^4 for a black body. A black body is simply a perfect emitter of radiation. Most objects are not black bodies, and so there is an extra constant in front called Emmisivity represented by Epsilon. Emissivity varies between 0, for a perfect reflector, and 1, for a perfect black body radiator.

The wavelength of light emitted is a continuum, however it has a peak at lambda = b/T where b is the constant 2.9*10^-3K m (Kelvin Meters). This gives a peak wavelength of around 10 micrometers for a body radiating at room temperature. This is in the infrared and not in the visible spectrum (~0.4-0.8 micrometers is visible) which explains why you do not consantly see light emitting from everyday objects. However, if you heat something up, the wavelength will drop into the visible. This is where the expressions 'Red hot' 'White hot' 'Blue hot' come from. Each of these simply means the peak of the radiation is at that portion of the visible spectrum. White hot implies the peak is right in the middle of the visible, so you see all the visible wavelengths combined into white. Blue is even hotter, as now most of the radiation is at the very low wavelengths.

Now, you might ask, if all materials are constantly emitting radiation, why don\'t they simply shed all of their energy and cool down to absolute zero?

Good question. This is because everything else is also emitting radiation. For an environment in equilibrium, they are all emitting the same radiation. Each of the bodies then absorbs the radiation the others emit, keeping everything at a constant temperature. However, if there is a temperature differential between two radiating objects, there is a net energy transfer. To find the rate of energy transfer, you simply take the difference between the energy input, and the energy output.

Power/area in = epsilon * sigma * T_surroundings⁴

Power/area out = epsilon * sigma * T_object⁴

Net power/area = epsilon * sigma * (T_surroundings⁴ - T_object⁴)

The temperature quoted for space, 3K = -270C, is given by the radiation temperature of the cosmic microwave background. It\'s a microwave background because the wavelength is rather large, owing to the low temperature. Wavelengths are simply a form of electromagnetic radiation that has a low energy and hence a relatively long wavelength, 1mm-1m.

However, if you are currently being illuminated by a star, the local temperature will be much higher because the radiation from the star is clearly much more energetic then the microwave background. This is why keeping cool is often more of a problem then keeping warm; the energy in from the star is much more then the energy that you radiate out.

Having dealt with thermal radiation, let us move on to the other sense that the word is used. This is as in 'ionizing radiation'. This is the sort of radiation that can cause cancer. The term 'Ionizing' simply means that the radiation has enough energy to ionize an atom, which means to knock an electron off the atom. Electrons are bound to atoms by electric fields from the opposite charge of the electron and the positive nucleus of an atom. The binding energy varies between atoms, depending on which electron you are looking at, and how big the nucleus is. Electrons in higher shells (further out) tend to be more weakly bound then those closer in, as would be expected. However, a good average value for the binding energy of the outermost electron in atoms is -10eV. This means you require 10eV of energy to knock that electron out.

Now, 10eV (electron volts) of energy is not very much, that is 1.6*10^-18 Joules or 4.5 * 10^-25 kilowatt hours, to quote some units you may be familiar with. However, the important thing here comes from quantum mechanics. Electrons will only absorb energy in specific bits called quanta, and that quanta must be large enough on its own to knock the electron out. You cannot keep shooting less energy quanta of light (called photons) at the electron until you have given it enough energy to leave, they simply wont eb absorbed and the electron will carry on. You must fire a photon that has an energy greater then 10eV to knock that electron off. The energy of a photon of light is given by its wavelength through the relationship hc/lambda where h is plancks constant, 6.6 x 10^-34 m^2 kg/ s, c is the speed of light in a vacuum, 3 * 10^8 m/s, and lambda is the wavelength. This gives a wavelength of around 120nm to ionize atoms. This is called ultraviolet radiation, which is why it is recommended you do not use tanning beds, and wear sunscreen, as both the Sun and tanning beds emit UV radiation. Recall microwave radiation, suchin as used in cell phones, has a wavelength of above 1mm, and thus is far, far below the energy that can ionize atoms. However, it does heat water up as you see in a microwave, and since your brain is mostly water, shooting microwaves at it all day is likely not particularly great for it.

However, ultraviolet radiation only has enough energy to ionize a single atom, which isnt so bad. Higher energy forms of radiation, such as x-rays or gamma rays, can ionize many more atoms before their energy is used up, making them more dangerous. Fortunately, they also tend to be much rarer. While ultraviolet can be produced through black body radiation by objects at a few thousand degrees, it would take an object sitting at millions of degrees Kelvin to emit Xrays such as those seen in medical equipment. Fortunately, such objects are extremely rare, and backgrounds like these are not a problem. Practically, X-rays in diagonostic equipment are produced by another process. This is where an electron is accelerated very quickly at a target material. When the electron hits the target and slows down, the slowing down causes an emission of Bremstrahlung radiation, which simply means 'Braking radiation' in german. This radiation is high energy, and so is called X-rays. These are used as the higher energy radiation, the further it can penetrate through objects. Therefore, X-rays can penetrate through you, but less so through bones. This gives the contrast that you see on medical X-rays.

Gamma rays, some of the highest energy electromagnetic radiation, are produced by nuclear processes. They are emitted when the nuceleons (protons and neutrons) in the nucleus of an atom rearrange themselves following the emission of some other sort of radiation such as alpha or beta particles. This energy is very high energy because the energy differences inside the nucleus of the atom are very high. Therefore, gammas rays are very penetrating (can only be stopped by meters of lead), and have the potential to ionize many, many atoms.

The other two types of radiation I just mentioned, alpha and beta particles, are also emitted in nuclear processes. Alpha particles are a helium 4 nucleus, with 2 protons and 2 neutrons, emitted from an atom with an energy of around 5MeV (varies by decay). These particles are relatively large, and charges, so they interact readily with matter. This makes them easy to absorb, and they can be stopped by a thin absorber such as a thin sheet of plastic. Beta particles are electrons that are emitted in nuclear process with energies ranging from a few 100 keV to several MeV. They are intermediatly penetrating, to stop them you need a thick sheet of plastic or a thin sheet of aluminum.

The most important thing to realize about these sources of nuclear radiation is that they emit isotropically in all directions. That means that as you move away, the radiation intensity drops as 1/R^2. If you are 10m away, you get 100x less radiation then if you are 1m away. So, moral of the story, the best protection is distance.

The concern about ionizing radiation in generl is DNA mutation, and interference with other cellular process. If you knock an electron off of an atom in a DNA molecule, you will disrupt the bond, possibly causing one of the DNA bases to be removed, introducing a mutation. Other process can also be interfered with when certain key bonds are broken down, which is why in general ionization radiation is not a good thing.

Anyways, I hope that none of you read this, as you probably will have gotten bored, fallen asleep at your desk, and then gotten brain damage as your head fell to impact your desk, and I would not want that on my conscience.

Cheers.

I actually read that entire thing and found it extremely interesting.

I\'ve already been taught it several times (of course, with time I forget chunks of it...), and it was great to re-learn it all because it came back to fill in new things I\'ve learned.

I forgot if Wavelength or Frequency increased eV to knock electrons off atoms.

You said Wavelength, specifically UV wavelength which perfectly ties into what I\'ve learned in chemistry.

Having conjugated pi-bonds in a molecule (like carotene) allows electrons to have 'options' on which atom it can go to, chemists call it resonance.

Having greater resonance creates greater stability for the molecule. It becomes less rigid and more flexible so to speak. Think of a building swaying with the wind vs. snapping because it\'s so rigid.

Having large amounts of conjugated pi bonds allow the electrons to be excited by lower Wavelength photons, dipping into Visible Spectra.

Carotene sounds like Carrot for a reason. That molecule begins to absorb violet spectra, making it appear orange-red.

This is (at least it used to be) the main method for creating cloth dyes.

I have a question on keeping warm/cool in space.

The sun emits a lot more Thermal Radiation than background radiation, clearly.

But don\'t we absorb/emit radiation at the same constant, so wouldn\'t we be fine with maintaining a balance?

I understand that there must be a change in temperature when you drop behind, and pop out from the earth (blocking/revealing the sun).

This is assuming we\'re in a space craft in Orbit, by the way.

[rdfox]

I apologize for the necro (sorry, but when I got 0.14 and it crashed every time I tried to start it, I lost interest for a while), but apparently, we *have* left the Sol system now, at least in the form of an unmanned probe--Voyager 1 apparently crossed the heliopause in the last month, meaning it is now officially beyond the boundaries of the system. (Pioneer 10 and 11 may have also crossed it; I can\'t remember if they\'re the furthest out now, or Voy1, but still.)

Not to mention that the three probes above, plus Voyager 2 and Pluto New Horizons, were all accelerated to above solar escape velocity on trajectories that wouldn\'t result in a gravity-assist reinsertion into solar orbit, and thus technically left solar orbit when they injected onto their final Earth departure trajectories. Saying that they\'d never leave the solar system because they\'ll always be under some influence from Sol\'s gravity is like saying that Earth is part of the Gliese 581 system, because Gliese 581\'s gravity has some influence on Earth\'s velocity--it makes much more sense to say that something is part of a star system if it is either the central star (or one of the central stars, for polystellar systems where the barycenter of the stars is not below one star\'s surface), or captured into orbit around the star...

[ping111]

I apologize for the necro (sorry, but when I got 0.14 and it crashed every time I tried to start it, I lost interest for a while), but apparently, we *have* left the Sol system now, at least in the form of an unmanned probe--Voyager 1 apparently crossed the heliopause in the last month, meaning it is now officially beyond the boundaries of the system. (Pioneer 10 and 11 may have also crossed it; I can\'t remember if they\'re the furthest out now, or Voy1, but still.)

Not to mention that the three probes above, plus Voyager 2 and Pluto New Horizons, were all accelerated to above solar escape velocity on trajectories that wouldn\'t result in a gravity-assist reinsertion into solar orbit, and thus technically left solar orbit when they injected onto their final Earth departure trajectories. Saying that they\'d never leave the solar system because they\'ll always be under some influence from Sol\'s gravity is like saying that Earth is part of the Gliese 581 system, because Gliese 581\'s gravity has some influence on Earth\'s velocity--it makes much more sense to say that something is part of a star system if it is either the central star (or one of the central stars, for polystellar systems where the barycenter of the stars is not below one star\'s surface), or captured into orbit around the star...

That wasn\'t the original issue. I believed that if we didn\'t have any gravity to compress our insides to stay, well, inside us, they would expand in all directions like a bubble in a vacuum. I now see the light that I was getting these two subjects, of gravity and pressure, confused.

[Ydoow]

That wasn\'t the original issue. I believed that if we didn\'t have any gravity to compress our insides to stay, well, inside us, they would expand in all directions like a bubble in a vacuum. I now see the light that I was getting these two subjects, of gravity and pressure, confused.

Learning is fun!

[Aerzee]

It was an interesting read through...

[Twinky827]

Ahem, FAKE GRAVITY GENERATORS. And, who knows what humans will come up with? Someday, we may be almost invincible (Unfourtunatly)

[OtherDalfite]

Ahem, FAKE GRAVITY GENERATORS. And, who knows what humans will come up with? Someday, we may be almost invincible (Unfourtunatly)

Sure, gravity generators, we\'ll just build those when we feel like it. Do you even consider having to research, design, and build these technologies?

[Ted]

Sure, gravity generators, we\'ll just build those when we feel like it. Do you even consider having to research, design, and build these technologies?

Using the inertia of objects in circular motion it is possible to create a gravity-like force. As for further R&D, testing and building, that would be troublesome, but not impossible.

Also, this thread caused me physical pain to read..

[ping111]

Using the inertia of objects in circular motion it is possible to create a gravity-like force. As for further R&D, testing and building, that would be troublesome, but not impossible.

Also, this thread caused me physical pain to read..

I\'m sorry! :\'( Just read my birthdate on my profile...

[Ted]

I\'m sorry! :\'( Just read my birthdate on my profile...

Ahem, isn\'t the minimum age on forums 13..?

[ping111]

Ahem, isn\'t the minimum age on forums 13..?

GOWAI.

[Ted]

GOWAI.

And there\'s proof as to why the age limit is there..

[ping111]

And there\'s proof as to why the age limit is there..

Oh, come on. If you read some of my earlier posts, you can see how mature I am.

[Ted]

Oh, come on. If you read some of my earlier posts, you can see how mature I am.

Haha yeah, I didn\'t suspect your age might be below about 15-16 until this thread.

Anyway, we\'re veering incredibly off topic. It\'s good that you now know the difference between the effects of gravity and the effects of pressure on humans.

[Radion]

Despite the headache I got from reading this thread, I\'m glad you\'ve come to the realization of facts.

[Ydoow]

Hey, just be glad you got to see the aftermath.

I was here at the start of this thread, and just having the fear that this thread may never had a good conclusion made me slightly suicidal.

[HOC]

It seems that many people have ended this thread with a headache :/

It\'s practically nerd-baiting now, people see the title and go 'NO WAY' and click to read on... then they see the original post and go 'THAT MUST BE WRONG' and read on...

Ouch, my head.

[ping111]

It seems that many people have ended this thread with a headache :/

It\'s practically nerd-baiting now, people see the title and go 'NO WAY' and click to read on... then they see the original post and go 'THAT MUST BE WRONG' and read on...

Ouch, my head.

I\'m sorry! Should I just lock it....? I don\'t really want to; it\'s a live-and-learn experience, and teach people to at least read some comments before doing anything.

[Ydoow]

Hm. I don\'t exactly believe in locking threads purely because they\'re necroed, but I fear there\'s going to be one person who\'s all *reads first post* 'THIS GUY IS AN IDIOT'

*Types huge rant before reading the rest of thread*

and then this giant troll fight will break out and...yeah...

[LockeCole]

It was an interesting read through...

Pardon but, I believe your troll may need to see a head trauma specialist in the near future. Unfortunately, unless you find one in a dream bubble in the relatively near future you may be too late to repair any damage impact trauma and/or accidental ingestion of sopor slime may have caused.

On the topic of the thread, I am very glad to see KSP has players willing to explain, iterate and reiterate the physics of vacuums, pressurized vessels and gravity. I wish there were easier, more understandable ways to explain these things to our younger members, but I do see the point got across.

Thank you for educating me, I knew the original post couldn\'t be correct, but I did learn some interesting tid bits I did not know prior to this thread.

[mincespy]

About artificial gravity generators, we already have those.

[Johno]

Ping: Don\'t worry about it. You\'re faced with a basic problem - nobody can see your face, so we tend to assume that any misconceptions you speak are because you\'re ignorant or foolish. Most people don\'t consider the possibility that you might just be young.

This isn\'t a problem for me, however. I\'m a teacher. Dealing with the misconceptions of kids is what I do! (And yours are far from the silliest misconceptions I\'ve had to correct . . .)

Anyone who wants to have a go at Ping: LAY OFF THE KID.

[rdfox]

Ping: Sorry, I didn\'t actually read the whole thread (when you\'ve got about three or four months worth of threads to catch up on, you\'ll often just scan the first page!), so I misunderstood your reasoning. And clearly, I missed where people did explain the situation to you. So I apologize for my post!

[ping111]

No probs everyone! If I make a mistake, it\'s OK for you to make one too by calling me out on it before finishing up the thread!