240 posts • joined 14 Nov 2007
Idealism vs pragmatism
Kind of weird that in the last episode the right choice was the ignore the wish of an entire planet and put them all at great risk on the long shot that some unknown giant space birdie wouldn't go full blown toddler on the nearest gravitational well. All because the right choice on TV is always "doing the right thing", like in the moral dilemmas "Could you kill one guy if it was the only way to save a planet." and if you just say no then it will magically work out anyway.* While in this episode the conclusion is: "Sometimes the choices you have are bad ones, and you still have to choose."
It would have made a little sense if at least this was an argument between Clara and the Doctor, but it isn't, he endorsed her choice on the moon. And anyway, I do not think any characters opinion of reality should affect said reality, but in this world it clearly does. Stick to idealism: It works out. Stick to pragmatism: It works out.
Overall a watchable episode though. I just wish the new doctor had some consistency in this new dark persona of his.
*I am so glad TV-writers are not doctors doing triage.
Re: looks like no more Who for me... @SuccessCase
"I nearly got it wrong." she said, NO, you did get it wrong! It was a no brainer. All the humans (on the important continents facing the moon) voted kill it*, and it was the right choice. And I was sighing a relief, will this new version of doctor Who come with a once in a while making the right choice in moral dilemmas. Making the right choice are in very limited supply in the TV and movie world, and it frustrates me deeply. "Stop dragging it out and make the call! It is not a choice because there is only one option!", I scream to my TV**. And then the characters demonstrate to my disbelief that there is a choice after all, and to my surprise (not really anymore) the story that unfolds afterwards is not a story to hammer into us that stupendously bad choice the character made had dire consequences and the moral is don't be stupid. No, it hammers into us that we when presented with these "dilemmas" we should make the "bold" (not bold at all, but rather cowardly) choice, put millions or billions*** at other lives at risk and it will all work out.
Back to my sigh of relief when the lights went out on Earth and I thought I finally would have at least once somebody make the right choice. Then she pushes abort. And there is no chaos and destruction, and there is no being yelled at by this new doctor that is a breath of fresh air of not caring. No, there are bunnies and unicorns, but the doctor gets yelled at a bit.
So, yes, SuccessCase, I do not get it either, but people seem to like this. And I would like to understand why. Does anybody here think it was the right choice she made? Care to explain?
*Well, they turned it off in massive grids, so it might have been a government decision.
**In my head at least.
***And in this instance actually against their will. Why did you ask them Clara? You sure are a rotten person, despicable.
Iron Man, is that you? I didn't recognize you with that mask.
Re: The region lies at the top of the comet
You find the bottom and work your way upwards.
Come on guys, if we pull together we can make even more lame suggestions, I am sure.
Collision vs other explaination
I have trouble with the theory that it is made up of two bodies that fused together after a collision. While I see that it is possible, after all with such low gravity the two bodies could have collided with a speed as low as their combined escape velocity that isn't more than walking pace, and a slow one at that. Possible doesn't equal to likely in my humble opinion though. Wouldn't it be far more likely with the somewhat random orbits these things have that any rocks that collided would hit at far greater speeds?
Anybody enlightened out there that could tell me what I am missing?
Oh, and well done ESA for letting Rosetta take part in popular culture and take picture for her snapgram media.
Re: Tricky landing
It isn't, it would rip itself apart if it was. The rotation period is about 13 hours.
Tonight at eleven
When we do build it, this will be the news that day (prior to turning it on):
Also, would this be a Hrung?
Re: Climate change
I did read it, and I still do not see it as clear cut.* The problem with irony is that it is supposed to clear that you usually means the opposite of what you say. This is usually achieved by ensuring that what you are literally saying is beyond what any reasonable person could mean, and also that the recipients know that the sender is a reasonable person.
I have met quite a few people on the Internet, even here, and also a few face to face that could state exactly what "the Axe" said and mean it. (even without my assumption that the last sentence was just poorly drafted)
Anyhow, I'll let my original post stand to make people at ease and the next time they read some wacko's ramblings** they can just say "meh, it is just irony and I won't be fooled like the mr.K fella"
*I blame it partly on my slight fever and that I am not a native English speaker.¤
¤This is just an excuse.
Re: Climate change
Disclaimer: I am assuming that you are not sarcastic or something, and that you didn't mean you need to adjust the data [...] to match your models, but rather the other way around.
I would argue that there are loads of "proper science" that gather data on a phenomena before they venture out in creating theories and models which they then set up experiments to verify or rule out. Actually I would say that is the normal way to do it. After a "that is odd"-moment spending lots of time setting up theories and models when all you have is a single point of observation is a waste of time and can also be counterproductive. Take Darwin and his trips. Not calling his observation, cataloging and note taking in the field, prior to him forming his theory of evolution, for science makes the term a tad narrow for my use of it at least.
Pirate because Darwin probably had to watch out for those.
I am sorry, but mocking religious beliefs in commentard section of an article about astronomy is as cheap as it gets. If somebody had dragged their religion into it in the first place, maybe, but nobody did except you.
"A small step for man, a giant leap for mankind." is a cool including statement. He could have said some religious thing, he didn't. He could have made in American only, he didn't. It made us in the rest of the world able to say "We have been too the moon." and brought the world a little closer together.
"I see no god." is belittling and served as nothing else as to make me think less of mankind.
Re: Thunderbolts Project and the Electric Universe....
I do not think arguments will have any effect here. So...hug?
Re: Nazijonas Snickersmymidget (NSM)
Nasjonal is basically national with a proper spelling, and since we don't split our words into bits and pieces sikkerhetsmyndighet is put together of sikkerhet, which is not far off from security, and myndighet. It is from German mundich and...why do I bother, you lot couldn't even pronounce Eyjafjallajökull when the volcano erupted underneath it.
Re: Sounds fascinating...
Connecting this subject to quantum mechanics would be a leap.
Alright, alright, I am going.
Re: The first problem....
But isn't all physical currencies also pretty much untraceable? Actually one of the reasons we still have it around. Digital currencies do make it is easier to scale the amounts up though, I see that, still...
That is all. Just, well done!
Note: I am not sure if the mouse over text on the icon is the right message here, but I like it.
Re: Why do they never tell you why?
Science mostly. I am kind of tired to have to defend the value of science, but it is such an important issue that I will have to keep doing it. Science that leads directly to a product or benefit is paid for by itself by people buying these products afterwards. However all of todays technology and scientific breakthroughs are a result of science that had no purpose other than the science in itself, and it is too expensive for any company to embark on so we agreed on that we all chip in. Science is about understanding the universe and it's laws. When we constantly expand on that knowledge we pave way for other people to research the final details and make a use of it.
Claiming that all research has to end up with a result we can immediate use is like being a farmer in the stone age refusing to explore beyond the hills around his valley. Because from where he stands it is clear that hills can't be used to grow his crops and thus anything beyond can not possibly be of any use to him.
I would like it is purely due to science, but it is not. It is also about entertainment of sorts. While some people enjoy sport (which is heavily subsidized), I enjoy pictures taken close up from a big rock we discovered in 1969.
Re: What is the orbital period of 67P, and can Rosetta's batteries recharge from zero?
My bad, that is what I meant, just the wrong wørds.
Re: What is the orbital period of 67P, and can Rosetta's batteries recharge from zero?
The orbital period is quite easily googled and is currently six and a half year. I say currently as this is a comet and their orbits are frequently altered by planets they come to close to, with the gas giants being the usual suspects with their large mass and thus large area of influence. This one had it's orbit changed in 1959 by Jupiter, ten years before it was discovered.
As for if the batteries can be recharged from zero. I have no idea on the battery technology, but lots of batteries break if they are depleted. Which is a problem, you have to leave them with enough charge so any depletion done while left idle won't bring them under a certain threshold. I have not managed to find out if this is a problem with Rosetta, but my guess is that temperature is a bigger problem. Keeping key parts warm while out there in the cold for an extended period can be a problem that they have not seen the benefit in engineering around. Cold is what killed Spirit on Mars in the end.
I recommend NASA Eyes if you want a visual of the orbits:
Note: The probes we send out decades ago that is heading out of the solar system is driven by thermonuclear power sources and are kept warm that way.
Slightly speculative indeed
Is it even possible for it to burn out completely? ISON passed, or rather it tried, the sun's surface about twice the radius of the sun itself, and even then we had hopes that it could survive. 67p/Spiff-Zogwarg will be at 1.3 AU at its closest. That is one hundred times further out, which if my basic knowledge of astrophysics is correct, means around one ten thousandth of the radiation.
Regardless, I am quite exited over this. They are going to harpoon a comet. Apart from the Apollo 12 rum incident, how often are harpoons launched in space?
Re: I love napkin math!
When you turn on your flashlight the batteries releases chemically stored energy. It is believed* that also release of chemical energy results in a loss of mass, but that the amount of mass is so small that we are not able to measure it. I am not sure, but I do not believe that how the energy leaves the flash light matters. Be it via light or thermal conduction to it's surroundings.
*or so I have read on the Internet. Consult Stephen Fry if you are to use this information as anything other than trivia.
semantic topics within this corpus
First, I can not take anybody serious that writes sentences like this: “First, we take a large online corpus, Wikipedia, and use a well-known technique from computational linguistics to identify lists of words constituting semantic topics within this corpus,”
Second, this is yet another one of these prediction methods that are based upon on the assumption that history repeats itself. It doesn't. Yes, there are a few somewhat repeating patterns out there, quite a few in fact. But this is a system with a memory and the last outcome will carry with and ensure that you never have the same set of conditions required for the same outcome.
Third, the funny thing about economics is that it is a man made system, but not a fixed system. The rules change constantly, but also the knowledge of the participants (us) which influence how they behave. This leads to the fact that any new method to describe the system will change the system*. Thus if this method actually worked with any certainty then it would seize to do so as soon as people started to believe it can.
*It is required that the description is known to at least one that will change his behaviour due to it. It is not required that description or method actually has any validity whatsoever.
Re: Celsius? @cosymart
Would you look at that, I actually didn't know that. Any chance that you native English speakers could switch them around? It would comply with how we write it in Norwegian and I wouldn't have to adapt.
Never contemplated the difference before I have now read a little about and I am not making it fit with what you are saying. It seems that they are just two different names for the same scale. Where centigrade is the old one, centigrade, defined by water freezing and boiling and the new one is defined by that, but has moved the reference point to absolute zero in addition. It is however the same scale, just a new better definition technically giving a small difference. But that can also be said for all other units of measurements that change definition from time to time. The meter is still a meter even though we are not considering a platina staff or the distance between the poles and equator the definition anymore.
Further more as of any measurement you can never make them absolute accurate. Thus the unit is never tied up to the tool you are measuring with. I do not need to time light to measure the meter and I do not a constant volume gas thermometer to measure degrees Celsius. I can use any thermometer.
What am I missing?
While some people clearly have a too low threshold for calling emergency numbers*, that is not something that holds for everybody. The last thing they want is for people to contemplate over if their issue is serious enough to call for help. Instead they inform the public on occasion or with repeat offenders they have a talk. I think they will go to pretty long lengths to avoid the headline "Called the police for help, got fined".
*We got separate numbers for police, fire and medical.
35 minutes in now, still nothing.
The future I believe. Hang on, let me check, brb.
Re: Taking out meteors
If an object is big enough the atmosphere doesn't really affect it much. Most of it will reach Earth regardless. If you break it up into a few pieces the individual pieces would still be so big that they would reach the surface fairly intact. Thus you have you made your problem worse.
If you break it up into a large number pieces where all the pieces are so small that they burn up before impact or at least have a significantly part torn of then you would have lessened then problem.
I am not sure actually shutting it down would prevent a lot of the damage. The thing is that we are not talking about an EMP, but induction currents in wire. The longer the wire the bigger the current. This will thus not hit small scale electronics, but long wires. Of course any electronics which are attached to a long wire could get fried. So unplugging things could save them. The problem is that taking down the grid doesn't physically taking it down and cutting it up in pieces. So we could end up with frying the power lines themselves.
I do imagine that it is possible to save transformers and generators though by unplugging them from the power lines, if we are able to do that. And that would be a huge gain. Fixing the power lines would be a small job compared to that of winding new transformers and generators for the power plants and distribution.
Note 1: I am not sure about any of this.
Note 2: Except note 1.
By not being there.
The STEREO satellites are orbiting the sun at nearly the Earth's orbit. One is a little bit further out, the other is a little bit further in. This means that they are moving away from Earth in either direction. The idea is to be able to see the sun, and then flares, from different angles at the same time giving us a form of 3D view of the flares. So they survived the blast by not being hit by it due to being far away.
Download directly to Earth
Since the moon is tidal locked* to Earth and the maria are all on the side facing Earth, maybe we can just pick one that has line of sight from the bottom to earth?
Re: the Age of Miracles & Wonders
I have never understood the claim that we don't have flying cars. We have had them for years. They are called helicopters.
Re: Don't mean to be a cynic but...
I am pretty sure Mars' current geology rules that out.
First of all you are confusing statistics with mathematics. In mathematics we operate with certainties and there you are quite correct that all that we can know with a sample size of one is that all we actual know is that there is at least one thing to sample and at least one of the entire population has the traits of that sample.
But you see, that is where you have effectively argued that all sampling is meaningless. If there are a thousand black sheep on the field in Scotland all you know is that there is at least one field in Scotland, it has one thousand sheep and they are black on at least one of their sides. And so on. When you operate with certainties you will never know before you have sampled the entire population.
In statistics however you will try to quantify the different uncertainties. In science we can then use this to set certain thresholds to circumvent the problem that you often can only disprove certain things and never prove them. Basically all that we can know is that we are*, which makes it very hard to build a scientific foundation on.
Back to our sampling. I have never claimed and will never claim that if you take one sample that whatever qualities that has is the only one present in the population. To claim that I did by arguing against it is quite frankly something you should consider yourself too good for. What I am saying is that it is highly unlikely that you have found a unique entity in the population**. And this is what I mean with resolution. The bigger the sampling size the better resolution you get on the picture it casts on the entire population.
*Cognito ergo sum
**With regards to certain attributes. All humans are unique when you come down to it, and thus by selecting any individual out of the entire population you will never find any one equal. But that is not what you are after when you look at groups. You have to look at traits that are similar. Like how many legs, skin colour, reads the Register and so on.
Yes, helium are something we kind of jettison into space. Our current usage liberate it prematurely from the crust and in a greater rate than it is replenished. So throw it in with my other exceptions. Still, I think a nearby gas giant is a better place to go than invade Earth to take over natural gas reserves (which is where most of our helium comes from I believe).
Others mention the Drake equation as a reply here, but all that really does is to replace one unknown as a product of unknowns. I am not saying it doesn't have a value, but it's value is with establishing what we need to figure out in order to estimate a number.
However when it comes to answering this question we are left with one observation. There is life on one planet. The question "Are we alone?" actually becomes what are the chance that this one planet we have observed is the only one with life? If you are a visitor in our universe and you pick out one planet from one planetary system from one galaxy and that planet has life, then you can out of a sample size of one say that life is very common. In contradiction to what quite a few people believe in statistics a sample size of one will reveal quite a lot about what you have sampled. The resolution is just quite bad. However, we are not a visitor that pick out a random planet. So that is completely negated by the fact that the one planet we are observing is the one we are on and that the only reason we are observing it is because it has life in the first place.
So we are back at square one. Or not quite. We can look at the probabilities of probabilities. Since we know nothing how probable the different probabilities we have to regard them as random. What is the likelihood of a probability that produces one and just one planet with life at a given point? Well, we are still in the unknown here, but I find it extremely unlikely. To put it another way. Of all the results of the Drake equation the numbers of results that is not one is much much bigger than the results that is one. (The probability of the probability of each of those is not equal, for instance zero is probable bigger than the rest, but you get the idea.)
There is one problem though is that we are assuming one universe here. In a multiverse with infinite outcomes you suddenly make all the probabilities that is near zero valid again since all you need is for one of those universes to produce one instance of life at one point in time.
No, what we need to figure out how life started in the first place. Then we can establish how unlikely that was to happen when the conditions were right.
Re: Just waiting for EELT
You say close up. A dot or possibly two that represents that biggest planets out there is more likely.
Re: A quote from Hawking
Resources on a planet can for the most part never actually be used up. It is one of these layman views on the world and how it works that is simplified until it is plain wrong. There are a few exceptions. We could theoretically use up radioactive materials and some fusion materials like heavy hydrogen. Also we can in theory, but that will take a stupid amount of effort, take in use all of some of the elements present on the planet. For instance we could mine out all the gold and take it in use, but unless we start shooting it out into space or radiate it with particles to turn it into lead we will never use it up. Gold will forever be gold.
Chemical compounds such as oil and coal can be taken out of the ground and spent. Then we have to lower our consumption to whatever rate it is replenished, which is quite small, or we have to make it ourself. But since what we really get out of fossil fuel is energy and not the chemicals themselves*, we can get that from somewhere else. If there is one thing we do not lack, it is energy. At this particular point in time though we do have a somewhat limited supply of energy we are able to use. We are also quite bad at making use of the energy we do spend. However let us assume that if we were able to build ships that could send our entire species through space then we are also able to make decent solar panels.
Then we have such things as food and other resources we harvest. But that is just it, we harvest them which implies that there is a replenishing supply. We can screw up the supply by over harvesting, but it is a hell of a lot easier to regulate the outtake than to go to another planetary system, adapt an existing flora (in lack of a better word) or terraform to suit your needs.
Expansion and colonization is of course valid reasons to go out there, but using up the resources are just stupid. Resources are used not spent in a close systems such as these. Whatever Hawkins are thinking of I don't know and I haven't bothered to read up on it, but I have some much faith in the man that it is either something he just said as some thinking aloud, he just wanted to seed a discussion and spark an interest in the population or his argument is more complicated than that.
*The chemicals are quite easy to make if we have energy.
It is not as this new tech will enable us to see or take pictures of these exoplanets. In fact we will never be able to make technology that is able to do that from this system. There simply isn't enough data in the photons that reach us to do that. What we are doing is that we are creating instruments that is able to pry a little more data out of the few photons that do make it here.
We are not even able to take pictures of any decent quality of most of the planets, dwarf planets and moons in our own system. We have to send out probes to do it. Take Pluto for instance that we have not yet visited. Here is the best picture we have so far:
We can do of course is send probes, but I am sad to say that we will not be able to do that to other systems while I am alive. But we will get better pictures of Pluto next year. May 5, so clear your calender :)
So...we will be the blindfolded kid in the candy store. Dunno if that is worse or not.
From what I have learned from meddling with astrophysics two million is well within around a million. I would say around a million covers from two hundred thousand to five million.
What I can't figure out is how the same guys manage to do orbital calculations. I imagine the same does not apply when launching things into space.
Re: @ Loyal Commenter - not only, but also......
I am not so sure that four billion light years away in this setting doesn't mean distance to where the black holes were when they emi... didn't emit any light. In astronomy it makes just as much sense to speak of the light travel time distance as to talk about comoving distance. After all that is what you are actually observing, an object that is x billion light years away. The fact that it has moved a lot in the time light took to reach us and that space itself has expanded doesn't change the fact that we are observing something now that was x billion light years away then. If we suddenly should talk about where it is now we might as well talk about that it might not even exist either. Now I had said what I needed to say, under follows a rant.
It bugs me that they have buggered this up in the observable universe definition. It is in the name for <deity here>'s sake, observable. To talk about the comoving distance then is just mind-bogglingly stupid. We are not observing a 46 billion light year universe, we are observing a 14 billion light year universe. Where these things are now doesn't matter as we are not observing them as they are now anyway. If anything we should talk about the angular diameter distance which does factor in the expansion of space, but instead of projecting what we observe in the past into how it is now it tracks backwards to how far away we were at the time light where sent out. So it would make more sense to say that the observable universe is about three billion light years in every direction. However, I do think the muppets, fiddlers and semanticeers have settled this already I am afraid, so they can argue with people that don't care at parties about "No that is a misconception, the observable universe is 45,7 billion light years in radius, you see..." after that they will go on at lengths about how glass is either solid liquid or a liquid solid.
The thing is that when you talk about distance and you have several ways to measure it you have to actually tell us what metric you use. Once you do that any argument falls flat since it is in the clear what you mean. For instance measuring distances on Earth and you say "in a straight line" it usually means staying on the surface and not cutting through planet. But you can still go to parties and say "but a straight line doesn't curve so the distance between New York and Los Angles is really, yada yada".
As for your orbiting itself or each other comment, the sentence in the article makes perfect sense.
Re: different terminology please
Stop using the phrase low brow, it makes you sound elitist.
I am pretty sure that solar system is what you are thinking of. I was contemplating the same myself. However, I am unable to figure who actually decides what these words and expressions should mean.
Solar system: 1. The gravitational system of Sol. Usually referred to as "our" or "the" solar system. 2. A gravitational system of a star. Also named a planetary system.
Star system: A set of stars gravitationally bound together. Usually just a few, but the definition holds for what is usually referred to as star clusters and galaxies as well.
However, personally I would prefer star system as the general term of a solar system.
Re: Dunce hat
I want one! If I am qualified? I had to look it up, does that count?
Re: Core temperature @loyal commenter
I think you will find that the core temperature of a white dwarf is anything but equal to the surface temperature. I have not done the math on this, and I have only backed up my initial thoughts on the matter to the wikipedia article on white dwarfs, but it is quite simple.
1. If they are isothermic or close to it and you a have surface that is a few thousand Kelvin the radiation will be quite high as that is not far from an active star. Of course in total quite a lot less since the surface area is a lot smaller. But the heat capacity simply isn't big enough to keep this running for billions of years with a core temperature that is the same, even with it's big mass.
2. If the core at an active star is several million degrees and the surface only a few thousand, why would that change when it collapses after fusion stops?
Anyhow, white dwarf interior physics is not my specialty, but I find this bit from the wiki article not to contradict my limited understanding:
Although thin, these outer layers determine the thermal evolution of the white dwarf. The degenerate electrons in the bulk of a white dwarf conduct heat well. Most of a white dwarf's mass is therefore almost isothermal, and it is also hot: a white dwarf with surface temperature between 8,000 K and 16,000 K will have a core temperature between approximately 5,000,000 K and 20,000,000 K. The white dwarf is kept from cooling very quickly only by its outer layers' opacity to radiation.
So you are right it being isothermic, just that is has an atmosphere/surface that is not.
Its cold outside, there's no kind of atmosphere,
I'm all alone, more or less.
Let me fly, far away from here,
Fun, fun, fun, In the sun, sun, sun
*As for the original question what does 5000 times cooler mean, the closest I got was in total radiation. If you ignore the to the power of four bit in black body radiation you get that it's surface is about one ten thousandth and the temperature is about half.
You run the algorithm on sets of pictures on objects where you already have superior resolution pictures taken with better equipment. Then you compare, calibrate, try again until you can with confidence say that it isn't so. Kind of like what you do for any development cycle for virtually any technology.
Re: KBOs have not been seen close up? Come on pull the other one!
I am not sure comets actually qualify as Kuiper belt objects as they are not orbiting out there any more, as is the case with 67P/Churyumov–Gerasimenko as Rosetta is visiting, or their entire orbit is only partial placed in the belt. Besides they didn't use the term Kuiper belt object just Kuiper belt and comets are no longer part of it and thus no of the bodies out in the Kuiper belt has been seen up close. Then there is this small detail that the comets are more likely from the scattered disc and not the Kuiper belt, but we are now in a region of astronomy which is largely unexplored which mean the definitions are still being hashed out. (What is what and if one is part of the other is apparently up to debate)
Regardless of all this. If you let comets be KBOs and also a part of the Kuiper belt and that we seen a few up close* they are still fundamentally different from the objects still out in the Kuiper belt. Being regularly so close to the sun that the surface melts and vaporises does change you a bit.
The meaning of the paragraph was quite clear to me. It is possible to add two pages extra to add layers of precision, but pedantry-proofing articles makes them unreadable.
*I don't think we actually have any close up pictures from Rosetta yet.
Re: RE. Re. Equilibrium
Er...I do think balloons needs the internal pressure to remain there once inflated, or am I missing something?
Re: X scale
I finally found a page that explained it properly. The letter scale is logarithmic, but the number is not.
Re: Increase tidal force?
I did consider that briefly and now I have considered in a little more. I actually think it doesn't matter.
Consider Earth. Disregard the fact that most of it is liquid, because it is too viscous to follow the tide. Look rather at the rather the water on top. It is has a low viscosity or is pliable if you want. Still, the tidal force isn't enough to increase it more than a few meters. And it doesn't matter which part of the mass that bulges as long as there is enough left of the pliable mass. So if Earth was instead made up of a perfect liquid with the same density as the Earth has now it would not have higher tides. Gravitational force will reach an equilibrium against the tidal forces and the centripetal force from the spin.
Increase tidal force?
Gongjie Li [...] says: first, the expanding star will heat the planets, boiling off their atmospheres, while increasing solar tides will stretch the planets into egg-shapes.
I really don't get this. Tidal force is a result of gravitational force. Gravitational force is not in any way affected by the radius of the body that exerts it. The only two factors that matter is the mass of the body and the distance you are from it's center of mass. If you are moving into something that can be considered uniformly distributed along each distance to the center. As you can when you dig into an actual body or as you progress towards the center of a spiral galaxy. You can discard all the mass that is further out than yourself and only consider the mass that is closer than yourself to the center to calculate the net gravitational force you are experiencing. It does not matter whether all the matter on the inside of yourself is condensed into a perfect hollow sphere* you are a millimeter away from or that if all of the matter is condensed into a point in the center. The gravitational force you experience is the same.
Since tidal force is something you experience since a body actually has volume and thus parts of it will be further away from the center of mass of another close by body. This means the gravitational force on the particles it is made up of will be slightly different and this is in effect the tidal forces.** But again, as long as there is space*** between the bodies and the mass remains the same the gravitational force will remain equal on each of those particles with regard to the volume of the both of them and thus the tidal forces will remain equal.
Please enlighten me if you see the flaw in my reasoning or what I didn't get from what Gongjie said.
*Assume a theoretical hollow sphere that has the same mass as the theoretical body we started with and that is infinitely thin. If you are unable to, assume it to be 1 mm thick. Both are equally impossible.
**Almost, but not exactly.
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