Cmac22

Not that it matters much but were you trying to say an object with a mass of a billion grams (or whatever)? because isnt weight a force affected by gravity and mass. so, after 100 billion years the gravity pulling the object would be much weaker because of expansion, and so the weight would decrease. just like our weight on the moon is different than weight on earth.

Im not really sure about this but i will take a stab at it. i looked up the definition and Wikipedia (sorry) says that ,"normal force is the component (perpendicular to the surface of contact) of the contact force exerted by, for example, the surface of a floor or wall, on an object, preventing the object from entering the floor or wall." it also says, "If an object hits the surface with some speed, the normal force provides for a rapid negative acceleration, depending on how flexible the floor/wall is" So from these two statements i suppose it is possible that the universe might reduce to small lumps. If these statements wernt true, then a moving object would not be stoped by contact force, and so would pass right through it. i suppose it would all gather up at a gravitational center. maybe it would be many small lumps i dont really know so dont take my word for it.

Hi. i just started physics this year so im not too deep into it yet. just had a question about center of mass. we were doing a centripetal force lab, spinning small weights on a string over our heads and varying the mass. so my question is: As your spinning the weights overhead, is the center of mass simply the midpoint between one end of the weights and the other end on the string (all the weights are the same). Or would the center of mass be at the end of the string. this is probly a stupid question but im just making sure.

Sorry, i have been sick for a while. alright this stuff (that martin has posted) has helped some. but there are still some unanswered questions, and i apologise. i understand that it is a hard subject to understand and you are doing your best and i appreciate it very much! So, distances between stationary objects, are expanding. and i think, correct me if im wrong, were talking superlarge scale here, stationary objects being galactic clusters. lets see....im forming new understanding right now as im typing so its hard to figure out what i dont understand haha. one quick question about expansion speeds. if distance A gives expansion speed B then does distance 2A give expansion speed 2B? thats kinda leading to my question about something martin said, "expansion speeds are larger than c (for any distance 14 Gly or larger)" is the reason for this the age of the universe? and what does this mean? if things 14 billion lys away are expanding faster than the speed of light does that mean we will never be able to see them? and another thing i still dont understand (and maybe im not supposed to understand just accept) is still about the ?edge? of the universe and the lack there of. if everything is "expanding" in every direction, then the universe must be getting bigger. i dont even know what im trying to ask here since i dont understand heh. i mean, if you looked at the universe as a whole, even though thats not possible since there is no edges (right?) then if you looked the next second, because of expansion, the universe must be the whole +1, in the sence of size.... i guess.... i dunno if any of this stuff that i have said/asked makes any sence. i know it doesnt to me haha. i think i need to read up on those other form topics the poll thread martin posted about expansion and so on. but if anyone could help it would be nice i gotta go to class now

thanks that helps some. but im still confused, i know the earth metaphor isnt perfect and all but i dont understand how the universe can be similar to a 2D serface like the earth... does this mean that space doesnt go off in every direction, or that if i go far enough one way i might end up at the same point? i know that sounds rediculos but its confusing and i understand the expansion of time part but isnt it also expanding physicly as well? and what does that mean anyways, that simply ratios between point a and b ar farther apart but relative to everything else its all the same? zzz so confusing! =========================== another thing i was reading one of the articals Martin posted: "the universe is self-contained. It needs neither a center to expand away from nor empty space on the outside (wherever that is) to expand into. When it expands, it does not claim previously unoccupied space from its surroundings." so how can it expand but not occupy new space? does this man its getting "bigger" in whatever way...yet still the same size or same amount of space????

alright. i think im starting to get the idea. but im definatly concidered a beginer in this whole subject. so i have a few questions that i could probably go around serching for the answers to but i have school work to do so help would be nice so....there is no edge to the universe, what does that mean, it goes on forever? and what is it that goes on forever? heres 2 more specifide questions 1. is there a point or an "edge" i suppose where there is no more "matter" or whatever past? like no more galaxies and stars, just...space i guess? and 2. if the universe is roughly 14 billion years old does that mean that we can only see things 14 billion lightyears away, and that there might be other things farther away but their light hasnt reached us yet? or is it a combo of the two? thanks

Thanks a lot martin. that is what i didnt understand.

But, Just because everyone sees expansion from their point of view doesnt mean that there is no center, does it?. take an explosion in mid-air for example. take any point in that explosion while it is still expanding. from that points point of view, "points" farther from the point of explosion are moveing faster, hence are expanding away. however, points closer to the point of explosion, are moving slower than the point you are viewing it from, so they appear to be moving away, when in reality they are moving in the same direction, only slower. in this example, any point you take seems to be the center because all the other points appear to be moving away from it. but its not. however there still IS a center, the point at which the explosion took place. i appologise if this sounds completely rediculouse but this is how i see it.

Thank you. yes this is what i was trying to say, and yes i view it similar to the fire cracker. if, as someone else mentioned, the Big Bang happened "Everywhere" then how could the universe be expanding? becuase if the Big bang happened "everywhere"...and it is expanding then there must be somewhere other than "everywhere" for it to expand into, right? and so...if this is the case i guess this "everwhere" would be more or less the center of the universe, and it would be expanding from there? no? if you got ideas on this please put them in, im not gonna be offended.

sorry, im very young and have a very limited understanding. but yes, i suppose i would be refering to the point that is equidistant from the "edges". i dont know if that would imply something beyond the edge. so, are you saying there is no edge to the universe and therefor no center? i was assuming that, if the universe is 14 billion years old, then light could only travel 14 billion years from whatever point it came from, and therefor that point would be the center and the extent of the light the "edges". i dont care about the exact point of the center of the universe. but as i understand it, one galaxy must be closer to the "edge" or unknown or undiscovered area of the universe, or the area that light has not yet reached. so, if you apply that in all directions shouldnt there be a general central area to the universe, the center of the area that light has expanded out to?

This has been bugging me lately. I was trying to find where the center of the universe is. I was dissapointed to find out that, as far as i have learned, there is no center. I have a little bit of understanding but need some help I remember something about the Big Bang occuring everywhere in space or time or whatever, and that in such extreme environments, the laws of the normal world might not hold, hence the uniform dispersion of heat. I have also read about the "ballon" metaphore used for the expansion of the universe. But it still doesnt make sence to me. If the universe is indeed expanding, in the sence that i understand it is(which may be wrong), then by going back in time it was once infinately small, bringing us to the big bang. so this infinately small whateveryouwanancallit must have been where the universe started, and should still exist? Someone please help me understand, im sorry if i was unclear. there is a lot of mixed info in there and most of it i dont fully understand