Q: Why do heavy objects bend space and what is it they are bending?

Physicist: Scientists can generally answer “medium complicated” questions.  The really hard ones are too damn hard, and the really simple ones are often “just the way things are”.  Or they may be really, really difficult questions in disguise.  You’ve found one of the fundamental questions that no one seems to have a good answer for.  We also don’t know why the mass, M, we use when talking about inertia (as in F = MA) is the same as the mass we use when talking about gravity (as in F = \frac{GMm}{R^2}).  The best theory I’ve ever heard is that matter is actually made of bunched up “knots” of space-time, and even that isn’t a terribly good a theory.

The second half of your question we do have an answer for, it’s just a little mind bending and hard to picture.  What heavy objects are bending is space itself. The way you detect space (follow me here) is with rulers or stretched out strings, or stuff like that.  Anything that measures distance.  Near heavy objects the distance between points is greater than you would expect, and you can use this fact to detect and measure the stretching of space.

The usual trick when trying to picture higher dimensional space is to knock off a couple of dimensions, and picture that instead.  3 dimensions is too complicated, and 1 is stupid, so here’s 2!

A circle and it's diameter in flat space

A circle and its diameter in flat space. Here D=6.5'', C=20.4'', and 20.4/6.5=3.13 ≈π.

A circle and its diameter in curved space

A circle and its diameter in curved space. Here D=7.2'', C=20.4'', and 20.4/7.2=2.83<π

Take the circumference, C, and the diameter, D.  You’ll notice that on paper (flat space) \frac{C}{D} = \pi.  Which makes sense, since that’s the definition of \pi.  However, on the balloon (curved space) \frac{C}{D} < \pi, since the diameter is longer.  This effect is huge (infinite) for things like black holes, but for an object like the Earth the effect is tiny (ignore the hell out of it).  The stretching of space caused by the Earth’s gravity (well… that is Earth’s gravity) increases the diameter of the Earth by about 18mm.

That is, the diameter you get by measuring the equator and dividing by \pi (D = \frac{C}{\pi}) is the “flat space diameter”, the diameter you get by physically dropping a rope through the planet is the true, “curved space diameter”, and the difference between these two is 18mm.

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43 Responses to Q: Why do heavy objects bend space and what is it they are bending?

  1. Pingback: Q: How far away is the edge of the universe? « Ask a Mathematician / Ask a Physicist

  2. Kishore says:

    Hi, I have a question regarding Space warping. Per Einstein, “space-time fabric” gets warped by massive objects and if these massive objects are twisting / rotating in space-time, then they could drag space-time along with them. What I would like to know is – isn’t space enveloping these objects all around? In other words, instead of imagining these objects to be located “on” space-time, shouldn’t we think of them as being enveloped by space-time in every possible direction, in which case, they should “warp”/”dent” space-time in all directions and not just on one side which means, for all intents and purposes, there are no dents ergo no gravity?

  3. The Physicist The Physicist says:

    I’m not sure I understand this question.
    While the warping of spacetime is certainly symmetric, if you’re near a star or planet or whatever, it’s still on just one side of you.

  4. Neil says:

    Regarding the question: How does mass warp [curve] space ? Could it be as simple as a massive object [like a planet or star] simply displacing space . The nuclei of the planet’s atoms would be responsible for the displacement of space . Hence a planet of higher density would warp space more than a planet of lower density [assuming both planets occupied the same volume]. The displaced space simply curves away from the planet . Space doesn’t appear to be empty if it accounts for most of the mass of the universe .

  5. The Physicist The Physicist says:

    Unfortunately the math doesn’t work out a cleanly as that, but I don’t have a particularly good intuitive argument against it.
    Among other things, energy also creates gravity, but doesn’t really take up space, and particles themselves (weirdly enough) don’t really have a “size”.

  6. orien rigney says:

    I’m an older dude with no professional training, but an electrician; purely by accident and determination. My question is: If in fact our universe began as a huge explosion that created space and matter simultaneously, why is it necessary to further confuse the mystery with time? To me time is a contrivance created by man to understand a bit better how long it takes to get from one point to another, not a necessity. If space on the other hand is actually physical as the Higgs is thought to be, there may be a problem. Until just a few hundres years ago, time was looking at sunrise, sunset and a stick in the ground to calculate the middle hours? At night, you slept until tiredness wore off from the previous day. Chances are we will not likely populate other solar systems for many generations and centuries, if ever? My thoughts are, we had best try finding ways to preserve this planet, rather than fool around with a universe we will physically never touch. And this while there still may be time.

  7. kristian Diaz says:

    doesn’t it make more sense that instead of bending the space like we see in picture it condenses space, by the matter not allowing space to be in that area. imagine a spider web that it gets more condense as you get closer to the center(matter) thats why it seems that time travels slower closer to the surface of the earth, because there is condense space. as opposed to away from matter where space and time are at equilibrium. and space pushes back into the matter creating the gravity we feel. and since it is all around, it creates the roundish shape of our celestial bodies?

  8. Lars wallin says:

    I have a question, a really interesting question about something I just cant figure out.

    http://m.youtube.com/watch?v=TxLUk1WJInk

    That is a video showing Hubble taking pictures of the Star v838 monocerotis emitting a light eco which makes the gas surrounding it visible like a brown sphere.

    If the star is bending space, why is its light-eco not bent? Why is the light traveling in a perfect sphere almost from it? If it is bending “something”, why is the light not bent also in its curvature?

    I mean, we learn that Space is “bent”, like a ball that bends something elastic. The star has a geometric curve around it in which smaller objects orbit. The curvature is like deep a valley, and the star is hanging in it at its center. But why does the light not travel in that curve, why does it not become curved? The light eco from this star is eMitting a sphere of light (as is showed by the light-painted gas of the light eco, which has the shape of a sphere).

    The only answer that I get in my head is that the object that bends space is bending “nothing”. But if it is bending nothing (empty space), how can another (smaller) object be pulled in the gravity of the bigger object? How can nothing make a object orbit something?

    Wow, that is a beautiful question. Please help me answer it!

  9. Lars wallin says:

    Speaking of heavy objects, why are galaxy cluster have galaxies that are gravitationally bound, but not superclusters (or so they say)?

    And to be rude, which me couriosity leads me too, you have not answered my question…

  10. The Physicist The Physicist says:

    The short answer is that an ordinary star barely bends space at all. You need pretty ideal conditions for gravitational lensing to become noticeable at all (huge distances and tiny angles).
    These light echos involve big angles (like, 90°) and relatively small distances (a few light years).

  11. Lars wallin says:

    Hi,

    So mean that öight would be bent “inside” the gravitional field, and then bounce out in to a almost perfect sphere? Hm.

    I asked my girlfriend the question. She said that the object must be bending space together, like a solarsystem of planets and stars together bends the space creating a sphere of gravity and not a “field”, and that the bent space is like a sphere and not flat (2d) as all animation shows. Think about it. It is nothingness (space) that becomes bent (you would perhaps say that there can be gas or other real material there, ergo there is something there; but these things excists in empty space)

    I know you physicians dont like pHilosophy, because it makes you think analytically and you like “meusure” things and not think about things as they really are.

    Now, the sun must (i think) bending space together with all other objects, and these objects also bends empty space in their orbit. That would explain why the heaviest object is in the center and dont become pushed away in by the total mass of all other objects: they work together to bend space, and the sund orbits around a heavier object, just like a biliion of other stars, the center of the galaxy, and now we have a “galaxy” – a lot of matter bound in the same gravitational field that together bends space.

    But I was also wondering why only galaxy clusters are do bend space together and not superclusters? And why not galaxy filaments?

    Do you know a good internet forum where I can ask these questions? And sorry for my spelling, I am a stupid Swede.

  12. Lars wallin says:

    I just came up with something more! If all objects are bending space together (which they are), then instead of “dark matter” (that matter we have invented because we think that a galaxy weight is less then it shows), then this “dark matter” can be two possibly other things.

    1. The heaviest object in a galaxy must be the center because everything in a galaxy is orbiting it. Then it is werry likely that we simply that know exactly how heavy this matter is. I mean that the center of galaxies weighs much more then we think.

    2. If we know exactly how much a galaxy weighs, and the center of the galaxy is not heavier then we think (theory 1),then perhaps are all objects, all galaxies, together helping to bend space, so a galaxy doesnt have a single gravitional impact, but is the result and weight of all galaxies that are proven to be bound together. Andromeda is contrebuting to our weight and all other galaxies in a superclusters (and perhaps even more then so?) are contrebuting to our weight, just like the planets in e solarssystem is contrebuting to its weight, and the solarsystem contrebuting to the weight of the galaxy, the galaxy to the weight of the galaxy cluster (and this weight together bends space, which it is proven that it does).

    This would mean that there is no dark matter.

    Now, you can say what you want, but if you really think about it, it is logical and werry likely so. What do you think?

  13. Lars wallin says:

    I meant that dark matter is the extra matter which we think must be there because the galaxy must have a weight that is more then we can see with our eyes. And perhaps is this extra weight a galaxy-core that is heavier then we think, or that all galaxies contributes to eachothers weight. Hence the object becomes heavier then we now can meassure. Or perhaps both? For both are possible.

  14. The Physicist The Physicist says:

    Clusters and super-clusters and everything else attract each other, it’s just that on a large enough scale the inflation of the universe becomes important, and is large enough to counter-act the attraction between galaxies.

  15. The Physicist The Physicist says:

    By watching the way stars in a galaxy move we can determine the distribution of matter, and we find that the bulk of the matter is distributed spherically, and diffusely through galaxies. There are super-massive black holes at the center of galaxies, but it generally accounts for very little of the total matter.
    If groups of objects some how shared mass, then we should see the effects all the way down to the level of our solar system (but we don’t).

  16. Orien Rigney says:

    Since I am neither a Physicist or a Philosopher, I can only retionalize things from the internet that make sense to me. While photons supposedly has a neutral charge, here is an experiment done with magnetism, with no space warping or bending by gravity.
    http://www.gizmag.com/synthetic-magnetism-stanford-photonic-crystal/25261/

  17. Nader Amirhosseini says:

    If black holes “Rip” or even severely stretch, bend and distort the fabric of space-time, then how come when they move through space, the space-time coordinates they leave behind is “magically repaired” and returns back to its previously undisturbed state?
    in other words the question is do we know how far the fabric of space-time can be distorted before the distortion remains permanent even if the object causing the distortion is no longer present at those coordinates? very much like a torn peace of fabric that remains torn.
    Thank you for your response

  18. rigney says:

    What if scienctist eventually find that space cannot be bent, ripped, torn or distorted, but an eternal continuum built specifically for this universe. Also, what if Black Holes are actually conduits back to the core of its beginning? Just a mad thought on my part.

  19. Troubled says:

    Each Q & A just keeps on topping the next. Bloody great read Haha. And to top it off now that we know dark matter exists, well……! But….Just a new question..Are we the center of the Universe or are we not?????

  20. rigney says:

    Science has influenced our lives for their betterment since its inception, but little has changed since many still believe the earth is flat and you can actually fall off its end. So, let’s not confuse these folks farther with things called dark energy or matter until we understand their function more clearly.

  21. Ross says:

    OK, so thanks to Einstein and Eddington we know space and time bends. But my question is a simple one.

    A black hole not only bends space and time, but turns it back in on itself. It does this in a perfectly (usually) 360 degree bubble of continuously exerted pressure. Space time (as far as we know) is infinitely stretchy.

    Doesn’t that mean that space and time is actually being ‘created’ within then black hole itself and wouldn’t you imagine, to something ‘evolving’ within the space time created inside the black hole that it would look terribly similar to a ‘big bang’? Our big bang for example?

    Given natures already proven track record for repetition (like we see in everything from fractals to leaves on a tree) wouldn’t it be natural to assume that a Universe could exist in every super massive blacks found at the centre of every galaxy and within those black holes the possibility for billions more?

  22. Ross says:

    PS.

    My next question is a more complicated one based on the last preposition.

    If a black hole has a bubble of space/time on the inside of it, which is at some point made completely isolated to the space time on the outside of it at the event horizon, what is/makes up/in the skin that separates them? Some kind of magnetic wall? Some kind of neutral space/time? Could that ‘skin’ actually be classed as space/time at all?

  23. rigney says:

    While I can’t argue the hypotheticals you mention as false, are any of them more than calculated theory? In a word, are they irrefutabvle fact? I agree, Gravitational Lensing is a known physical phenomena, but the rest, pure theoretical conjecture.

  24. The Physicist The Physicist says:

    @Ross
    Heavy objects do basically create more space, in the sense addressed in the post. For example, if you calculate the diameter of the Sun based on its circumference you’ll find that the actual diameter is a few feet greater. But the Sun isn’t continuously making new space, it’s just got that extra few feet.
    The “skin” of black holes is called the “event horizon”, because a lot of weird things happen there. Among other things time points inward as opposed to “toward the future”, which means that there’s no longer a nice relationship between how time passes at and below the horizon, and how time passes outside of the horizon.

  25. rigney says:

    While I’m no bible thumper, I believe the path of every galaxy, star, planet, moon or comet, right down to and including the last speck of dust in this entire universe, is controlled by a mechanism far greater than the sum of its parts. Is it a phenomena science considers nature? Maybe a small part of something considered a multi-verse system? Strings? Could we be only a hologram or dream? Or perhaps the grandeur of a SUPREME ENTITY of whom we can only hypothesize? To a well trained Physicist it is strictly a “No Brainer”. Simply put, how could galaxies or a planetary system such as ours exist or be explained, other than through natural processes? On the other hand, religion is faith beyond doubt. I don’ know how, but I personally believe our universe, along with all of its intrigue, was predicated long before its beginning. Since such a question will never be answered, science and religions may beat themselves into oblivion with philosophy and theory, but we will never be wiser than we were ten thousand years ago. Smarter? Maybe! But trying to put a name on an enigma that created our universe, plant and animal kingdoms as well as humans, underlies the unfathomability of this Entity.
    While I’ll not try using either Science or God to preamble my thoughts, how much do we actually know of our universe, or how much will we ever find out?

  26. Ross says:

    @The Physicist

    A black hole can be many billion solar masses and so that few feet of extra space time would be multiplied however many billion times; so much so that nothing escapes.

    I just find it a strange coincidence that cant be easily ignored.

    Our Universe starts as a small compact ball of super compressed particles/energy which (as we are told) expands beyond the speed of light (apparently an easily ignore science fact) into space/time which did not exist (there’s one of those ignored facts again, what’s creating the space/time? – was it there to begin with?) at all until the bubble of space/time we called the big bang started exploding.

    The we look at what we know. Frame dragging. Gravitational lensing. General Relativity. Event Horizons. The possibility of a billion miles of relative space from one perspective appearing to be no more than mile of normal, perfectly comfortable thank you, square space to someone within it. Because it’s ‘relative’ based on the forces of gravity effecting it.

    If we KNOW the Sun has that few extra feet, can’t we calculate how that would compare to the few billions solar masses of a super massive black hole and then compare that to the rate of expansion of our own Universe for comparison. Maybe there is a constant/formula? A place where a certain mass snaps space/time into two opposing but balanced forces? Didn’t I read there was a link between the mass of super massive black holes and the mass of their surrounding galaxies? A point where they stop feeding?

    All mind boggling stuff, but I’m sure we should be modelling more of what’s actually “beyond” a black hole, rather than just assuming that things end at the event horizon in a horrible incalculable mess.

    If the space/time within a black hole wasn’t stable, surely it wouldn’t be a black hole (then god help us).

  27. rigney says:

    I don’t understand much of our universe, but your veracity in asking questions about it makes me want to do the same.
    While there is accepted credence to some calculated guesswork, it is assumed to be simply that, guesswork. The three links below are quite interesting with well founded guesstimation far beyond my knowledge. Chemical analysis of certain elements give us reason to believe our universe is approximately 13 billion years old. But to calculate size and configuration of this same universe is simply a guessing game. The link explaining pulsars is extremely interesting since it speaks of an immense gravitational force holding a small ball of matter, approx. 25 miles in diameter, yet having a mass 1.4 times that of our sun while making one revolution on its axis in microseconds, is beyond comprehension. Since gravity is supposedly the weakest of the 4 basic forces, it makes one wonder why a compressed mass spinning at such a speed doesn’t fly apart? Anyway, this is how I get my information. Cheers!
    http://wiki.answers.com/Q/How_is_a_black_hole_detected#slideshow_catimages=callout_0.0
    http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html
    http://imagine.gsfc.nasa.gov/docs/science/know_l2/pulsars.html

  28. rigney says:

    You might be familiar with these links, but I find them rxtremely interesting because I lack the scientific knowledge of fully understanding their content. They may even give you a different slant on some things?
    http://www.newscientist.com/blogs/nstv/2011/07/how-the-universe-appeared-from-nothing.html
    http://www.pbs.org/wgbh/nova/space/how-big-universe.html
    http://blogs.discovermagazine.com/badastronomy/2009/05/07/the-universe-is-expanding-at-742-kmsecmpc/

  29. rigney says:

    I believe Spectroscopy is somehow used in determining the contents of an atom. But since I can find no constructive answers, without using the periodic table, how is an atom’s content determined through experimentation?

  30. Don says:

    For me, the notion of a mass bending space introduces the notion of spacial density. Far from the mass the density of space would be in its neutral state. As one begins to approach the mass the spacial density would decrease. Continuing towards the mass the spacial density would continue to decrease. Continuing on, at some distance from the mass the spacial density would begin to increase, pass through its neutral state, then increase to some maximum towards the center of the mass. Please comment. Where can I find more info?

    Next, what happens with light as it passes through this bent space? Is the speed of light fixed, period, or is it fixed relative to the density of space? Does the speed of light increase and decrease as the spacial density decreases and increases, respectively? Or, does the wavelength decrease and increase as the spacial density decreases and increases, respectively? Have the results been proven? Where can I find more info?

    If the wavelength changes as the spacial density changes, then how much do the masses in our solar system contribute to the red shift used by astronomers? Have such measurements been made to account for the positions and distances of the earth from the sun and planets? What are the results and where can I find more info?

  31. robk says:

    We have the mind-set that describes gravity as a warping of the substance of space as a result of matter and energy that is contained within it. My definition of space describes an absence of something and therefore seems illogical that this nothingness can be bent in some way. Perhaps the key words here are matter and energy. If we take concepts taken from Quantum Mechanic s we know that systems can be intertwined in higher special dimensions. Perhaps the phenomenon of gravitation is understood incorrectly. Maybe it is not how objects separated by distance bend the surrounding medium in-between them – perhaps the attraction is a result of the particles that they are made of being electrically bound to each other over higher dimensions that give rise to the illusion that the intervening space is being bent. I think the observation provides only one type of perspective as consciousness itself is not aware of the actual process that happen – we can simply make observations using our immediate experience and we are limited to dimensions in which we can freely think.

  32. Orien Rigney says:

    Until we fully understand the real “nitty-gritty” of what matter and magnetism are, gravity is only a well defined assumption. From Newton’s era until today, gravity has been formulated by many great physicist, foremost; Einstein. Yet we continue working in unknown territories of multiple dimensions and string theories. Documentation of gravity’s action and reactions are paramount in appearance, but that is about as much as we know. We are much closer to discovering the myth of the Higgs Boson than we are the actual function of what we presume to be gravity. As squirrely as it may sound, one day we will likely find that gravity is only another deep and mysterious manifestation of magnetism.

  33. MIKE DAMICO says:

    Thanks for taking the time to answer for us simple folks. My questions are 1) How do we know space itself is actually bending and that we’re not just seeing the effects of gravitational lensing from our point of view? 2) We see black holes depicted like a bath tub drain with things going in through an opening. Wouldn’t they really be a “black ball” where things could enter from any direction? Thanks again!

  34. tony simpson says:

    Surely people as brilliant as physicists are alleged to be, should be capable of articulating an answer to the following question: How can space, which by definition is the absence of matter, be influenced by anything? Einstein’s bowling ball on a trampoline fails because it is an apple and oranges comparison. The trampoline fabric is composed of atoms which are influenced by the bowling ball. Space contains no atoms – no matter – and therefore is not accurately compared to a trampoline fabric. They assure us that the math says so, but they, while able to comprehend such complicated calculations, are struck dumb when it comes to articulating their findings. Perhaps some additional courses in English Composition are in order.

    The same is true for their insistence on a Big Bang, whereby every bit of matter in the universe sprang into being from the utter absence of matter. Those who make incredible, seemingly impossible assertions, bear the burden of proof. And, I believe, the responsibility of articulating their argument so as to be intelligible to the average non-scientist of reasonable intelligence.

  35. Orien Rigney says:

    Tony, the darndest thing about science is that other than a hands on approach,
    they are all in the same boat as the rest of us, It’s a guessing game! This is
    especially true in trying to understand things beyond our own solar system. Such
    as calling gravity one of the main forces of nature. It’s a joke. Other than the
    calculations of Newton and a few tweaks from other great mathematicians, we
    don’t know squat about gravity. When full discovery is known, we may find that
    gravity is only another facet of magnetism. While the trampoline and bowling ball make a good demonstration of what is called space fabric, magnetism and
    and a universal constant speed makes more sense. When this universe came into
    being?, I believe it happened in a pristine continuum without blemish. I also
    believe the expansion was in all direction with the same velocity.
    Yes, fourteen billion years may have been needed to shape the galaxies,and solar
    systems as we see them today. Yet, each and every grain of dust, up and to include whole galaxies; regardless of their configuration in this universe, maintains a constant speed set for them those billions of years ago. But then, this is only my thoughts Tony. Nothing carved in stone.

  36. John Lindop says:

    Matter does not cause distortions in space / time , the distortions in space / time are matter.

  37. Orien Rigney says:

    John, as I read your statement, it seems to be a dichotomy of sorts. But then, perhaps I’m trying too hard, grasping at the meaning. If you are saying there is no distortion of space, I agree without question. Before the expansion of our universe a straight line could have been drawn through this continuum never to end in either direction. Now, only beyond this univese is that still the norm. Our problem with time is trying to use C as the only constant, when the word is only relevant to what is happning at a precise moment. Cheers!

  38. Sean Carpenter says:

    @The Physicist
    Can matter, at its most fundamental part, be defined as non-spacetime, where traditional physics like gravity don’t apply?

    And more conceptually, how can the skin of the universe be explained? I.e, if spacetime is within the universe (perhaps giving it shape), how is it different from the absence of spacetime beyond that wall?

    Furthermore, can the expansion/contraction of our universe be attributable to the ratio of finite energy as matter to radiation, since the more matter will create more gravity that will collapse space time (potentially a Big Crunch if all the energy in the universe were a singularity of matter with such devastating effects on spacetime that it would virtually cease to exist, supporting the notion that matter is non-spacetime)?

  39. Orien Rigney says:

    Since I fret about much that I don’t know, this should come as no surprise.

    CHRONOLOGY OF THE BEGINNING

    I’ve spent a day or so now musing a period following the Big Bang Theory when stars supposedly started forming. I’m not saying the time line is wrong following the “Dark Ages”, only that the sequence of what came first could possibly be skewed. The link below is NASAs own version of the periods of development.
    My take on it! When things had cooled to where quarks, gluons and other sub particles began forming atoms, I believe this vast universal sea of highly magnetized matter was transformed almost immediately into masses the size of “condensed galaxies”. Give it a minute to sink in. Think of one of your first k-12 experiments using a bar magnet, iron filings and a sheet of paper.” Zip”! All of the filings tried to pile up on the one pole when it was extended upward beneath the paper. No mono-poles back then either. Just head to tail, head to tail while forming daisy chains.
    I believe these giant orbs spun themselves into centrifugal dervishes, until flying apart, thus to form galaxies and then stars. Give me some feed back! Thanks

    The first intsant of time and forward. NASA
    http://www.nasa.gov/images/content/144789main_CMB_Timeline75_lg.jpg

  40. Miguel Margarido says:

    As a Physicist myself, I have to say I find the answers from “The Physicist” a bit odd – not just the wording (“weirdly enough”, ” a lot of weird things happen”, “bunched up “knots” of space-time”, etc) but also the notions being expressed. Maybe a matter of (awkward) style, maybe something else.

    Reflecting on what The Physicist posted:
    >> (“The short answer is that an ordinary star barely bends space at all. You need pretty ideal conditions for gravitational lensing to become noticeable at all (huge distances and tiny angles)”)

    …no.

    We do need some special conditions for the observation or detection of gravitation lensing, mostly due to how we observe astrophysical phenomena.

    But even average size stars like our own bend light and this is detectable. In the case of our sun, for instance, the shift/deflection caused by its gravity is about a 1000th of a degree, which is small but measurable and in accordance with General Relativity.

    Furthermore, the interaction between gravity and light also originates gravitational red shift.

    The following answer by The Physicist also requires some attention:

    >>” We also don’t know why the mass, M, we use when talking about inertia (as in F = MA) is the same as the mass we use when talking about gravity (as in F = \frac{GMm}{R^2}). The best theory I’ve ever heard is that matter is actually made of bunched up “knots” of space-time, and even that isn’t a terribly good a theory.”

    Well, we have to refer to the Principle of Equivalence, which is very much at the center of General Relativity:
    “An observer in a closed laboratory cannot distinguish between the effects produced by a gravitational field and those produced by and acceleration of the laboratory.”

    This principle has been tested and proven correct and follows from experiments that show that the inertial mass of an object is always equal to its gravitational mass.

    We also ought to touch on another related subject: gravitational waves, which were also predicted by General Relativity. For those interested, look up gravitational radiation and the pioneer work by Nobel laureates Taylor and Hulse, or papers on nearby pulsars and how double systems show with a pulsar in it give off gravitational waves and lose energy (with orbital periods being reduced due to it).

    All in all, I’d caution The Physicist on how he/she explains things. Honestly, the explanations given to people above don’t seem to be given by a real physicist at all.

  41. Xerenarcy says:

    @Miguel
    largely agree with what you say, though i am not myself a formally educated physicist (more of a personal interest bordering on obsessive).

    the big question i don’t see asked is ‘what is acceleration’.

    gravity and acceleration are indistinguishable to such a point it is arguable they are one and the same effect, both even have an event horizon that works (for all intents and purposes) exactly the same way. both effects are proportional to mass too, or is that not strange to anyone? another way to approach this… we transform gravitational effects into one of acceleration, so why do we not attempt the reverse, to claim that all traditional acceleration is the result of gravitational effects?

    the approach i am favoring of late is to treat acceleration as an entirely temporal effect. it is not that hard to imagine, actually, once you start to define gravitation as the deflection caused by varying rates of passage of time (similar thinking to snell’s law). in that sense gravitation is analogous to an ‘optical refractive index’ using different mechanics but essentially on the same basis – that light bends when its speed changes.

    under gravitation contexts, you are experiencing a constant acceleration, but not necessarily ‘moving’. changing altitude changes the constant acceleration rate, which in relativity is equivalent to changing the eccentricity of your hyperbolic path while maintaining a constant hyperbolic angle with respect to the curve’s center. it has been proven that the time dilation factor introduced by changing altitude from a massive body, is an independent effect from time dilation resulting from the speed of an orbit alone.

    since an acceleration is involved in changing velocity, and varying constant velocities have a gamma term for converting to and from proper time, it is hard to disagree that the acceleration is somehow related to the divergence of rate of time for the two frames of reference, moreso than their relative velocities. but that isn’t satisfactory… more accurately, acceleration appears to cause a change in the relative rate of time – however you look at it these two changes (acceleration, delta rate of time) are inseparable, and so comparing merely the velocities of objects seems ‘incomplete’.

    then, as far as ‘space bending due to mass’ goes, i disagree. it is not correct to say that only space bends, it is spacetime that must bend by definition. our inability to innately understand the effects of varying rates of time complicates this whole picture, so it is easier to explain acceleration in terms of a physical phenomenon (the stage has varying height) than a temporal one (the stage has varying friction). it is why i despise the ‘rubber sheet’ analogy for gravity; it is a geometrical description for a phenomena associated with motion (hence time) through space.

    to the point, when we are talking about uniformly accelerating frames of reference, i don’t usually (if ever) see an allusion to ‘space in a relatively uniform accelerating frame of reference is bent’. i can’t recall ever seeing such a conclusion, yet we assume that to be the case for gravity only…

    back to the friction analogy (in favor of a rubber sheet), it would make sense that objects will likely not follow straight lines while ‘sliding’ on a frictional gradient. that explains frame dragging and gravitationally induced rotations of orbiting bodies better than gravitational attraction in the literal sense, granted. however the same presumption taken here is assumed in relativity theory – that objects in one moment in time are one and the same in the next, and that this has an impact on how time affects motion.

    the very simplified concept here is that matter is dynamic in terms of time whether it is in motion or not – the underlying quantum states must evolve with time and local time gradients will affect wave propagation speeds asymmetrically, moving away and towards the ‘slowest point’ / center of mass.

    beyond this point i can only speculate, but it seems probable that this asymmetry creates a statistical (hence probabilistic) bias in the wavefunction favoring a direction towards the source of gravity (local minimum rate of time).

    the only outstanding unknown i can’t explain this way is the mechanism by which time (or space or both depending on the theory) is affected at range – what propagates this effect in an inverse-power law?

    again, i can only speculate here, but i suspect that the analogy of matter / mass being a knot of some sort in space time is more or less the right direction to take. the theory i’m favoring at the moment proposes that mass is an ideal carnot engine fueled by the passage of time (or instigating it depending on how you look at it), with leibnitz’ approach that all points in space gain their physical properties from their interactions with all other points in space (or reference frames, whatever you prefer to use, giving each a unique identity until proven otherwise; as opposed to the view that some frames of reference are equivalent and therefore irrelevant).

    to wind all that up… we aren’t sure if it is space that is distorted, or time, or both, by gravity. answering why heavy objects attract one another depends on what you’re distorting (perhaps not numerically but that’s not the point), and to make matters worse we simply do not yet know enough about what ‘time’ is and its full effect on space to even distinguish the different types of distortions…. spacetime is a nice concept but feels incomplete and oversimplified in its modern form compared to the range of phenomena it is supposed to account for (and doesn’t to the accuracy we’d like it to in the extreme examples; black holes, high energy particles, big bang, singularities, plank temperature, etc…).

  42. Suroj dey says:

    Is bigbang real??? is it possible that bigbang occured but after the universe was created?

  43. Orien Rigney says:

    While I have the utmost respect for peole gifted with math skills far beyond my level of uderstanding, I am not baffled by highly organized theories. Hiperbole is a very good method of rubbing snake oil on the unsuspecting with the thought it may work. But as an old adage puts it, “the proof is in the pudding”.
    Myself, I don’t give much credence to space warping or time diation as used today in trying to understand a mirage we reach for, but can’t quite touch, such as the B.B. Mountains of research have gone into providing viability to sustain this theory, but it may go by the wayside soon. Other than “Hands On” science, I am a total pragmatist.
    While something extraordinary happened those billions of years ago, perhaps there was no big bang at all, but only the whisper of a continuance. I’m a cyclical believer myself.

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