Dark_anzel Posted January 15, 2009 Posted January 15, 2009 some scientist , during LHC experiment said that if we try to move the proton with the speed of light, it would be so heavy that it wouldnot reach the speed. is it possible?? if it was why does light exist??
NowThatWeKnow Posted January 15, 2009 Posted January 15, 2009 Since mass increases with speed you would have infinite mass that would need infinite energy at the speed of light. Do not confuse a proton with photon.
swansont Posted January 15, 2009 Posted January 15, 2009 Since mass increases with speed you would have infinite mass that would need infinite energy at the speed of light. This is a long-standing issue of definitions. Using the normally-used definition of mass (the invariant mass or so-called rest mass) this isn't true. It holds if you use a certain definition called the relativistic mass, but that causes other difficulties. What is true with either definition is that the kinetic energy's dependence on mass diverges at c, and then we reach the conclusion of it requiring infinite energy to do so.
NowThatWeKnow Posted January 15, 2009 Posted January 15, 2009 This is a long-standing issue of definitions. Using the normally-used definition of mass (the invariant mass or so-called rest mass) this isn't true. It holds if you use a certain definition called the relativistic mass, but that causes other difficulties. What is true with either definition is that the kinetic energy's dependence on mass diverges at c, and then we reach the conclusion of it requiring infinite energy to do so. So, two objects moving away from each other at .99c would see each other as rest mass plus the energy needed for relativistic speed for a total of relativistic mass. This is regardless of who accelerated away from who and they would see them selves as rest mass only. How do we tell who was the one that accelerated in the first place? The object that was at rest in the first place could accelerate away from the other object increasing the separation speed. The object that increased speed in the first place could not increase the separation speed without exceeding light speed. Another paradox that could be explained by an ether, or am I looking at it wrong?
swansont Posted January 15, 2009 Posted January 15, 2009 So, two objects moving away from each other at .99c would see each other as rest mass plus the energy needed for relativistic speed for a total of relativistic mass. This is regardless of who accelerated away from who and they would see them selves as rest mass only. How do we tell who was the one that accelerated in the first place? The object that was at rest in the first place could accelerate away from the other object increasing the separation speed. The object that increased speed in the first place could not increase the separation speed without exceeding light speed. Another paradox that could be explained by an ether, or am I looking at it wrong? I'm not sure what the paradox is here. If you have two observers moving away from each other at 0.99c, both observers will see this to be the case. To see this it doesn't matter who did the accelerating. To increase the separation speed one would have to add energy, and to calculate this use the proper equation, which diverges at c. Using the wrong equation might give you an answer that exceeds c, but that's not a paradox.
NowThatWeKnow Posted January 15, 2009 Posted January 15, 2009 I'm not sure what the paradox is here. If you have two observers moving away from each other at 0.99c, both observers will see this to be the case. To see this it doesn't matter who did the accelerating. To increase the separation speed one would have to add energy, and to calculate this use the proper equation, which diverges at c. Using the wrong equation might give you an answer that exceeds c, but that's not a paradox. Houston control sends the mother ship from Earth on a trip to a near by star. After accelerating to a separation speed from Earth of .99c they are at rest in their inertial frame. Since inertia says it will "stay in motion in a straight line unless acted on by an outside force", little or no power will be needed to maintain the separation speed. At this point we have symmetry between the Earth and the mother ship it it makes no difference who accelerated away from who. Space man Joe decides it it taking too long and gets into a secondary space ship and blast off towards the destination star at a separation speed from the mother ship of .99c. This would cause a separation speed from Earth exceeding the speed of light. Can you explain where I am going wrong with out complicated equations? (and you thought you got rid of me ) Welcome Dark_anzel
Sisyphus Posted January 15, 2009 Posted January 15, 2009 (edited) Houston control sends the mother ship from Earth on a trip to a near by star. After accelerating to a separation speed from Earth of .99c they are at rest in their inertial frame. Since inertia says it will "stay in motion in a straight line unless acted on by an outside force", little or no power will be needed to maintain the separation speed. At this point we have symmetry between the Earth and the mother ship it it makes no difference who accelerated away from who. Space man Joe decides it it taking too long and gets into a secondary space ship and blast off towards the destination star at a separation speed from the mother ship of .99c. This would cause a separation speed from Earth exceeding the speed of light. Can you explain where I am going wrong with out complicated equations? (and you thought you got rid of me ) Welcome Dark_anzel Even though, from either ship, they would be separating at 0.99C, from Earth the separation speed of the farther ship would still be less than C, and two ships would have a separation speed of less than 0.01C. The mothership would still be at 0.99c, and the secondary ship would be 0.9999C (or something). This is possible because the relative velocities of objects is dependent on the reference frame from which they are observed. Put another way, from your own perspective, you can keep accelerating indefinitely at the same rate, and you never get any closer to C (again, from your own perspective). From the perspective of someone in your starting reference frame, however, your rate of acceleration appears to slow down, approaching ever closer to C but never reaching it. Edited January 15, 2009 by Sisyphus
NowThatWeKnow Posted January 15, 2009 Posted January 15, 2009 Even though, from either ship, they would be separating at 0.99C, from Earth the separation speed of the farther ship would still be less than C, and two ships would have a separation speed of less than 0.01C. The mothership would still be at 0.99c, and the secondary ship would be 0.9999C (or something). This is possible because the relative velocities of objects is dependent on the reference frame from which they are observed. From a reference point on the mother ship, the secondary ship would get to their destination well ahead of them. The mother ship would arrive on time by their own schedule as calculated on Earth. Maybe not a fair comparison but we can sit here on earth and watch the distance between two distant galaxies increase faster then the speed of light. Are you saying because of time dilation the mother ship would arrive at the destination VERY shortly after the secondary ship (from the perspective of space man Joe in the secondary ship)? ...you can keep accelerating indefinitely at the same rate, and you never get any closer to C... Are you saying you would not get to your destination any sooner? If so, it would be wise to conserve power and shut down the engines and let inertia do it's thing.
swansont Posted January 15, 2009 Posted January 15, 2009 Space man Joe decides it it taking too long and gets into a secondary space ship and blast off towards the destination star at a separation speed from the mother ship of .99c. This would cause a separation speed from Earth exceeding the speed of light. Can you explain where I am going wrong with out complicated equations? Well, that depends on how you define "complicated" Speeds don't add linearly. Joe will be traveling at ~.99995c relative to earth. If we take a different example and use 0.5c for both the mother ship and Joe (instead of 0.99c), then Joe will be going 0.8c relative to earth. The nonlinearity of velocity addition is much reduced at low speeds, so at speeds we're used to experiencing we don't notice it. The equations are at http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html and there are calculators, too. The case that applies most directly is the third box, with the rocket sending out a projectile
Pete Posted January 16, 2009 Posted January 16, 2009 This is a long-standing issue of definitions. Using the normally-used definition of mass (the invariant mass or so-called rest mass) this isn't true. It holds if you use a certain definition called the relativistic mass, but that causes other difficulties. I believe that swansont is refering to what he believes are philosophical/conceptual difficulties, not physical ones. Merged post follows: Consecutive posts mergedsome scientist , during LHC experiment said that if we try to move the proton with the speed of light, it would be so heavy that it wouldnot reach the speed. is it possible?? if it was why does light exist??He's referring to particle's with a finite/non-zero proper mass. Light has zero proper mass so what he's saying does not apply to light.
NowThatWeKnow Posted January 16, 2009 Posted January 16, 2009 Well, that depends on how you define "complicated" ...The nonlinearity of velocity addition is much reduced at low speeds, so at speeds we're used to experiencing we don't notice it... The equations are at http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html and there are calculators, too. The case that applies most directly is the third box, with the rocket sending out a projectile I can relate to those equations but the calculator is nice. So this applies to two cars on I-40 also? Can you imagine how much time Isaac Newton wasted doing math long hand? Thanks for the link. This thread tells me that what appears to be a separation speed > C (between Earth and Joe) as observed by the mother ship is really an illusion. That makes me wonder about the apparent separation speed of distant galaxies and "The Universe" program scientist saying "the only thing faster then light is the expansion of space". Would one of you physics experts please tell me this is not easy to grasp so I do not feel stupid.
swansont Posted January 16, 2009 Posted January 16, 2009 This thread tells me that what appears to be a separation speed > C (between Earth and Joe) as observed by the mother ship is really an illusion. That makes me wonder about the apparent separation speed of distant galaxies and "The Universe" program scientist saying "the only thing faster then light is the expansion of space". Would one of you physics experts please tell me this is not easy to grasp so I do not feel stupid. The calculators only apply to local space, where special relativity applies. Once you get into regions of inquiry where General relativity applies, it's a different ballgame.
Sisyphus Posted January 16, 2009 Posted January 16, 2009 From a reference point on the mother ship, the secondary ship would get to their destination well ahead of them. The mother ship would arrive on time by their own schedule as calculated on Earth. Maybe not a fair comparison but we can sit here on earth and watch the distance between two distant galaxies increase faster then the speed of light. Are you saying because of time dilation the mother ship would arrive at the destination VERY shortly after the secondary ship (from the perspective of space man Joe in the secondary ship)? No. From the perspective of both ships, there would be a large velocity between them. From the perspective of Earth, the velocity difference between the two ships would be small. Are you saying you would not get to your destination any sooner?If so, it would be wise to conserve power and shut down the engines and let inertia do it's thing. Yes, you would get to your destination sooner. You just wouldn't get any closer to C. The speed of light is always always always the same in all directions, no matter what reference frame you are in. You can never say "I'm moving almost as fast as that light beam," because from your perspective, the beam is still moving away from you at C. Only otherobjects can appear to be moving at some fraction of C. And from the perspective of that other object, you are moving at some fraction of C.
mabsj2 Posted January 16, 2009 Posted January 16, 2009 i don't think its currently possible. photons have no mass that's why they can reach such immense speeds. however matter has mass which i think rules out the possibility.
NowThatWeKnow Posted January 16, 2009 Posted January 16, 2009 i don't think its currently possible. photons have no mass that's why they can reach such immense speeds. however matter has mass which i think rules out the possibility. Yes, in my first post in this thread I ended with "Do not confuse a proton with photon." I should have said: A photon (light) has no mass and a proton has mass and can not reach light speed. Merged post follows: Consecutive posts mergedNo. From the perspective of both ships, there would be a large velocity between them. From the perspective of Earth, the velocity difference between the two ships would be small. Could we say the Earth and Joe in the scout ship would have a similar view of the three objects (total separation <C)? But from the center mother ship there would be an illusion of a seperation speed between Joe and Earth >C? Yes, you would get to your destination sooner. You just wouldn't get any closer to C. The speed of light is always always always the same in all directions, no matter what reference frame you are in. You can never say "I'm moving almost as fast as that light beam," because from your perspective, the beam is still moving away from you at C. Only otherobjects can appear to be moving at some fraction of C. And from the perspective of that other object, you are moving at some fraction of C. I understand part of what you are saying but lets say we send two ships to our neighbor star 4 light years away. Ship one accelerates to .99c and then lets inertia maintain its speed (we only allow power to maintain .99c if gravity or space dust slows it down). Ship two leaves at the same time but maintains full power for the entire trip. However, it never exceeds light speed. Approximately how much time do both trips take as observed from each frame? If there is a link that describes this concept for the layman, I would be happy with that. No one answered my question: Would one of you physics experts please tell me this is not easy to grasp so I do not feel stupid? Maybe I don't want you to, depending on the answer. I do thank you and everyone else that helps the layman in this forum.
swansont Posted January 16, 2009 Posted January 16, 2009 Could we say the Earth and Joe in the scout ship would have a similar view of the three objects (total separation <C)? But from the center mother ship there would be an illusion of a seperation speed between Joe and Earth >C? It's not an illusion. The restriction on being less than c is only for two objects. If I see an object going at at 0.75c to my right, and at 0.75c going to my left, they are separating at 1.5c. To each other, though, they are separating at 0.96c, and none of our clocks are running at the same rate. I understand part of what you are saying but lets say we send two ships to our neighbor star 4 light years away. Ship one accelerates to .99c and then lets inertia maintain its speed (we only allow power to maintain .99c if gravity or space dust slows it down). Ship two leaves at the same time but maintains full power for the entire trip. However, it never exceeds light speed. Approximately how much time do both trips take as observed from each frame? If there is a link that describes this concept for the layman, I would be happy with that. You'd have to know the acceleration to come up with a numerical answer, and the math gets messier. http://en.wikipedia.org/wiki/Time_dilation#Time_dilation_at_constant_acceleration edit: I can't yet vouch for the veracity, but check out this calculator, and the "long relativistic journey" section http://www.cthreepo.com/cp_html/math1.htm No one answered my question: Would one of you physics experts please tell me this is not easy to grasp so I do not feel stupid? Maybe I don't want you to, depending on the answer. I do thank you and everyone else that helps the layman in this forum. This is definitely not an easy topic to grasp.
Sisyphus Posted January 16, 2009 Posted January 16, 2009 Could we say the Earth and Joe in the scout ship would have a similar view of the three objects (total separation <C)? But from the center mother ship there would be an illusion of a seperation speed between Joe and Earth >C? Yes, that would be right. I understand part of what you are saying but lets say we send two ships to our neighbor star 4 light years away. Ship one accelerates to .99c and then lets inertia maintain its speed (we only allow power to maintain .99c if gravity or space dust slows it down). Ship two leaves at the same time but maintains full power for the entire trip. However, it never exceeds light speed. Approximately how much time do both trips take as observed from each frame? The trip would be almost the same from the reference frames of Earth and the destination (which I guess is actually the same reference frame), but quite different in the two ships' reference frames. The crew of the constantly accelerating ship would experience much less time. Exactly how much would depend on the acceleration. BTW, in case it's not clear, I'm basically a layman, too, so don't take anything I say as authoritative...
NowThatWeKnow Posted January 17, 2009 Posted January 17, 2009 ...If I see an object going at at 0.75c to my right, and at 0.75c going to my left, they are separating at 1.5c. To each other, though, they are separating at 0.96c, and none of our clocks are running at the same rate.... This is definitely not an easy topic to grasp. The two calculators from you and one from Martin will let me come up with paradoxical #'s that I will just have to accept. I am glad you said it is not easy to grasp. However, the pieces of the puzzle are slowly coming together. Thanks Merged post follows: Consecutive posts mergedBTW, in case it's not clear, I'm basically a layman, too, so don't take anything I say as authoritative... What is clear is that you are a lot closer to working in a rubber room with raw meat for lunch then I am. Thanks Dark_anzel, Didn't mean to hijack your thread but it is all about light speed.
Martin Posted January 17, 2009 Posted January 17, 2009 (edited) ... However, the pieces of the puzzle are slowly coming together. that sounds hopeful, and as if the best thing for me is not to say anything and let this natural process continue of fitting pieces and getting used to. Sometimes it's better not to interrupt because yet another explanation at the wrong time can throw one off track However you also say this The two calculators from you and one from Martin will let me come up with paradoxical #'s that I will just have to accept... The calculators I link to are cosmology calculators. They embody the mainstream cosmo model. Cosmo is quite different from SR (special relativity). In some ways cosmo is a lot simpler. You can do almost everything (all the basic stuff) with just one clock. There is a universal idea of being at rest---at rest with respect to the CMB. On the other hand some people do get hung up with the fact that in cosmology large distances between stationary objects can increase faster than the speed of light. Sometimes they can get over the hangup by watching Ned Wright's balloon model animations for a few minutes. The galaxies are at rest because they stay at the same longitude and latitude forever, while the photons move wiggling along at about 1 millimeter per second across the face of balloon, traveling from one galaxy towards others passing by still others. And of course their are pairs of galaxies which are separating at much faster than 1 millimeter per second. No galaxy breaks the local speed limit because they are all standing still. A galaxy could never catch up with and pass a photon! SR is about a fixed static geometry, technically known as flat. GR says that if gravity were turned off, spacetime would assume a perfectly flat SR static geometry. SR is about one particular fixed static version of geometry. GR is the law that governs what geometries we get and how they morph. Because of gravity, and matter moving around, nature's real geometry is dynamic everchanging and flat SR maps only give an approximately decent fit in a limited locale. Like trying to tile a donut with flat square tiles. It doesnt work over large distances and it only works approximately even in small local neighborhoods. So SR and its famous speed limit work in local neighborhoods like the man whizzing past the earth in his rocket ship, smoking his cigar or bouncing lightbeams off mirrors or whatever. But SR does not govern the rate that largescale distances between stationary objects can expand. That is geometry changing. GR is a law of how geometry changes in response to matter. You have to let it do what it wants to do, because its predictions are accurate and successful. You can't argue with the donut just because the flat square tiles won't fit exactly. Or because one big square tile won't cover the whole thing. So there is kind of a division of jurisdiction: For the universe's changing largescale distances you use Ned Wright's calculator (google "wright calculator") and watch Wright's balloon (google "wright balloon model") or else you use Morgan's calculator (google "cosmos calculator"). And on the other hand, for local encounters involving the man in the spaceship passing by the earth, or two spaceships departing in opposite directions, you use SR or an SR calculator. Especially if gravity is comparatively weak so that the real geometry is approximately flat, and the SR flat approximation is applicable (which it usually is, in local matters.) I have the feeling that you already got over any problems with this, but since you pointed out the apparent disagreement of the SR and cosmo calculators I thought I'd say something. Edited January 17, 2009 by Martin
NowThatWeKnow Posted January 17, 2009 Posted January 17, 2009 that sounds hopeful, and as if the best thing for me is not to say anything and let this natural process continue of fitting pieces and getting used to.Sometimes it's better not to interrupt because yet another explanation at the wrong time can throw one off track... So there is kind of a division of jurisdiction: For the universe's changing largescale distances you use Ned Wright's calculator (google "wright calculator") and watch Wright's balloon (google "wright balloon model") .... I have the feeling that you already got over any problems with this, but since you pointed out the apparent disagreement of the SR and cosmo calculators I thought I'd say something. Martin, Your post are always welcome and helpful but when good information is flowing you can recharge your batteries for when it is needed. You pointed me to the Wright calculator and I am very comfortable with it. The #'s it gives are very believable. I am not in disagreement with any of the calculators but Earth logic has to be ignored when you use some of them. An accountant saying .75 + .75 = .96 could end up in jail. SR and time dilation are still awkward at times as you can tell from my post. I feel better about it every day and with an effort on my part and a little help from you guys I will get there. My goal is to answer more questions then I ask. 1
D H Posted January 17, 2009 Posted January 17, 2009 I am not in disagreement with any of the calculators but Earth logic has to be ignored when you use some of them. An accountant saying .75 + .75 = .96 could end up in jail. Earth logic is quite consistent with the relativistic velocity addition rules. [math]v = \frac {v_1+v_2}{1+v_1v_2/c^2}[/math] For [math]u,v\lll c[/math], the denominator is nearly equal to 1. Thus as velocities become small our Earthly logic rules ([math]v=v_1+v_2[/math]) become very close to correct. For small velocities, the simple addition rule overstates the relativistic addition rules by a factor of about [math]1+v_1v_2/c^2[/math]. Example: A pair of jet fighters flying straight toward one another, each traveling at Mach 1 (1225 km/hr) have a relative velocity of 2450 km/hr by the Galilean transform and by the Lorentz transform. The difference between the two is 3×10-9 km/hr: Immeasurably small.
iNow Posted January 17, 2009 Posted January 17, 2009 I'm not sure if this will help you, NowThatWeKnow, but it helped me. A short flash tutorial: http://faraday.physics.utoronto.ca/PVB/Harrison/SpecRel/Flash/TimeDilation.html
swansont Posted January 17, 2009 Posted January 17, 2009 I am not in disagreement with any of the calculators but Earth logic has to be ignored when you use some of them. An accountant saying .75 + .75 = .96 could end up in jail. Yes indeed. Relativity (and quantum mechanics) are not logical by the standard of everyday experience. That's one of the hurdles to understanding it. It's not intuitive when you start learning about it, and it can be a long row to hoe before any of it even starts to become intuitive. Physics is also not just math or accounting. In accounting you have rules, but you can make up new ones. In physics, we are bound by how nature behaves, and have to deduce the rules empirically. Merged post follows: Consecutive posts merged Like trying to tile a donut with flat square tiles. It doesnt work over large distances and it only works approximately even in small local neighborhoods. I like that analogy and can't recall having heard it before. You can use SR on any one tile, but as soon as you start comparing two tiles, GR applies.
NowThatWeKnow Posted January 17, 2009 Posted January 17, 2009 (edited) Earth logic is quite consistent with the relativistic velocity addition rules. [math]v = \frac {v_1+v_2}{1+v_1v_2/c^2}[/math] You make a good point. If Earth logic was on a scale that we could observe it, we would be much better prepared to understand relativistic velocity. Merged post follows: Consecutive posts mergedI'm not sure if this will help you, NowThatWeKnow, but it helped me. A short flash tutorial: http://faraday.physics.utoronto.ca/PVB/Harrison/SpecRel/Flash/TimeDilation.html I have seen similar demonstrations but the power point presentation let me go at my own speed for better understanding. Thank you. I like your signature line and it is so true. Since you are an expert now could you confirm all four examples below are correct? The twin paradox revisited (Dick and Jane) 1. Dick takes a space trip at relativistic speeds and when he comes back to Earth he is younger the Jane. 2. Jane doesn't want to be old so she takes a similar space trip and comes back the same age as Dick. 3. Jane wants to be younger then Dick so she starts off an a space trip. Some time later Dick decides he doesn't want to be older so rather then wait for Jane to turn around and come back, he jumps in his space ship and goes to her. They are the same age? 4. They both want to be younger and take off an similar space trips but in the opposite direction. When they get back they will be the same age even though they were in different inertial frames the entire trip. Is that right? The separation and closure during the trip was equal. My head hurts now. Merged post follows: Consecutive posts mergedYes indeed. Relativity (and quantum mechanics) are not logical by the standard of everyday experience. That's one of the hurdles to understanding it. It's not intuitive when you start learning about it, and it can be a long row to hoe before any of it even starts to become intuitive. Physics is also not just math or accounting. In accounting you have rules, but you can make up new ones. In physics, we are bound by how nature behaves, and have to deduce the rules empirically. Working and understanding the math (concepts) is hard enough but having the logic and aptitude to come up with the math and concepts is amazing. Edited January 17, 2009 by NowThatWeKnow Consecutive post/s merged.
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