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Talk:Theory of relativity (view source)
Revision as of 19:46, November 17, 2009
, 19:46, November 17, 2009→Comments on Newtonian Mechanics
::: You are correct that the reference is not specific about whether people thought this ''at the time,'' but what matters is what people think ''now''. To truthfully say that Newtonian mechanics predicts the deflection of light, that has to be the state of the theory today, and it isn't. We could truthfully write that Newtonian mechanics did predict the acceleration and hence deflection of light centuries ago, but that has long since been abandoned---not the least because if masses accelerated light, we'd see light zipping by at many different speeds.
::: You are correct that the reference is not specific about whether people thought this ''at the time,'' but what matters is what people think ''now''. To truthfully say that Newtonian mechanics predicts the deflection of light, that has to be the state of the theory today, and it isn't. We could truthfully write that Newtonian mechanics did predict the acceleration and hence deflection of light centuries ago, but that has long since been abandoned---not the least because if masses accelerated light, we'd see light zipping by at many different speeds.
::: Finally, you will observe that while people differed in ages past on whether there ''was'' Newtonian deflection, none of those cites show any debate or disagreement over the ''magnitude'' of it. The predicted deflection is either zero (today) or 2GM/rcc; there are no varying interpretations of physics that resulted in 1.5GM or 3GM or 4GM or 1.1GM. Yet this seems to be what the article is implying, in defense of the Newtonian prediction being wrong. UNSIGNED
::: Finally, you will observe that while people differed in ages past on whether there ''was'' Newtonian deflection, none of those cites show any debate or disagreement over the ''magnitude'' of it. The predicted deflection is either zero (today) or 2GM/rcc; there are no varying interpretations of physics that resulted in 1.5GM or 3GM or 4GM or 1.1GM. Yet this seems to be what the article is implying, in defense of the Newtonian prediction being wrong. --[[User:NgSmith|NgSmith]]
:::: What people think now is that Newtonian theory predict deflection of light. That is what all the sources say, and I don't know why you would say anything else. People now say that light has mass, that Newtonian gravity attracts light, and that light is deflected. [[User:RSchlafly|RSchlafly]] 10:59, 17 November 2009 (EST)
:::: What people think now is that Newtonian theory predict deflection of light. That is what all the sources say, and I don't know why you would say anything else. People now say that light has mass, that Newtonian gravity attracts light, and that light is deflected. [[User:RSchlafly|RSchlafly]] 10:59, 17 November 2009 (EST)
::::: People now say that light has mass? Who says that?
::::: No, the mass of a photon is zero, and so says every contemporary source I can find. Can we dig up a single textbook from the last 100 years, or in fact any reputable source, that asserts that a photon has mass?
::::: It is overwhelmingly clear that "what people now think now" is that light is massless, which therefore incurs no deflection under Newtonian gravitation. Indeed, we have long known that the speed of light is constant, and that alone contradicts the idea that gravity can accelerate or attract light; if that was true, then light from each star would be traveling at a different speed when it hit us, depending on the star's distance and mass.
::::: Granted, people might look at the equations for mass deflection, observe that the deflection is the same regardless of mass, and suspect that deflection may also hold for m=0, i.e. massless light. But while we may ''suspect'' that, the equations don't directly ''predict'' it. There is no equation in Newtonian mechanics that predicts a gravitational pull on an object of mass 0.
--[[User:NgSmith|NgSmith]]