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klotza submitted a new PF Insights post
A Hand-Wavy Discussion of the Planck Length
Continue reading the Original PF Insights Post.
A Hand-Wavy Discussion of the Planck Length
Continue reading the Original PF Insights Post.
There is a misconception that the universe is fundamentally divided into Planck-sized pixels, that nothing can be smaller than the Planck length, that things move through space by progressing one Planck length every Planck time. Judging by the ultimate source, a cursory search of reddit questions, the misconception is fairly common.
Ah, upon rereading the article, I see that you really pretty much hit on my issues in my last post.JDoolin said:Have you considered the idea of extremely high blueshift reference frames?
I have a common ordinary lightbulb producing wavelengths of light between 400 to 700 nanometers. However, from the point-of-view of a passing neutrino; with it's velocity negligibly below the speed of light, that same light bulb could be producing light with wavelengths less than the Planck Length.
So, perhaps the light from my lightbulb is producing a black hole in some frames of reference, but producing ordinary visible light in other frames of reference?
I'm highlighting the issue with a rather extreme case--the observer on the neutrino. Some people may argue that neutrino observers are not valid, because they have no ears, no eyes, and no souls, and that their reference frame doesn't exist. But consider if we took a light of wavelength JUST OVER the Planck length, and had one observer fly away from it, while another flew toward it. The observer flying toward it would find that the wavelength of the photon was smaller than the Schwarzschild radius of the photon's energy. But the observer flying away would find that the wavelength of the same photon was larger than the Schwarzschild radius of the photon's energy.
Well, I guess my point is that radiant energy-- E = hf = hc/lambda, is simply not the same as mass energy E=mc^2.
The mass has its own reference frame independent of everything else in the universe--mass is an intrinsic property. Also, being a black hole, or NOT being a black hole is an intrinsic feature of matter. The light only has a reference frame in reference to its source and its observer, and frequency and wavelength of light are extrinsic features--observer dependent... Relatively moving observers are going to measure different wavelengths of the same light, so if this idea is accurate, they would also disagree on whether the light spontaneously collapsed into a black hole.
I can't remember what it's called, even enough to search it via google, but there is actually a solution to this problem. The example provided on the wiki page that I remember used larger masses, as opposed to photons. Basically it says that as you approach the speed of light and pass a large mass, it can't turn into a black hole due to your reference frame. I really wish I could remember what it was called.JDoolin said:Have you considered the idea of extremely high blueshift reference frames?
I have a common ordinary lightbulb producing wavelengths of light between 400 to 700 nanometers. However, from the point-of-view of a passing neutrino; with it's velocity negligibly below the speed of light, that same light bulb could be producing light with wavelengths less than the Planck Length.
So, perhaps the light from my lightbulb is producing a black hole in some frames of reference, but producing ordinary visible light in other frames of reference?
I'm highlighting the issue with a rather extreme case--the observer on the neutrino. Some people may argue that neutrino observers are not valid, because they have no ears, no eyes, and no souls, and that their reference frame doesn't exist. But consider if we took a light of wavelength JUST OVER the Planck length, and had one observer fly away from it, while another flew toward it. The observer flying toward it would find that the wavelength of the photon was smaller than the Schwarzschild radius of the photon's energy. But the observer flying away would find that the wavelength of the same photon was larger than the Schwarzschild radius of the photon's energy.
Well, I guess my point is that radiant energy-- E = hf = hc/lambda, is simply not the same as mass energy E=mc^2.
The mass has its own reference frame independent of everything else in the universe--mass is an intrinsic property. Also, being a black hole, or NOT being a black hole is an intrinsic feature of matter. The light only has a reference frame in reference to its source and its observer, and frequency and wavelength of light are extrinsic features--observer dependent... Relatively moving observers are going to measure different wavelengths of the same light, so if this idea is accurate, they would also disagree on whether the light spontaneously collapsed into a black hole.
BiGyElLoWhAt said:I can't remember what it's called, even enough to search it via google, but there is actually a solution to this problem. The example provided on the wiki page that I remember used larger masses, as opposed to photons. Basically it says that as you approach the speed of light and pass a large mass, it can't turn into a black hole due to your reference frame. I really wish I could remember what it was called.
If I remember correctly (I very well could not), it has to do something with the geodesics of spacetime warping under the energy tensor from the relative speed of you and the mass you're observing. Now, this doesn't necessarily apply when we're talking photons. Darn my memory, and I'm only 23! I guess it's all downhill from here =/
Try to find any publication of the last 30 years using that concept.BiGyElLoWhAt said:Mass increasing is definitely included in some texts, so you're not losing that memory just yet! My first text that I read on SR had a thought experiment with 2 bouncing balls and 2 observers, and used it to demonstrate relativistic mass.
You would still get different pixels in each frame. To make it worse, if you transform pixels, the relation between (dilated) Planck time and (contracted in one dimension) distance does not hold any more.Ken G said:and volumes in 4-D spacetime are invariant, are they not?
mfb said:@JDoolin: That neutrino would need an incredible energy. Neglecting factors of 2, we have ##m_\nu m_P = 3 eV \cdot E_\nu## where the lightest neutrino mass is probably of the order of 1 meV.
Indeed it is.BiGyElLoWhAt said:Eisberg?
john baez said:To see how the calculation works, go here:
john baez said:Nice post! Another way to think about the Planck length is that if you try to measure the position of an object to within in accuracy of the Planck length, it takes approximately enough energy to create a black hole whose Schwarzschild radius is... the Planck length! So, one can argue that it's impossible to measure distances shorter than this - though the argument is a bit hand-wavy.
To see how the calculation works, go here:
http://math.ucr.edu/home/baez/lengths.html#planck_length
john baez said:..it takes approximately enough energy to create a black hole whose Schwarzschild radius is... the Planck length!...
Hint: compare the user name with the url.BiGyElLoWhAt said:That's not how I interpreted that link. It seems to me what the author is saying [...]
Hahahaha! Observation OP!mfb said:Hint: compare the user name with the url.
Sorry, could not resist.
john baez said:To see how the calculation works, go here:
http://math.ucr.edu/home/baez/lengths.html#planck_length
Last edited by a moderator: Yesterday at 1:24 PM
Aww, gee... thanks for the help......OCR said:http://math.ucr.edu/home/baez/lengths.html#planck_lengthFixed that for you.....
[/QUOTE]..[/QUOTE]...Last edited by a moderator: Yesterday at 1:24 PM
I'm not a fan of this theory, but there is an idea that spacetime is divided into pre-existing irregular grains of 1 Planck volume. This is called spacetime "glass" quantization, as opposed to "crystal" quantization should the grains be regular. The glassy properties of the quantization help it escape the usual problems with Lorentz invariance.Ken G said:On the topic of the "Planck pixel," perhaps this overall idea is being rejected too sweepingly. Presumably, the "pixels" would be in 4-D spacetime, not 3-D space, and volumes in 4-D spacetime are invariant, are they not? So I would imagine that if someone wanted to formulate a theory that said spacetime itself was parceled into "Planck pixels", they would play the usual game that in different reference frames, meaning along different world lines, the "pixels" would distort, but they'd still tile the spacetime in the same way. Yes that means objects don't "move one Planck length every Planck time", but that's obvious-- any such object would be perceived as moving at the speed of light. Instead, a "Planck pixel" idea could say that spacetime is discretely tiled, in the sense that world lines cannot be defined with finer precision than that-- similar to the way quantum mechanics "tiles" phase space in statistical mechanics.
Also, if we think of the "Planck pixels" as being in spacetime, their 1-D version also takes on some kind of meaning. If we choose c=1, it is often said that all objects seem to "move through" spacetime at a rate of 1 unit of spacetime displacement per unit of coordinate time. In that sense, an object could appear to move one Planck length each Planck time, and not seem to move at the speed of light, if the "Planck length" was interpreted broadly as also existing in the time dimension. It seems to me that could all be formulated in an invariant way, though its usefulness and/or ramifications I could not say. Most likely it would be some kind of "ultraviolet cutoff" to doing path integrals in spacetime, or some such thing.
Thank you for that insight. I would indeed think that if one wishes to regard spacetime as in some sense "coarse-grained" at the Planck scale, one must use a version of coarse-graining that is Lorentz invariant, meaning that the grains are defined by their volume but not their shape. This is hardly unprecedented-- the same thing is done to "coarse grain" phase space for statistical mechanical calculations, since there is no need to use a cubic tiling of "equal lengths" of distance and momentum when deciding how to count states. I don't mean to be unresponsive to the commenthaael said:I'm not a fan of this theory, but there is an idea that spacetime is divided into pre-existing irregular grains of 1 Planck volume. This is called spacetime "glass" quantization, as opposed to "crystal" quantization should the grains be regular. The glassy properties of the quantization help it escape the usual problems with Lorentz invariance.
I simply didn't understand it. It was my impression that volumes in spacetime would be Lorentz invariant, but perhaps there is something I am missing.mfb said:To make it worse, if you transform pixels, the relation between (dilated) Planck time and (contracted in one dimension) distance does not hold any more.
I (a complete physics idiot) actually posted a question that made the assumption that objects gained mass as they approached the speed of light. I was soon set right. Thank you for your explication, hand-wavey or not, of the Planck length, because I was a victim of the (erroneous) Planck-length = pixel size fiction as well.JDoolin said:I would probably go the other way... Obviously if your theory implies that something is turning into a black hole according to one observer, but is not turning into a black hole according to another observer, then your theory has been essentially discounted by reductio ab adsurdam.
I believe the problem is with the premise than an object's mass increases as it approaches the speed of light. An object's MOMENTUM increases as [tex]p = \frac{m}{\sqrt{1 - (\frac v c)^2}}v[/tex]; I feel that has been pretty well reasoned out. But the claim that an object's actual mass has increased (and hence it's capacitiy to pull other objects toward it by gravity) is NOT well supported by any reasoning I'm familiar with. I'm pretty sure I've seen this point made explicitly in some texts, but at 43, I'm well into my fifth decade of memory failure.
kalimaa said:As for myself I'm taking serious the idea, that all our established physical theories (including GR and QM) are effective theories in the sense, that they don't express anything fundamental about the ultimate nature of reality, but instead are approximations to the inner workings of reality in the discrete paradigm. Any thoughts?
The Planck Length is a unit of measurement in physics that represents the smallest possible length that can be measured in the universe. It is approximately 1.616 x 10^-35 meters.
The Planck Length is considered the smallest possible length because it is the point at which the fabric of space-time becomes so distorted that it no longer makes sense to talk about distances or sizes smaller than this scale. Beyond this point, the laws of physics as we know them break down.
The Planck Length was derived by physicist Max Planck in 1899 as a part of his work on quantum mechanics. It was later incorporated into the theory of general relativity by Albert Einstein in 1916.
No, the Planck Length is far too small to be measured with our current technology. It is also believed that it is impossible to ever construct a device that could measure lengths at this scale due to the uncertainty principle in quantum mechanics.
The Planck Length is significant because it represents the limit of our understanding of the universe. It is also a crucial part of many theories, such as string theory and loop quantum gravity, which attempt to unify the laws of physics at the smallest scales.