White noise vs Black body radiation - Physics Forums
Nov 4, 2009 - 2 posts
White noise vs Black body radiation in Classical Physics is being discussed at ... Why can we think the noise from human brain is white noise?
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Mathematical Physics of BlackBody Radiation - KTH
www.csc.kth.se/~cgjoh/ambsblack.pdf
Royal Institute of Technology
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by C Johnson - Cited by 1 - Related articles
The mystery of blackbody radiation triggered the birth of modern physics in 1900, when Planck .... But why is a lump of iron, the Sun or a human body thought of as an empty bottle with a ... place in the little pineal gland in the center of the brain.
Hi all:
I am confused about one question. When we detect signal from human brain using coil in Nuclear Magnetic Resonance, two source contribute noise to our signal. One is coil itself. The other is human brain. Why can we think the noise from human brain is white noise? Can we compare the noise generated by human brain with that emitted from black body radiation? I know for a resistor, we consider it as approximation black body for current. I hope to know what cause white noise of human brain? thanks for your help. xf | |||
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#2
Nov4-09, 08:44 PM
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P: 4,663
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The thermal noise across a resistor is called the Johnson or Nyquist noise. See
http://en.wikipedia.org/wiki/Johnson...3Nyquist_noise It is about v = sqrt(4kTBR) where k= Boltzmannn constant T = temperatore in degrees K B= bandwidth in Hz R = ohms Bob S A blackbody is a theoretical idealized object described as something ”ab- sorbing all incident radiation” commonly pictured as a cavity or empty bot- tle/box in which waves/photons are bouncing back and forth between walls at a certain temperature defining the temperature of the cavity. The bottle has a little peephole through which radiation is escaping to be observed, as indicated in the above common illustration of a blackbody. A blackbody is supposed to capture an essential aspect of the radiation from a real body like the visible glow from a lump of iron at 1000 C, the Sun at 6000 C or the invisible infrared faint glow of a human body at 37 C. But why is a lump of iron, the Sun or a human body thought of as an empty bottle with a peephole? Yes, you are right: It is because Planck used this image in his proof of Planck’s Law of blackbody radiation based on statistics of energy quanta/photons in a box. Planck’s mathematical proof required a certain set up and that set up came to define the idealized concept of a blackbody as an empty bottle with peephole. But to actually construct anything near such a blackbody is impossible. 9 10 CHAPTER 2. BLACKBODY AS BLACKPIANO It is natural to ask if with another proof of Planck’s Law, the concept of blackbody would be different, possibly closer to reality? This book gives a positive answer in a different proof of Planck’s Law with a different concept of blackbody as a lattice of vibrating atoms absorbing and emitting radiation as electromagnetic waves, which models a real body like a lump of iron, and not a fictional empty bottle with a peephole. We shall see that here is a close acoustical analog of a such a blackbody in terms of the strings and soundboard of a grand piano: a blackbody as a blackpiano! This shows the role of mathematics in the formation of concepts of the World: • With a strange mathematical proof the World may appear strange and incomprehensible. • With a natural mathematical proof the World my become comprehen- sible. Figure 2.1: Blackbody as a cavity filled with photons bouncing back and forth. Chapter 3 Interaction Light-Matter Light and matter are both single entities, and the apparent duality arises in the limitations of our language. (Heisenberg) What we observe as material bodies and forces are nothing but shapes and variations in the structure of space. Particles are just schaumkom- men (appearances).The world is given to me only once, not one exist- ing and one perceived. Subject and object are only one. The barrier between them cannot be said to have broken down as a result of re- cent experience in the physical sciences, for this barrier does not exist. (Schr¨odinger) One of the big mysteries of physics is the interaction between immaterial light and material matter, or in a wider context the interaction between immaterial soul/mind and material body. Descartes believed that the interaction soul-body took place in the little pineal gland in the center of the brain. Modern neurobiology does not give much support to Descartes’ idea but has not really any better theory and so the mystery of how soul and body interact remains to be resolved. What does then modern physics say about the interaction of light and matter? There are two competing theories depending on the nature of light as Deterministic electromagnetic waves described by Maxwell’s equations. Statistics of massless particles. 2. connects to Newton’s old corpuscular theory of light, which was revived by Einstein in 1905 after it had been declared dead and had been replaced by Maxwell’s wave theory in the late 19th century | |
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