Seeking Ultimates by Peter T. Landsberg

Author:Peter T. Landsberg [Landsberg, Peter T.]
Language: eng
Format: epub
Tags: Physics
Published: 2011-02-17T05:00:00+00:00

Quantum effects

151

1909

Planck’s first wife, Marie Merck, dies.

1910

Planck marries Marga von Hoesslin.

1913–1914

Planck becomes Rector of Berlin University.

1914

Einstein becomes Professor in Berlin, following a visit to Zurich by Planck and Nernst. Nobel Prize for Max von Laue (1879–1960).

1916

Planck’s son Ludwig is killed at Verdun.

1917, 1919

His twin daughters both die in childbirth.

1918

Planck, aged 60 years, receives the Nobel prize for physics.

1919

M von Laue (1879–1960), Planck’s student,

becomes Professor in Berlin.

1920

Chemistry Nobel Prize for Walther Nernst.

1922

Physics Nobel Prize for Albert Einstein (in Berlin 1914–1933).

1928

Schrödinger becomes Professor in Berlin as

Planck’s successor.

1929

Awarded the Copley Medal of the Royal Society of London.

1944

The second son, Erwin, was until 30 January

1933 a Secretary in the Chancellor’s office, and was involved in the anti-Hitler plot of 20/7/1944.

23/1/1945

Erwin is executed by the Gestapo.

6/5/1947

The talk between Planck and Hitler which took place in the spring of 1933 is the subject of a short note by Planck in Physikalische Blatter 3 1433

(1947).

4/10/1947

Death of Planck.

Returning to black-body radiation, we can now say: give me a black-body spectrum and I shall tell you the temperature of the emitting surface. For example, the sun’s spectrum above the atmosphere, which is approximately that of a black body, is at 5760 K.

We have to look now for the incompleteness; things cannot really be as pretty as that. In fact, there are many examples of experiments 152

Now you see it, now you don’t

yielding good approximations to the simple black-body spectrum described. The incompleteness resides here in the approximate nature of the agreement. However, we have also failed to consider that photons interact gravitationally with each other, so that we want to know the properties of the radiation, allowing for this effect. The results are then more complicated, see section 6.9 and [6.26].

6.8.2

Virtual pairs and the Casimir effect

Is energy really constant? Are there no exceptions? Is there no imperfection left? In fact quantum theory has given us the uncertainty principle, which implies a kind of intrinsic imperfection (using the term of Chapter 1). It dictates that, given a short time interval, the energy of a system is uncertain, and this uncertainty is greater the shorter the time interval. Nature is here a kind of bank manager: the more energy you want to borrow, the shorter the time for which she will allow you to have it. To this extent the classical notion of energy conservation actually fails. During these tiny periods of time particle–antiparticle pairs (see antimatter on p 50) may come into existence and then decay. They are called virtual particles or virtual pairs.

This must strike the reader as a profound change of tune. Is there a chance of perpetual motion of the first kind after all? No, since these violations of energy conservation last only for tiny periods. The state of lowest energy of an empty box can thus be pictured as a seething mass of particle–antiparticle pairs which are created and get annihilated all the time.

An empty box? This sounds like what we used to call a vacuum. It is indeed still a vacuum, but it contains this great activity even at the lowest temperatures.

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