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## The Penzias & Wilson CMB discovery paper

For the final part of my series to commemorate the 50th anniversary of the discovery of the Cosmic Microwave Background (CMB), today I’m going to show the original papers announcing this momentous discovery to the scientific community. I should point out that I have taken these photographs to portray the historical context, even though it is not easy to read what they say. The papers have been scanned and are available online for free in both gif and pdf format, follow this link to get them.

The announcement of the CMB’s discovery came in two back-to-back papers in the July 1st edition of The Astrophysical Journal (see the front page below). On pages 414 to 419 Robert Dicke and his team from Princeton (Dicke, Peebles, Roll and Wilkinson, 1965, ApJ, 142, pp414-419) described the theoretical work they had been doing which predicted a relic radiation from a hotter denser early Universe.

The front page of the July 1st 1965 volume of Astrophysical Journal, in which the Penzias and Wilson CMB paper is to be found.

Figure 1 from Dicke etal. in which they plot the “possible thermal history” of the Universe. It is due to the high temperatures in the early Universe that blackbody radiation would have been emitted when the Universe changed from being a plasma to being neutral (“re-combination” or “decoupling”) – shown in this figure as happening when the Universe had a radius of $10^{-3}$ (one thousandth of its current size)

The part of Dicke etal’s paper in which they refer to Penzias and Wilson’s observations.

Then, immediately following on from this paper, on pages 419 to 421 is the paper by Penzias and Wilson (Penzias and Wilson, 1965, 142, pp419-421). For the announcement of one of the most important discoveries in the history of science, both the title and content are very understated.
The title is A Measurement Of Excess Antenna Temperature at 4080 Mc/s, hardly a title to grab the attention.

The beginning of Penzias and Wilson’s paper. It possibly has the most understated title of any scientific paper of such importance.

The paper is nearly entirely technical, detailing their experiment and the steps they had taken to ensure that they accounted for the origin of every signal detected, apart from the “excess antenna temperature” of the title. At the end of the first paragraph of the paper is the following sentence – their only reference to its possible origin.

The only reference to the possible explanation for Penzias and Wilson’s “excess antenna temperature” (i.e.. signal) is the line “a possible explanation for the observed excess noise temperature is the one given by Dicke, Peebles, Roll and Wilkinson (1965) in a companion letter in this issue.”

The paper was submitted on the 13th of May 1965, as can be seen below.

The end of Penzias and Wilson’s paper, which was submitted on the 13th of May 1965.

Although the paper appeared in the July 1st volume of Astrophysical Journal, the New York Times had picked up on the story and ran its discovery as headlines in their issue on the 21st of May 1965. Although press releases of major discoveries are now often made when the paper is submitted, I would imagine it was rather unusual in the 1960s for scientific discoveries to be published in the popular press before the journal article had appeared. Does anyone now of other examples from this time and before?

A rather fuzzy screen capture of the front page of the New York Times from the 21st of May 1965

And this is the actual article, from the New York Times archives (one has to pay to get such articles, but it is not much).

The actual article as it appeared on the front page

The remainder of the article from the 21 May 1965 edition of the New York Times on the CMB’s discovery

That concludes my series to mark the 50th anniversary of this most important of discoveries. If you want to read far more about the history of the CMB’s discovery, as well as its 1948 prediction and what we can learn from it, then check out my book by following this link.

My book “The Cosmic Microwave Background – how it changed our understanding of the Universe” is published by Springer and can be found by following this link.

## The CMB: how an accidental discovery became the key to understanding the universe

Over the last couple of weeks I have been writing about the Cosmic Microwave Background, as this month of July marks the 50th anniversary since the paper announcing its discovery was published. In this blog here I showed the original 1948 paper in which Ralph Alpher and Robert Hermann predicted its existence, and in this blog here, I re-posted something that I had written back in April 2013, before I had started research for the book I have published on the CMB.

Today I had been planning to write about its accidental discovery by Bell Labs astronomers Arno Penzias and Robert Wilson, but on Thursday of last week I had the following article published in The Conversation, if you follow this link you can read the original article. This article obviates the need for me to blog about the history of the discovery, you may as well just read it in The Conversation.

This article on the Cosmic Microwave Background was published in The Conversation last Thursday (23rd July 2015)

However, what is contained in this article is a summary of an even-more fascinating story, which you can read about in all its wonderful detail in my book, which can be bought directly from Springer, or from other booksellers such as Amazon.

My book “The Cosmic Microwave Background – how it changed our understanding of the Universe” is published by Springer and can be found by following this link.

To finish up this series on the CMB and its discovery, next week I will write about the Penzias and Wilson paper, and the accompanying paper by Robert Dicke and his Princeton team which attempted to explain the observation that Penzias and Wilson had made.