Tagged Questions

1
vote
1answer
108 views

In Klein-Gordon, why should infinite downwards photon cascades be possible?

Here is a simple point about the standard interpretation of the Klein-Gordon equation that for the life of me I've never been able to understand: Why would the existence of true negative energy ...
4
votes
2answers
407 views

How was the Oh-My-God particle observed?

How exactly was the Oh-My-God particle (ultra-high energy cosmic ray) observed and its energy measured?
3
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2answers
289 views

How convincing is the evidence for dark matter annihilation at 130 GeV in the galactic center from the Fermi Satellite data?

I listened to Christoph Weniger present his results at SLAC today. See his paper is here: http://arxiv.org/abs/1204.2797 and also see a different analysis here: http://arxiv.org/abs/1205.1045. The ...
1
vote
1answer
2k views

Negative and positive energy and Hawking [closed]

I don't have any physics background (except the material we did in high school-long time ago). I was watching a documentary with Stephen Hawking about whether God created the Universe and I could not ...
1
vote
0answers
67 views

Cosmic radiation cutoff at LOW energies?

The energy spectrum of the cosmic radiation (not CMB) is limited to both sides. I know about the GZK-cutoff at high energies. Basically the interaction probability for photons of energies above 10^20 ...
3
votes
3answers
205 views

How scientists estimated that our universe is 4% normal matter, 21% dark matter, and 75% dark energy?

Is there a simple way to understand how scientists estimated/calculated the following percentages?
3
votes
6answers
194 views

Are there free data available online from cosmology (or astrophysics) experiments that anyone can analyse?

One can understand a subject better in physics by trying to solve as many problems as one can from a textbook say. When it comes to experimental physics and data analysis, no book on experimental ...
3
votes
3answers
467 views

Energy of the electron-muon reaction

Lets see the reaction: $e^- \mu^- \to e^- \pi^- \nu_\mu \;\;\;\;\;\;\;\;\;\;\; {(1)}$ I suppose, that this reaction occurs as follows $e^- \mu^- \to e^- \mu^- \pi^+ \pi^- \to e^- \pi^- \nu_\mu$ Is ...