Fact or inference? ..

The non amateur stuff. Hawking, black holes, that sort of thing

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brian livesey
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Fact or inference? ..

Post by brian livesey »

In popular astronomy literature, we see references to dark energy, dark matter, antimatter and virtual particles, etc. These phenomena are often presented in such a matter-of-fact way as to imply to the lay person that they actually exist, but do they?
I'm a lay person on these matters, but I happen to have a German son-in-law with a doctorate in quantum mechanics. Over the holiday period he came over to England and cleared up some misconceptions.
He assured me that there's no concrete evidence yet for the existence of virtual particles and antimatter. These supposed phenomena are inferences from previous data. At this point in time, they exist only as formulae. The same goes for dark matter and dark energy, and even black holes - nobody has seen a black hole directly, despite strong circumstantial evidence.
It goes to show that we should be cautious about some of the claims made by journalistic science writers. :wink:
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joe
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Re: Fact or inference? ..

Post by joe »

brian livesey wrote: He assured me that there's no concrete evidence yet for the existence of virtual particles and antimatter.
I read a little while ago that anti-matter had been isolated and trapped.

http://www.bbc.co.uk/news/science-environment-11773791

Does that mean that it exists?

"Dark" means unknown and, yes, black holes are inferred but most scientists in the field are confident that they exist given the evidence. I see no problems really. I read articles by sceptics and supporters alike but I suppose it pays to remind ourselves that we need to be careful about what is factual and what is inferred.
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big_kev
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Re: Fact or inference? ..

Post by big_kev »

brian livesey wrote:I happen to have a German son-in-law with a doctorate in quantum mechanics......He assured me that there's no concrete evidence yet for the existence of virtual particles and antimatter.
Antimatter has been seen to exist since the 1930's in the case of the positron, the evidence for this is as concrete as that for the electron.

"Virtual particles" by definition can never exist, if they do then they will no longer be "virtual" but will be "real particles".
brian livesey
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Post by brian livesey »

You mentioned the positron as an example of antimatter. Some years ago, I had a full body scan at the local hospital and asked the technician operating the machine what type of radiation was used. He said: "Antimatter". He then qualified this by saying that the radiation was positrons.
My physicist son-in-law told me that positrons are not antimatter.
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joe
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Post by joe »

If you read that BBC report I linked it says that scientists produced and trapped whole anti-hydrogen atoms.
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Post by Cliff »

Dear Brian, Joe and Big Kev,
Speaking personally from a lay-man amateur astronomer stance I think I can say I'm probably as sceptical as most about many aspects of current cosmology eg far from completely happy about dark energy and dark matter. Indeed if anything I think I'm happier with MOND or similar possible theories.
I also attended an interesting talk a few months back by a young cosmologist (not quite finished her PhD yet), who I was pleased to hear quite openly sceptical about "Hawking's Radiation" and felt pretty sure if it does actually exist it would be probably un-observable being very very weak.
However, that said, I must confess that even I feel reasonable happy about Black Holes. Even though BHs have not been seen directly, I think the fairly recently observed\imaged stars rapidly orbitting the "nothing" at the centre of our Milky Way seen are indicative of there being a Supermasive BH there. If I heard correctly they've even tracked one or two stars round a complete very small orbit.
So I think I accept that something as yet still un-observed very massive probably exists at the centre of the Milky Way and that something is probably\possibly a Black Hole.
Best wishes from Cliff
PS - What am I saying - me possibly believing cosmologists, I cann't believe it.
brian livesey
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Post by brian livesey »

Regarding the BBC report Joe. Producing "antimatter" at CERN isn't the same as saying that antimatter exists in nature. There are, as you know, human-made "elements" that last for only a moment.
Last edited by brian livesey on Thu Jan 27, 2011 9:36 am, edited 1 time in total.
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Cliff
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Post by Cliff »

Dear Brian et al
In my simple minded way I cann't help wondering if the very short lived new elements really existed at all or happened to be someting that conveniently (or possibly inconveniently) apparently produced very brief observable characteristics suggesting them to be some sort of new element ?
As for Black Holes, as I said before, I must admit, I'm now pretty well sold on their reality now, even though they haven't been observed directly.
Furthermore (assuming they do really exist ?) I am happy to believe Black Holes may never be proved to existby "ordinary" direct observation. As far as I'm concerned, the apparently actual observations of stars orbitting in small orbits at fantastically fast speeds around a "nothing" at the middle of the Milky Way is pretty well good enough for me.
However, as for Hawking Radiation and Evaporating Black Holes - yes and no! I treat them as mathematical possibilities.
Best wishes from Cliff
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Post by david entwistle »

brian livesey wrote:Some years ago, I had a full body scan at the local hospital and asked the technician operating the machine what type of radiation was used. He said: "Antimatter". He then qualified this by saying that the radiation was positrons.
Hi Brian,

I didn't know anything about full-body scans prior to reading this thread, but I assume you had a Positron Emission Tomography (PET) scan. Having read up on it, the technology is just astonishing. It's off-topic for this forum, so I won't go on about it, but invite anyone interested to read the wikipedia entry.

http://en.wikipedia.org/wiki/Positron_e ... tomography

As a result of the annihilation of positrons and electrons, in your body, your body was emitting 511 keV gamma ray photons, in pairs, each photon travelling in opposite directions. Quite amazing.
David Entwistle
brian livesey
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Post by brian livesey »

So that's why I glow at night! :wink:
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