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Comment Re: growing orbital space junk problem (Score 1) 275

That depends on how the destruction is done. A good comparison is between China's destruction of Fengyun 1C in 2007 and the US' destruction of USA-193 in 2008. The former was done at a higher altitude than the latter. The former created 3425 catalogued(*) pieces of debris, some of which will remain in orbit for decades, whereas the latter created 174 catalogued(*) pieces of debris, none of which remained in orbit two years later.

Tiangong-1 is at a lower altitude than Fengyun 1C (perhaps obvious, since it's about to deorbit), so it's not out of the question for China to destroy it in a way that doesn't make a permanent mess. I'm not advocating that, I don't know whether that's a good idea, I don't know if China has the capability to do that, I'm just disputing your blanket assertion that it's an "absolutely terrible idea".

(*) I mean catalogued by the US military and made available unclassified. It's worth noting that the US military usually keeps orbital data about classified satellites classified. It seems to have made an exception for the debris of USA-193, perhaps for good public relations in discussions such as this one.

Comment Re:They calculated the results? (Score 5, Informative) 49

No, they performed a measurement. FTA:

"Ten years after ACTIVE began, ... more than three hundred met the criteria for dementia, but their odds varied significantly based on which group they had been assigned to. Among those who had been given no training whatsoever, fourteen per cent met the criteria for dementia. ... The comparable rate of dementia for the speed-of-processing group was slightly lower, at 12.1 per cent. And among those who had been invited to receive the additional training, 8.2 per cent developed dementia."

Comment Re:reforestation (Score 1) 174

>... it means giving up land that could otherwise be cultivated or developed. And that's something humans have never willingly done...

Perhaps you meant globally, and over many centuries. But in the US and since WWII you are wrong; we are willingly reforesting land that has previously been cultivated

From the linked article:
"Forest growth nationally has exceeded harvest since the 1940s."
"the average standing wood volume per acre in US forests is about one-third greater today than in 1952; in the East, average volume per acre has almost doubled."

Comment Re: expansion of space and dark energy (Score 1) 358

Hi bhagwad,

I think your post needs some clarification.

You wrote:
> After a while, space itself would expand meaning that the ruler will now be longer than what it was.

The expansion of space must be measured with respect to something. The usual idea is that space is expanding with respect to other properties of the physical world, e.g., the mean distance between electron and proton in a hydrogen atom. So, because your hypothetical ruler is made of atoms, the claim is that tomorrow it will take more of those rulers laid end to end to reach distant galaxies.

In contrast, one kind of "ruler" that _is_ changing when space expands is the wavelength of photons and other ultrarelativistic particles. If space expands by 1%, photon wavelengths increase by 1% (as measured w.r.t. your hypothetical 1 meter ruler made of ordinary material) and thus photon energies decrease by 1%. This change is the explanation for the redshift of light from distant galaxies.

> After a while, the space between the nucleus and electrons or within the nucleus itself will become too large, ultimately ripping apart for the fabric of reality itself.

I suspect you are referring to cosmological models that end with a "Big Rip". In these models, the amount of dark energy in a constant volume of space (as measured with an ordinary ruler) increases with time. Eventually, the density of dark energy becomes greater than the density of other kinds of energy, e.g., the binding energy of atoms. Then fluctuations in this dark energy will rip apart atoms.

Because the properties of dark energy are hard to measure, it is not yet clear how its density changes with time. The current so-called "standard model" of cosmology, Lambda-CDM, takes the density of dark energy as constant, and this assumption is consistent with our best current measurements. So, as far as we can now tell, we are not living in a "Big Rip" universe.

Comment Re:Units (Score 4, Informative) 69

The first link in the summary leads to the Orlando Sentinel, which links to the full video from the Universidad de Huelva. That video estimates "400 kg, 0.6-1.4 m object, 40 m crater, 61000 km/h, 15 tons of TNT". The first three are SI units, the fourth closely related, and the fifth... well, "tons of TNT" dates from the 20th century so how can we call it archaic? It's the Orlando Sentinel who translates into those archaic English units for US-ers such as myself. In the second link in the summary Phil Plait goes so far as to translate the crater size into football fields, but perhaps we shouldn't fault him as that standard unit is neither "English" nor "archaic".

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