Eelpie

ok another way of putting the same question a different way.... if we had two objects where the expansion of the universe offset the extent to which they were gravitationally attracted to each other how would they behave? would tiny bits of space be created but then be pushed away by gravity so that the distance was unchanged? many thanks!

Thanks very much. I always thought that where two objects were in "equilbrium" wrt to each other gravity was typically predominantly offset by angular momentum? Or is it a combination It seems odd that it should exactly offset inside superclusters.... If we took two points in an "empty" bit of space ie between superclusters and these were 1m apart, then according to your formula and ignoring gravity (I am assuming points not particles with mass) after a billion billionth of a second space should have expanded but by less than a planck length. How is that possible? Or do we have to think in terms of quantum mechanics when thinking about small units of time? Is a billion billionth small?

sorry may have used terms like "local" wrongly...I know they have specific meaning in physics but I am using them as a layman would...also is relativity the right area for this post...I always assumed that general relativity was intricately related to theories about the expansion of the universe...

a naive question probably, obviously the expansion of the universe now in proportional terms is very very slow (would be interested to know how slow, how much further would an object exactly a billion light years away be after a year), but presumably even objects much closer together are moving away from each other and we could in principle observe the expansion of space? if the theoretical expansion between two points is below a planck unit how would it occur exactly?

how do you measure to 20 cm precision? has any one checked the speed of light recently? maybe its changed?

am i being too Bayesian if I think that this is more likely to be an experimental error than relativity is fundamentally wrong?

Apologies for replying twice last time (terrible internet connection and thought my previous post hadn't worked). The Swiss system involves excavating tunnels rather than building say overground plastic tubes. Clearly the former is sensible for a mountainous country like Switzerland but wouldn't tubes laid overground be cheaper in the UK? Are there cheap materials which would withstand the necessary pressures? "If I'm travelling in a tunnel at ~500 km/hr with a very complex system of equipment and infrastructure ensuring my safety, I won't be comforted by the knowledge that my mode of transportation was implemented using "...the cheapest way possible..."" Fair enough!

Thanks everyone for the responses. The C14 experiments I have found only look at DNA...does that mean the non-DNA parts of neurons are constantly being replaced? Could it be argued that although the majority of material in a brain cell is replaced after x numbers of years?

Using current technology probably yes but my challenge was to focus on the cheapest way possible of implementing a solution. Would it theoretically be possible to get the per km cost down to WCM levels or are the materials required inherently so expensive that it will always cost a multiple? New infrastructure can often be cheaper. The WCM was expensive partly because it wasn't new (it was also expensive because of bungling bureaucracy). The TGV line to Metz cost around half as much on a per km basis even though it was completely new. It became the fastest line in France (despite already having the fastest lines in Europe) and ended up nearly twice as fast as the WCM.

I think the authors control for that, also "natural" C-14 is tiny relative to anthropomorphic C-14 of the subjects tested.

Cheers just reading a slightly earlier paper by Spalding et al which makes broadly the same argument using carbon-14 analysis. It seems odd that the 7 year claim has become so ubiquitous when there is strong evidence for it not being true....

I found this: http://askanaturalist.com/do-we-replace-our-cells-every-7-or-10-years/ This is very different to what was said on "start the week" on BBC's Radio 4 this morning by a philosopher (I think) called Julian Baggini who claimed all the body was replaced... Would be interested in comments...

I agree that it probably would be a lot more expensive than the West Coast Mainline but saying it will cost many times does not really tell us much....from a materials perspective I could conceive it costing less...hence the under £30mn per km challenge. With creative thinking I am sure we can develop lower cost solutions, hence why we should look at partial vacuums and lower speeds. I wonder if an X prize would be a sensible way to stimulate research ie a prize for a team that was able to develop a system that would cost below £30 mn per km....we all know that projects led by large organisations particularly governments suffer from cost inflation hence the focus on would be the lowest cost system possible. It is not true to say that because it is a new infrastructure it will necessarily be more expensive. The West Coast Mainline was in part incredibly expensive because it was an upgrade of existing infrastructure. Even at the massively over budget level it did not deliver the orginal specification. £13bn delivered a marginal increase in speeds. By contrast a NEW line to Metz cost below £2.5bn at the exchange rates of the time (so a bit more than half the cost per km of the WCM upgrade) yet has top and average speeds at nearly twice that of the upgraded WCM. If Vacuum-Maglev cost say 6x the price per km of the Metz TGV (a complete guess) then we would be looking at a project that cost 3x the WCM but would be giving far greater value. If it is likely to cost 60x as much then clearly it is a non-starter.

Apologies if I have put this in the wrong forum, couldnt see anywhere in biology where this was quite right... I often hear various permutations of the statement that every atom in your body is different after a period of x years. Is there an authoritative source for this? Secondly, surely there has to be a positive probability that some of the atoms in your body are the same after x years even if it is in acompletely different place...and a very small chance. Thirdly I am sure I read that after a certain age the body does produce any new brain cells, so presumably this means that for the 7 year rule to be true it must be somehow rebuilding the same cell? Thank you!

If the earth was to rotate over say a period of 25 hours what would the impact be on night time and daytime temperatures? Would the relationship be linear, eg a 2 hour increase in rotation time would increase peak day time temperature on average by twice as much as a 1 hour increase?