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I calculated that I've spent just over a week airborne over the past 12 months covering a distance of about half a light second. Does this also mean that I've travelled half a second further into the future than if I'd remained at home, or is the maths more complicated?
Half a light second (150,000 km) over a week period (7 days) is an average speed of 248 m/s. If we assume you traveled more or less at the same speed throughout your journeys, then after a 7 day period (604,800 seconds) you have travelled 0.0000002 seconds into the future (a fifth of a microsecond). Peaks in speed might change the result a little because of the strong dependance between time dilation and speed but I think this is negligible here since your are still moving in the low speed regime.
I obtain a 0.2 seconds result when I subtract 3 zeros to the speed of light. Maybe there is the problem. 300.000 km/s is 300.000.000 m/s.
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Another unrelated question. When will hydrogen and helium become minority elements in the universe? Will it even happen at all?
That's a very interesting question and I doubt there's a simple answer. My bet is on the "Hydrogen will never be second rank in the chemical abundance of the universe" and here is why;
The chemical evolution of the Universe is driven by stellar nucleosynthesis or supernova nucleosynthesis, so star related processes (Big Bang nucleosynthesis finished a long time ago and we are going to ignore here us or aliens fusing Hydrogen like mad for billions of years across the Universe). So, the question is will the stars combust enought Hydrogen and produce so many heavy elements as to change the chemical abundance of the Universe
enought before the end of the stelliferous era?
This is the "astrophysics periodic table". You can see how the elements were created. The vast majority of them depend on the existence of stars.
The stelliferous era is limited by the first stars of the Universe, 155 Mry after the Big Bang, and the last star some 1014
years from now (100.000 eons from now). This means that we are at the beggining of the era at 1/10.000th of the entire period (if the stelliferous era were as long as a human life of 100 years, then we would be 3 days and 16 hours old). This might mean that there is plenty of time to fuse the vast ammounts of Hydrogen we found in the Universe.
After the Big Bang 75% of all the ordinary matter was Hydrogen (by mass, but by number it was 95%). After 13.8 Gyrs of evolution we have reached a situation were 73.9% is Hydrogen. So, 100.000 eons will suffice to get to the 50%? Let's think a bit about it. That 1.1% decrease in Hydrogen over the entire history of the Universe was performed almost entirely in the first hundred million years when the large primordial stars burned Hydrogen at furious speeds. Also the star formation rate has dropped at least an order of magnitude, since the first hundred million years and the universe is very quiet now in comparison. So the drop in Hydrogen abundance is not constant, its slowing down.
Now remember that stars are not perfect fusion engines. Fusion only happens at the core, so 10% of the mass of the star is subject to fusion. But even then not all that 10% would be fused since the core is intoxicated with heavy elements that sink into the heart of the star. Currently stars are almost entirely made of Hydrogen but the majority of this Hydrogen will last for billions of years and will survive after the death of the star itself (refueling another new-born star perhaps). Also think about all the Hydrogen lost as a diluted substance by stellar wind (protons are ionized Hydrogen atoms). Stellar winds will have a hard time to coalesce into a cloud and collapse into an other Hydrogen fusing star, those atoms can only hope to be fused if their orbit across the galaxy intersect a star froming region or are pulled by a dense object. In fact the interstellar medium of our galaxy is full of Hydrogen that has yet to be fused (most of it comes from the outer shells of exploded stars). At least 5 billion solar masses of Hydrogen (5% of the mass of the galaxy) is still lurking in the galaxy as interstellar medium (a galaxy that has been here for 11 billion years and hasn't been able to depleate all that hydrogen, try to think about all the hydrogen still present in all the stars that wont get fused any time soon).
But yeah, one could argue that in the end, after 100.000 eons our galaxy (and all the galaxies) would be able to deplete all the hydrogen inside them, slowly.
But what about outside the galaxies? Look at the Smith Cloud
for example, it is a 9.800 light year sized beast containing 1 million solar masses of Hydrogen that we have been able to detect only because it is getting warm while colliding with our galaxy. Take a look to Hanny's Voorpwerp
a huge hydrogen cloud, extending hundreds of thousands of light years and boasting a total mass amounting to five billion times that of the Sun. We have seen that cloud only because a nearby galaxy went into an active period and relativistic jets shooting from the central black hole probably brightened the cloud.
Clouds like this or larger might be here and there close and far to our galaxy and others, just floating in the darkness of intergalactic space since the beggining of the universe, filled with pristine Hydrogen and unable to collapse on themselves to form stars and fuse that Hydrogen because of the low densities involved and the scarce interactions with other objects.
Will stars deplete the majority of Hydrogen from our galaxy? Maybe. Do galaxies will absorb the majority of intergalactic hydrogen still present? I have a serious doubt. Inside galactic clusters between 80% and 95% of matter
is located in the intracluster medium instead of the galaxies themselves (according to Wikipedia
) and the chemical evolution of that sparse matter has been small so that is almost all Hydrogen and Helium. There are not only "clouds" (as Smith's cloud or Hanny's Voorpwerp) in intergalactic space but there is also the so called warm–hot intergalactic medium
, a ethereal gas/plasma made basically of Hydrogen atoms and nucleai, which accounts for the 40% to 50% of the entire mass
of ordinary matter in the Universe. A fraction of this gas might be pulled by galactic clusters and galaxies fuelling partially some new stars in the next trillion years, but the vast majority of it will survive without collapsing to form stars in the huge cosmological voids
As matter in the universe coalesces in specific regions of space (galaxies become point-like gravitational atractors in the cosmological context) the intergalactic voids open and get larger (they even start fusing toghether), and if the hydrogen is not quickly pulled by galaxies the residuals are going to be harder and harder to pull from the voids. Newton's shell theorem
(the fact that inside a hollow spherical shell there is no net gravitational attraction to any of the walls) and the Cosmological Principle
(the fact that the Universe at this scale is more or less homogeneous in the distribution of matter) imply that the intergalactic medium (and particularly the gas inside intergalactic voids) is very difficult to suck. This fact combined with the expansion of the Universe will probably (in my opinion) make vast ammounts of Hydrogen unaccesible for galaxies and star formation would cease even if astronomical amounts of Hydrogen would still be present in the darkness of the Universe.
I don't think Hydrogen will ever leave the throne of the most abundant element in the Universe. But I could be wrong.