1

General Science / Re: How much of me is original?

« on: 30/06/2022 18:30:24 »

(not teeth - they all fell out and were replaced when you were a child!)

The replacements may have already been in place, but it's probably beside the point.

I'm not saying this is an accurate mechanism to answer the question but it does give some indication.
In a typical year you can expect to eat something like 1000 Kg of food. That's about 7 times your weight.
The stuff food is made from isn't very different from the stuff you are made from.
So each year your body takes in 7 times its mass in "stuff".

If that were properly mixed then only 1/7 of you would be still there at the end of the first year.
So it's 1 in 49 after 2 years and by the time you are 65 it's pretty close to bugger all.

Obviously some bits are better mixed than others.
The chip in my front tooth that I have been carrying round since school is still there- more like 45 years than 65, but the point remains.
Most of that stuff is pretty much fixed. Skeletal bone is turned over much faster than that, but still pretty slowly.
My skeleton is something like 10Kg
It contains something like 1400 grams of Calcium
"The calcium content of bone at maturity is approximately 1,200 g in women and 1,400 g in men"
from
https://www.ncbi.nlm.nih.gov/books/NBK56060/
and it turns over about 0.5 grams per day
https://www.medscape.com/answers/241893-20078/how-much-calcium-turnover-occurs-normally-each-day
so that's about 180 grams per year or (very roughly) the whole lot gets rebuilt every 7 or 8 years.
Some bits deep in the middle might date back to when I was a teenager.
At best, very little of it will be original.
"At full-term birth, the human infant has accrued about 26 to 30 g of calcium, most of which is in the skeleton."

Just a thought; if we are what we eat, why are we not "new and improved"?

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General Science / Re: How much of me is original?

« on: 30/06/2022 17:19:41 »

So apart from bits of brain  (not teeth - they all fell out and were replaced when you were a child!) and I think a few nerves, what is "you". Is the lump of stuff that people call by your name, really the same person as on your birth or marriage certificate? If not, how can anyone be held liable for past actions? Is a 10-year passport really a  valid document?

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General Science / Re: How much of me is original?

« on: 30/06/2022 16:36:00 »

Teeth are all I believe that is not replaced, they are used as a locator for isotopes in the water in the region that you grew up in.

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General Science / Re: How much of me is original?

« on: 29/06/2022 22:53:11 »

Some cells are not replaced during your lifetime. This applies to the lens of your eye, and brain cells.
- Most parts of the cell are generated from instructions in the DNA, using new raw materials from your diet
- But if the cell does not divide after birth (eg brain), it can continue to use the same DNA with which you were born
- Some parts of the brain do generate new cells (eg hippocampus), but this does not apply to most of the brain
- There will be spot repairs to DNA when it is damaged by natural radioactivity or metabolic stress, and these repairs would be made from "new" atoms in your diet.

I understand that some of these DNA ages were determined by measuring the radioactive content of DNA from different tissues. The isotopic mix in the diet changed noticeably in the years that atmospheric nuclear testing was underway.
https://www.sciencefocus.com/the-human-body/what-cells-in-the-human-body-live-the-longest/

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General Science / Re: How much of me is original?

« on: 29/06/2022 22:18:46 »

Every cell split, only half the dna atoms are 'original', and the other half (both cells) are made from atoms from the environment.

All in all, probably under 0.1% (probably well under) of your birth atoms are still in you.
You birth atoms are also not original since you did an awful lot of growing before you were born.

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General Science / Re: How much of me is original?

« on: 29/06/2022 22:13:57 »

I know my dna remains the same

I wouldn’t be so sure about that. DNA does mutate as it passes from cell to cell and we age.

For instance, will any of the original heart I was born with remain with me now?

I would say not a lot, if any, of the original cells. Usual quoted cell replacement is between 7 & 10 years, but can be shorter for important organs.

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Physics, Astronomy & Cosmology / Re: Cosmic inflation, before or after the big bang?

« on: 26/11/2021 13:46:30 »

'is it now agreed that cosmic inflation occurred before the big bang?

No, of course not.

Also is there a reliable source of information I could access regarding this point?

https://wmap.gsfc.nasa.gov/universe/bb_cosmo_infl.html

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Physics, Astronomy & Cosmology / Re: Cosmic inflation, before or after the big bang?

« on: 25/11/2021 14:14:55 »

Is it now agreed that cosmic inflation occurred before the big bang and if so does it make a big difference to our original understanding that inflation occurred after the big bang?

From what I can tell, there is but the one mainstream model which is not ambiguous on the ordering of the epochs. The only difference is semantic: which exact moment in time (before inflation, and how much before, or after it) to assign the label 'Big Bang'.
It is legitimately questionable since time as we know it, measured in seconds and such, isn't really a meaningful measure when describing the inflation epoch. Hence the reluctance to assign 'time zero' to the point at which things were most compact.

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Physics, Astronomy & Cosmology / Re: Is it possible to recreate a black hole?

« on: 24/11/2021 20:33:10 »

Is it possible to recreate a black hole?

This question implies that a black hole previously existed, and you want to recreate it.
- Unfortunately, for stellar-mass black holes, they persist for an extremely long time.
-They evaporate via Hawking Radiation, and are expected to last about 10⁶⁴ years.
See: https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_evaporation

There is a possibility that micro-black holes could be formed in extreme energy conditions, such as the Big Bang, and these could last to today, in which case they would very tiny, and would explode in a blaze of gamma rays and subatomic particles.
- It is theoretically possible that some future super collider (far more powerful than the LHC) could create micro black holes, which would promptly evaporate. The LHC has been watching for these events, but it is regarded as a faint hope (the energies required are far too high).

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Physics, Astronomy & Cosmology / Re: How long does a gravitational wave last?

« on: 24/11/2021 08:46:33 »

@Harri
I’ve changed the title of your question from gravity wave to gravitational wave.
A gravity wave is one that uses gravity as the returning force eg water waves.

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Physics, Astronomy & Cosmology / Re: How long does a gravitational wave last?

« on: 24/11/2021 08:38:39 »

does such a massive event only produce a wave/s capable of being observed for a very short length of time?

It takes millions of years for two black holes to merge, and they radiate gravitational waves all that time. However:
- The frequency is too low for LIGO to detect
- The power level is too low for LIGO to detect
- A proposed space-based gravitational wave detector would be able to measure much lower frequencies, and so may be able to detect hundreds of pairs, all slowly getting closer to each other, months before they move into the frequency range detectable by LIGO.
See: https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna

From another angle, some of the observed events are billions of light-years away. So any observers with similar equipment to ours would have been able to detect them long ago.  See the list here (1 MegaParsec=Mpc = 3.2 Million light-years).
https://en.wikipedia.org/wiki/List_of_gravitational_wave_observations

is the total  energy  level  on each concentric ring of the sphere the same no matter the distance from the source measurements are made?

If you add up the energy in each expanding sphere, it will stay the same, no matter how far you travel.
- Apart from some loss due to refraction from black holes, etc
- Which would not be much, because a stellar-mass black hole is perhaps 10km across, while the wavelength of gravitational waves is 1,000 km or more. A wave is not much affected by anything smaller than 1/4 wavelength. But a black hole in the center of a galaxy would have more of an effect on the higher-frequency gravitational waves.

always getting weaker by distance per the inverse square law.

As I understand it, our current generation of gravitational wave detectors do not measure the energy of the gravitational wave directly, but measure the strain of the spacetime distortions. The energy is proportional to the square of the strain.

This means, of all the methods used by astronomers for exploring the universe, this one does not suffer from the inverse-square law, but degrades as an inverse law.
- If you increased the area of an optical telescope by a factor of 4, you would be able to see twice as far, and explore a volume 8 times larger (inverse square law).
- If you increased the sensitivity of a gravitational wave detector by a factor of 4, you could see 4 times as far, and explore a volume 64 times larger (inverse law).

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Physics, Astronomy & Cosmology / Re: How long does a gravitational wave last?

« on: 23/11/2021 15:59:29 »

LIGO has a frequency range to which it is sensitive, about 10 hz to 10k hz, no so different from the range of sound detectable by people. So if the massive objects orbit slower than a 5th of a second, LIGO isn't going to pick it up. Near the merger, the frequency rises very rapidly, resulting the characteristic 'chirp', after which the signal is no longer detectable.
It apparently takes under a second for an orbit to drop from a 5th of a second down to at least the photon-sphere, after which the wave signal fades away.


The waves do 'last forever' in the sense that they keep traveling past Earth out forever, always getting weaker by distance per the inverse square law.

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Physics, Astronomy & Cosmology / Re: A particle in 2 places at once?

« on: 03/11/2021 19:04:16 »

A particle, by definition , can only be in one place at any instant. Problem is that the more accurately you know where it is, the less accurately you know how fast it is travelling or where it will be next. That's simple continuum physics leading to Heisenberg's indeterminacy principle.

Not to be confused with the Schrodinger interpretation which states that eg for an electron, all we know is the probability density distribution of finding it anywhere.

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Physics, Astronomy & Cosmology / Re: A particle in 2 places at once?

« on: 01/11/2021 19:18:20 »

It is when I read that 'a particle' can be in two separate locations at once

Perhaps you are referring to the 2 slit experiments, where an electron passes through both slits?  This is not a particle being in 2 places at on time, this is a demonstration of the wave nature of an electron.  An electron is not a particle in the classical sense, so the 2 slit experiment does not say a particle is in 2 places at the same time.

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Physics, Astronomy & Cosmology / Re: A particle in 2 places at once?

« on: 31/10/2021 23:25:30 »

I often read that particles can be in two separate locations at once.

This has certainly never been demonstrated, and while not denying it, I am unaware of a quantum interpretation which goes to far as to assert this.

I’m not aware of one either. I think this is a misinterpretation of the solution to some wave equations where there is equal probability of 2 or even 4 solutions; that doesn’t mean those solutions exist simultaneously.

It is when I read that 'a particle' can be in two separate locations at once I wonder if the statement is true and if it is at all helpful to describe it as such when discussing superposition?

A cat being in superposition of dead and alive is not the same as saying it is both dead and alive. I think that's the disconnect not spelled out well in statements that word it otherwise.

Agreed, it’s a common misunderstanding of the Schrödinger’s thought experiment.

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Physics, Astronomy & Cosmology / Re: A particle in 2 places at once?

« on: 31/10/2021 17:08:36 »

I often read that particles can be in two separate locations at once.

This has certainly never been demonstrated, and while not denying it, I am unaware of a quantum interpretation which goes to far as to assert this.
So it sounds to me like poorly worded pop literature. I've no doubt that such statements are out there.
I might say that it is incoherent to talk about a particle being at a location (let alone more than one) at all. A particle is measured at a location, or it isn't. That's all we know for sure.

It is when I read that 'a particle' can be in two separate locations at once I wonder if the statement is true and if it is at all helpful to describe it as such when discussing superposition?

A cat being in superposition of dead and alive is not the same as saying it is both dead and alive. I think that's the disconnect not spelled out well in statements that word it otherwise.

How could one particle occupy two places in spacetime?

Spacetime is a different story. My hand is down. My hand is raised. Both these states are in spacetime, but in only one state at a particular time, where time is a chosen cross section of spacetime. That's the same as a highway 80 being in Chicago and New York at the same time. It's not a contradiction, it's just in those places at different locations along its length. A particle is similarly not a point (an event) in spacetime, but rather a worldline in spacetime. Being a line, it doesn't exist all in one place. This has nothing to do with superposition. It's a classic concept.

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Physics, Astronomy & Cosmology / Re: What if the universe really is infinite?

« on: 21/10/2021 23:05:54 »

Does the big bang theory cause a problem for the infinitely expanding universe theory?

The big bang theory is the infinitely expanding universe theory

Our universe is currently expanding

Careful. The space in our universe is expanding over time. 'The universe' is typically defined as all of (or sometimes the visible portion of) spacetime, and spacetime doesn't expand or otherwise change, so while wording it that way is common in pop articles, it is technically wrong.

my understanding is that a reduction of that expansion would bring us to the big bang.

That would be a big crunch, a sort of different thing that the big bang in reverse since the entropy would be so much higher. Our expansion doesn't look like it will ever slow let along reverse, so no crunch is anticipated.

But wouldn't that mean that the reduction would also have to be infinite?

The expansion isn't infinite, so neither need be the reduction. The expansion is currently at a non-infinite rate of 70 km/sec/mpc and might eventually settle on an exponential rate of around 57.  The size of space is posited as infinite, but you can expand that or reduce it by any finite figure and it's still infinite. Expansion/reduction works just the same (same finite measured rate) regardless of whether the size of space is finite or not.

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Physics, Astronomy & Cosmology / Re: What if the universe really is infinite?

« on: 21/10/2021 22:59:58 »

Does the big bang theory cause a problem for the infinitely expanding universe theory? Our universe is currently expanding and my understanding is that a reduction of that expansion would bring us to the big bang. But wouldn't that mean that the reduction would also have to be infinite?

(think my head just expanded   )

Well could you have it so that some of the universe did fall back on itself but some was just too far distant and "out of reach" so that it  continued its expansion "to infinity and beyond"   ?

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Physics, Astronomy & Cosmology / Re: What if the universe really is infinite?

« on: 20/10/2021 12:56:43 »

I know the idea of another 'me' out there in our universe is totally hypothetical and possibly not provable one way or another

Again: If
A) our universe is spatially infinite
B) You accept that effect can precede cause or that a cause can have effects at faster than light
C) The universe is everywhere in some state at a given time, however unknown or unmeasured

Only then does it logically follow that there must be arrangements of atoms identical to the arrangement of atoms that is you here. All that remains is:
D) do you consider that identical arrangement of atoms to be another 'you' which of course depends on your definition of identity.

I personally accept only premise A) and neither B nor C, and therefore if asked if these copies exist, I'd say no.
It depends significantly on your quantum interpretation of choice. There's a nice chart on wiki: https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Comparisons
The 3rd to last column is 'local dynamics' which is green if B) is false.
The 2nd to last column is 'counterfactual' which is green if C) is true. No valid interpretation can list both as green, as proven by Bell.  Only the bottom two interpretations meet the criteria above. Essentially Bohmian mechanics. If that's not your interpretation of choice (it certainly isn't mine), then these 'copies' don't exist.

do they need to take into consideration what happens to 'me'

I don't think this can be answered without a definition of what you consider 'me' to mean.

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Physics, Astronomy & Cosmology / Re: What if the universe really is infinite?

« on: 20/10/2021 10:11:14 »

But for those who have indicated the possibility of this being the case, have they or do they need to take into consideration what happens to 'me' and our universe before relativity, at the uncertain quantum level?

Not sure how relativity would come into it, but if you don’t know of their existence then it would be impossible to take into account what happens to them.
As @Halc says, you need to consider what you mean by identity ‘me vs otherme’. This has been explored to some extent in Star Trek and other sifi with respect to the transporter.