# How old are the particles in my body?

1. Dec 2, 2012

### Warp

I'm not sure which group this question really belongs to, so "general physics" sounds like a safe bet.

This question was prompted by having listened to Neil deGrasse Tyson's more philosophical views about our nature and our connection to the universe, which are quite insightful.

Most of the larger molecules in my body are probably relatively recent (as living organisms build and break things like protein chains all the time.) Many of the simpler molecules, such as water, are probably much, much older (although I do not know all that much about the formation of such molecules.) Some might be quite recent, but some may be really old.

The atoms in my body are probably really, really old. Most of the heavier elements probably formed in the star or stars that were the ancestor(s) of our solar system, some may be even older than that. (If I have understood correctly, it's estimated that our sun is a third-generation star, meaning that it formed from the remnants of stars, which themselves formed from the remnants of the first stars in our universe.) It might be possible that some of the simpler atoms in my body were actually produced by the first-generation stars of our universe, so they are really, really old.

But how about the individual particles in my body? The protons, electrons and neutrons? Are they as old as the universe itself? Did they form in the first moments of the Big Bang? (Can such particles form afterwards?)

In other words, how old are the protons, electrons and neutrons (and possibly other particles) in my body?

2. Dec 2, 2012

### Staff: Mentor

It depends on your definition of "the [particle]".

As seen by quantum field theory, every interaction destroys a particle and produces a new one instead - as those interactions occur extremely often, no particle would be older than a picosecond.
In a more classical view, protons, electrons and neutrons stay the same until they are annihilated, decay or transform into other particles in a different way. This is quite rare outside of stars, so most particles were still present when our solar system formed about 5 billion years ago. Stars mainly convert protons plus electrons to neutrons (bound in nuclei) and do not produce electrons and protons, so those can be even older and most come from the big bang 13.7 billion years ago. Neutrons are "younger", as they mainly formed in stars afterwards. The same is true for most of the atoms in your body (apart from hydrogen and traces of helium).

Water molecules exchange hydrogen atoms all the time, Wikipedia suggest ~10 hours as timescale with a german paper as source. And even if you neglect that, water is an essential part in many biological processes.

3. Dec 2, 2012

### sophiecentaur

That's the most interesting thing I've learned today. (Even more interesting than the contents of the Leveson Report lol). Presumably that refers to the liquid state. That timescale is staggering - it's more along the lines of the conduction electrons in a metal than I could ever have imagined.
Shame that the paper's in German. I can ask the way to the station and get a beer with my German but little more. tschüß!

4. Dec 2, 2012

### Crazymechanic

Sorry for a little offtopic but this thread got me wondering if only a proton could learn to speak and tell his journey through space and time since the very beginning or close to that imagine what a bestseller it would be. HAH. (sweet dreams)
Also many questions would vanish.

5. Dec 2, 2012

### sophiecentaur

There would be many chapters with nothing much in! You would need a lot of editing, I think. How many different ways are there of saying "I met a photon"?

6. Dec 2, 2012

### micromass

Ah, but it could be a love story about him meeting a photon, falling in love, chasing her but not capable of catching up and then him decaying with a broken heart. Could be a nice story

7. Dec 3, 2012

### sophiecentaur

Photons. Seen one, seen 'em all.

8. Dec 3, 2012

### Crazymechanic

hahahah micromass. :D
just don't forget to put some werewolves in your love story:D

9. Dec 3, 2012

### Zarqon

But this one had such a nice frequency! Very well defined phase, and just the right amount of orbital angular momentum.

10. Dec 3, 2012

### Staff: Mentor

Probably (the study was done at 25°C or about 298K).

This allows to determine the coefficients kA and kD in the reaction $H^+ + OH^- \rightleftharpoons H_2O$.
$k_D=2.6 \cdot 10^{-5} \frac{1}{s}$ or $\frac{1}{k_D}=38500s$.