Did General Relativity and Quantum Physics *have * to be part of our universe?
That is, is it feasible for a universe to exist that follows Newtonian Physics at all speeds, and doesn’t behave “weirdly” at the quantum level, and yet still behaves on a macroscopic level like our universe?
For example, the speed of light is fixed in all reference frames and nothing can travel faster than c. Did this have to be the case?
If there was a universe with no maximum speed limit on anything, and no time dilation and no spacetime warping, and no quantum probabilistic properties, could that universe exist and have properties on our everyday-life-level that are the same as what we experience today in our everyday life?
Or is it the case that if any of the above was different, there is no way of getting a universe anywhere close to our current one (at least from a day-to-day-experience point of view)?
Before QM was formulated, physicists were at a loss to explain how the atom could be stable. It was first thought that electrons swam in a sea of positive charge, but Rutherford showed that the postive charge was concentrated in a very small region (ie, the nucleus). An electron orbiting the nucleus like a planet would constantly be losing energy (an eccelerating charge emitts electomagnetic energy). Such an atom would decay in about 1/(10^23) seconds.
QM solves this problem nicely. So, no, the universe could not exist with electrons and protons and neutrons if they behaved classically.
Also, the sun’s energy is the product of nuclear fusion. Two hydrogen atoms fuse to form helium + energy. The energy released is determined by the difference in mass between the 2 hydrogen atoms and the 1 helium atom. E=mc^2. Get rid of that, and the sun would not be the same energy source that it is.
One reason quantum mechanics turned out to be “necessary” is that a classical universe requires an ** infinite** amount of information! If space and time are unlimitedly divisible, then just to specify the relative location and velocity of two particles would mean giving three location values and three velocity values (for x, y & z in space) to an infinite degree of precision: 4. 4392543980487…(forever) centimeters, and so forth.
I don’t think there’s necessarily anything “weird” about the universe. It is what it is. It’s just that we’re trying to understand something that we’re really not equipped to deal with. Humans are designed to survive by finding food and shelter. It’s just not in our nature to understand how subatomic particles interact. That’s why we’re having such a hard time with it, and why it seems “weird” to us.
The universe is so. It is how it is, not some other way. GR and QM are the descriptions formulated by these incredible neural networks in our skulls which are our attempts at encoding the universe how it is, rather than how it is not.
The universe (or, at least, this region of the universe having 3 dimensions of space, 1 dimension of time and an incredibly finely balanced ratio of the strength of gravity vs. electrostatic repulsion) could almost certainly not have spawned the complex structures (eg. stars, liquid water) required for life had it been even slightly different. The differences manifested by no GR or QM would be far in excess of those required to leave the universe a dull, lifeless homogeny.
Well, the fact that something can be in two states at the same time, and then collapses to one of the states just because someone observes it: *that * is weird.
In any case, even if we stop calling it weird, the question remains: can there exist a universe that does not have a limit for the speed of light, where spacetime is not warped by the presence of mass, etc, and yet still has all the everyday characteristics we are used to?
Perhaps I’m being denser than uranium today but what would prevent a universe from being all those things? It wouldn’t be our universe, for sure, but why not someone elses?
The universe cannot be such that the evolution of complex life-forms is impossible, since we’re here. The condition for complex life is so specific that the differences caused by no GR or QM would surely result in a universe without enough long-lived structure: “someone else” could simply not develop in a universe made solely of hydrogen, or one which never cooled below 1000K.
I understand this. I’m just asking if we can construct a theoretical universe that does not obey special or general relativity, or quantum mechanics, and yet still appears to us, in our everyday experiences, identical to the one we live in today.
This is true given the current laws of physics (*with * GR, QM, etc).
What if we had different laws? Not necessarily for describing our current universe (which *does * obey GR and QM), but for allowing the existence of a universe with an everyday experience identical to ours.
I’m saying that science has discovered that GR and QM describe *our * universe, but is it the case that they are necessary in *any * universe with our everyday experiences?
This is merely a conjecture on your part. What *specifically * would break down?
How would the world be different if things could travel faster than 3x10^6 m/s ?
How would the world be different if clocks did not slow down when moving very fast?
Why are these things necessary for a universe to provide us with the everyday experience we see today?
An example: if I keep hearing some noises coming from my neighbor’s house, I can study the issue and find out that he has the weird habit of recording his cat and playing back at a very slow RPM. But, just because my neighbor turned out to be weird, does not mean that the explanation could not have been something else. That is, there are numerous other scenarios under which I would have experienced the same noises coming from my neighbor’s house.
So, just because GR and QM ended up being how our universe works, does not necessarily imply that our universe *had * to be this way for us to experience the things we do everyday. But, it is possible that, due to some fundamental reasons, a universe without GR and QM can never provide us with the everyday experience that we see today. If so, what are these fundamental reasons, and why/how do things break down without GR and/or QM?
I’m really rather unsure how to answer here. What if I simply modelled the universe as “The sun shines and then the stars come out and the birds sing and I go to my mum’s for tea and we have ice cream and it is very nice”? Clearly, we must impart a level of sophistication to our model.
And that’s where, ultimately, we need GR and QM. Why does the sun shine and the stars come out? Because universal gravitation draws together those boring gas clouds under the laws of GR. Under the laws of QM, that thing gets hotter, eventually fusing hydrogen into helium and releasing energy. Gravity (GR) and nuclear fusion (QM) compete until, if the star is big enough, a supernova blows the whole lot around the galaxy.
So, if GR and QM are “not the case”, what do we do in our model? Do we simply say, “oh well, gravity and fusion make the sun shine”? How? You are asking me to explain a feature fundamental to the universe without actually explaining it.
(Bear with me on this one, since I’m not a physicist, as can plainly be seen :))
Let’s take gravity.
Why do two masses attract each other? From what I know, GR says that the two masses warp spacetime around them, and each mass “falls” into the curvature created by the other mass.
But, why do masses have to follow the curavture of spacetime? What force compells them to do so?
It seems that we have taken one statement “masses attract each other”, and converted it into another statement, “masses follow the curvatures of spacetime”, but we don’t really know why the latter is true, so knowing the latter doesn’t seem to have given us “the truth”.
Also, let’s take the statement “two opposite charges attract each other”. Does modern physics know what “charge” really is (beyond “it’s a property of matter”), and what the *exact * mechanism is of how charges attract each other?
So, if we have a physical theory that involves the statements “masses attract each other using this relationship” and “opposite charges attract each other using this relationship”, I would be content with that theory (today’s theories only go slightly deper in giving us more fundamental reasons)
So, I can see how we can have a sun whose gases are held together using some theory of gravity, but not necessarily needing GR.
I think the point here is that without the relationships and reactions described with QM and GR, we’d have no gravity. It’s not as if they’re just a nifty add-on feature to normal-everyday gravity.
I could imagine a universe where gravity worked by the principle of lime jell-o, but that’s pretty non-sensical.
What you seem to be asking is, “explain a logical way for us to have gravity (or whatever) without having gravity.”
Take John Mace’s example, for example. There’s one reason why, yes, we do need the principles which GR and QM describe. One could say, “but let’s say that an atom could be stable without quantum principles,” but it isn’t.
Pretty much, yes. Electromagnetic forces are carried by elementary particles called bosons.
Firs things second:
Fitting gravity into the Standard Model is the next step. Unfortunately, the Higgs Boson (which gives particles their mass) has not yet been observed, and unifying gravity with quantum mechanics is proving a mite difficult.
However, that these haven’t yet been unified is irrelevant here. They each describe the exact mechanisms of the parts they each play in eg. stellar fusion perfectly in their own way. You seem to be asking “could Newton be right but Einstein be wrong?”. Of course he could, but you’d then have a whole raft of things which Einstein can explain but Newton can’t.
OK, so why is difficult to envision a universe where gravitational forces are carried by some other elementary particles, without need for a warped spacetime?