ask a physicist

[freyar]

That is, it pulls a notion that an initial frame of reference is a distinguished frame, and that physical properties such as the rate of passage of time (as measured by common physical processes, say, decay rates) will be measured as the same thing for different observers in the same initial frame, and similarly, that distances can be reliably measured (say, as a count of wavelengths of light as emitted, again, by common physical processes), and will yield a consistent result by different observers, and that these measurements will be stable over time.

The fact that inertial frames have a special name means they are distinguished! But the second part of your sentence is the content of the assumption. That's not something additional --- it's exactly what the postulate is saying.

Then, the notion of an idealized clock must be presented as physically meaningful, even if no actual ideal clock can be made. And, it turns out that certain physical processes can be used to make very accurate clocks. As well, one must demonstrate that if a number of idealized clocks may be created, they will be shown to record the passage of time uniformly, so that any irregularities must be shared by the clocks and by the observer.

I think you're getting a bit confused or hung up on something. An idealized clock is one without irregularities. It is a perfect clock. This is really not special to relativity but is in fact how physics is done. We think of perfect systems, stripped of worries about experimental noise, etc, etc. Theoretical physics is like what the world is in our imagination; experimental physics is about making measurements as close to that idealized imagination as possible.

It must also be shown that an idealized clock can be transported to various locations and remain accurate. (Knowing the results of the experiment, we will know that the clocks will show slightly different times after they are transported, but, they will still show the same rate of passage.)

Just transport them infinitely slowly. We're just doing this in our minds, so we can take an infinite amount of time to set things up.

 

[AbdulAlhazred]

So - the laws are all the same in our neighborhood. And in our galaxy. If there's some place in our sight that's substantially different, we should be able to see the difference when we look out into space. But we don't. So, the observable universe seems to have the same laws.

That's not enough for you? Wow. Tough crowd.

There's another thing even beyond this, Noether's Theorum. Much of our modern understanding of physics was built upon this theorum, which equates symmetries and conservation laws. By this means we know that either we've just by pure luck built most of modern high energy physics (too unlikely to even seriously consider) OR the laws of nature are the same in every inertial frame of reference, everywhere in space and time, and symmetric with respect to any rotation. Its really about as close to an iron-clad argument as you can get in physics.

 

[CaptainGemini]

What impact would it have on our understanding and study of physics if it turned out that Unified Field Theory is flat-out impossible and the universe exists as a series of interactions between different sets of physics?

 

[CaptainGemini]

There's another thing even beyond this, Noether's Theorum. Much of our modern understanding of physics was built upon this theorum, which equates symmetries and conservation laws. By this means we know that either we've just by pure luck built most of modern high energy physics (too unlikely to even seriously consider) OR the laws of nature are the same in every inertial frame of reference, everywhere in space and time, and symmetric with respect to any rotation. Its really about as close to an iron-clad argument as you can get in physics.

Please excuse the double post.

Here's where it gets complicated: We don't know how big the universe is simply because it's beyond our capacity to observe, but we know of around 91 billion light years.

Using the standard theory that the universe is speeding up as it expands, started at the speed of light, and has been expanding for fifteen billion years... At current, we cannot even observe one percent of one percent of the universe. An infinitesimal fraction of the universe's size could easily have a radius of three hundred billion light years. Even if only 1% of the universe obeyed the laws of physics as observable from Earth, you're still talking about an amount of space that we will likely never explore beyond at any point before the heat death of the universe. And that's even accounting for Star Trek-like FTL.

So, even if Noether's Theorum is wrong, we'll likely never know.

 

[freyar]

What impact would it have on our understanding and study of physics if it turned out that Unified Field Theory is flat-out impossible and the universe exists as a series of interactions between different sets of physics?

When you say "a series of interactions between different sets of physics," do you mean distinct forces, like the strong and electroweak forces as distinct forces in the Standard Model? I'd like to understand the question a bit better. My instinct is to say that it probably wouldn't have much impact in a practical sense, but I'd like to make sure I understand the question first.

 

[CaptainGemini]

When you say "a series of interactions between different sets of physics," do you mean distinct forces, like the strong and electroweak forces as distinct forces in the Standard Model? I'd like to understand the question a bit better. My instinct is to say that it probably wouldn't have much impact in a practical sense, but I'd like to make sure I understand the question first.

The idea that there's not one set of laws of physics, but multiple sets and that it is the interaction between them which causes the universe to exist. Kinda... Not a unified field, but multiple fields that don't necessarily get along.

 

[AbdulAlhazred]

The idea that there's not one set of laws of physics, but multiple sets and that it is the interaction between them which causes the universe to exist. Kinda... Not a unified field, but multiple fields that don't necessarily get along.

But there must be a set of principles which governs there mutual interactions, or there would be what, randomness? This set of principles then IS your laws of physics. Conceptually there either IS a set of laws, things happen consistently the same way all the time and each possible part of the whole universe must relate to each other part by some such consistent rule, or there isn't. There's really no halfway, is there?

 

[CaptainGemini]

But there must be a set of principles which governs there mutual interactions, or there would be what, randomness? This set of principles then IS your laws of physics. Conceptually there either IS a set of laws, things happen consistently the same way all the time and each possible part of the whole universe must relate to each other part by some such consistent rule, or there isn't. There's really no halfway, is there?

Conceptually, if you know both an object's velocity and direction of travel, you can derive its location at all times. But it's not actually true of all particles.

Just because it doesn't make any logical sense to us as we understand physics now does not preclude its capacity for existence. It merely demonstrates the limits of our capacity to understand existence with current knowledge. A halfway point that produces consistent results most of the time out of pure randomness is perfectly possible. It would also produce results that are completely unexpected, but might not be observable from Earth at this time due to current technological limitations. It might even explain the Sol System's quirks.

However, I was not suggesting the universe operates that way. I was asking how it would affect our understanding and study of physics.

 

[freyar]

Well, I'm still having trouble following the set-up. But, basically, if there is not any set of laws at all (ie, nothing we can understand), like if everything is at the whim of some set of battling D&D deities, then we just can't really do science. But that's an extreme case. Quantum physics has laws, but they are probabilistic and not deterministic, so we try to understand the aggregate statistical behavior of systems. Or we could talk about the laws of physics changing in some well-defined way across the universe --- there are people looking for variations of the strength of the fundamental electric charge over the history of the universe, for example. So I guess it depends on how extreme you mean.

 

[AbdulAlhazred]

Well, I'm still having trouble following the set-up. But, basically, if there is not any set of laws at all (ie, nothing we can understand), like if everything is at the whim of some set of battling D&D deities, then we just can't really do science. But that's an extreme case. Quantum physics has laws, but they are probabilistic and not deterministic, so we try to understand the aggregate statistical behavior of systems. Or we could talk about the laws of physics changing in some well-defined way across the universe --- there are people looking for variations of the strength of the fundamental electric charge over the history of the universe, for example. So I guess it depends on how extreme you mean.

Right, when [MENTION=6801122]CaptainGemini[/MENTION] suggests for instance that "A halfway point that produces consistent results most of the time out of pure randomness is perfectly possible. It would also produce results that are completely unexpected, but might not be observable from Earth at this time due to current technological limitations." then you'd simply have to explain why we consistently "don't see" this "pure randomness" in our part of the universe. If it is totally hidden then what we see is actually consistent, and we should be able to describe that consistency, and thus there ARE then laws of physics, because that's ALL that laws of physics ARE, consistent descriptions of how we observe things to behave, they can be naught else!

I think the point about Noether's Theorum wasn't really quite made either. It isn't something that may or may not be true. Noether's Theorum isn't a scientific result, it is a logical construct, it doesn't stand or fall, any more than the Pythagorean Theorum stands or falls. It is simply a truth. Furthermore we have a great deal of evidence that universal conservation laws and their equivalent symmetries exist because we observed conservation laws in action and then we derived symmetries from them. These symmetries were then used to derive further theories in physics which then matched observation, and this has happened MANY times. So either the observed conservation laws actually are really logically consistent and observed everywhere in our universe, or else most all of modern physics was discovered by random chance using a totally flawed process and we just got INCREDIBLY lucky.

This for instance is why we can with essentially 100% certainty rule out things like reactionless drives which violate Conservation of Momentum. If they exist, and Conservation of Momentum IS violated, ever, anywhere in the Universe, then all of our modern theories of physics are just blind luck, which we can state could only by true by chance at a level so unlikely that it is equivalent to zero. Now, maybe its possible to argue about what "anywhere in the Universe" exactly means, could it be that these things can be violated in some area of space which is causally disconnected from us (IE beyond our light cone and thus will never interact with us again for all time, and may have been causally disconnected since the start of inflation). I don't think we really know the answer to THAT, but is it even a meaningful question since we can never answer it, even in principle?