General Physics Thread

There are some secondary forces to rule out, but basically, the drone will remain in the same rotation as the earth, so no.

Thoughts on de Broglie-Bohm theory (http://plato.stanford.edu/entries/qm-bohm/)? If it "accounts for all of the phenomena governed by nonrelativistic quantum mechanics," then how can we tell whether it or standard QM is correct?

Can someone explain how imaginary time works in Layman's terms?

Well, I couldn't quite understand the specifics under the examples on wikipedia, but my interpretation of the first paragraph is that they don't mean anything on their own, but the quantities that result from their substitution have a physical significance. Like when you expand a real-valued function f(x) in terms of complex coefficients (like so◊), the exponent term refers to an individual wave, and the coefficients only give you the contribution of every wave. As such, a complex value of contribution has no physical significance, but the end result of using complex contributions results in a real quantity (obviously, by construction).

Of course, I am talking out of my ass right now, so if I'm wrong about it please correct me pronto since I'm interested too.

If I knew how I know everything I know, I'd only be able to know half as much because my brain would be clogged up with where I know it from

I'm guessing that imaginary time is that thing that they use to get around division by zero problems in trying to model black hole event horizons.

The description on wikipedia is somewhat off. They are missing the point that the imaginary plane is not the cartesian plane. You can use the latter to model the former, but clear differences emerge when you look at transformations. For example, if you multiply two complex numbers together, the angles of the numbers sum together, and the magnitude multiplies.

edited 20th Oct '16 3:31:29 PM by war877

It is important to remember that time is a vectorial quantity, i.e it has a direction. An imaginary time moves at a right angle to the normal flow of time, is how I've seen it described.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

How exactly does that work? Time moves from past to present, so it only has one direction. Stephen Hawking describes imaginary time as time acting like a spatial dimension, so it doesn't have a boundary, thus no beginning, which is also suppose to be the answer for "What the Universe is like before the Big Bang, where time as we know it doesn't exist?" How would an object look if observed by someone in real time? (I'm not a physicist or mathematician in any way, only asking because a Sci-Fi book I was reading mentioned it and basically regurgitated Stephen Hawking's word to explain it)

We are talking about mathematical scenarios, they most definitively are not limited to a forward movement. If you are looking backwards in time, you may see a negative time distance.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

Sorry for not making it clear, but I was actually asking for the physical effects of imaginary time. The book I read had a character who experiences imaginary time instead of real time, but the author never actually describes things from said character's perspective. Artistic License is probably in play, but I was kinda curious of how said character views the world.

Everything looks like noodles, or beams of light being shot out from the big bang in all directions.

In all likelihood, imaginary time is a mathematical convenience. It cannot actually be experienced. When time bends sideways near black holes due to the force of their rotation, that is still real time.

Is it bizarre for my phone to get better GPS detection from within my car?

I noticed this playing Pokemon Go, actually: walking around my neighborhood meant absolutely nothing; my character simply stood stone still, until I walked close enough to a neighbor's house to piggyback on their wifi.

However, being inside my car gave me a 60% chance of being detected. What's up with that? Is my car acting as an antenna? Is that even a thing?

Say to the others who did not follow through You're still our brothers, and we will fight for you

Do your car have a built in GPS system? Because if that's the case then its not that big a surprise. Your phone would be piggybacking off the cars GPS

I doubt it. It was a 2002 Honda Accord that cost $2000 six years ago.

Say to the others who did not follow through You're still our brothers, and we will fight for you

I just watched the following video about black holes, and... well, I am now very confused. Just how accurate is this lecutre on the topic of what a black hole is? Because I cannot wrap my mind around what it's trying to say.

edited 18th Feb '17 10:06:06 AM by MarqFJA

Fiat iustitia, et pereat mundus.

Well, even today we are relying on theories and speculation to know what happens inside a black hole. Are there some specific questions?

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

I am not a physicist, but for me, he did not tell anything new actually. I did face-palm, when he said that gravity is not a force at all. Sure, gravitons have not been found yet and therefore you could say it is technically not a proper force in the standard model, but it was such a flat statement without explanation that I just rolled my eyes.

I am a simple man, I like stories therefore I dissect and discuss them.

Gravitons will not be found, ever. Most likely. I don't remember the name but one scientist quoted by Wikipedia said that even though physically possible, it is not feasible within the current laws of physics for gravitons to be detected.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

Well, to start with, the following came across as nonsensical to me, even while taking into account what I already know as a layman of quantum mechanics and black holes...

1. Anything that reaches the event horizon will appear, to outside observers, to be frozen at that spot, no matter how much time passes after that thing reached the event horizon. This is barely — if at all — alleviated by the later admission that the black hole's gravity redshifts photos so much that they reach wavelengths outside the visible spectrum. The most obvious problem: Once an object has passed the event horizon, sooner or later, the photons carrying the object's image will run out, because no photon could escape the event horizon.

2. "A black hole is not an object." That seemed to be part of the gist of the video, which is utter bullshit, because all black holes I know of result from objects with mass (typically old, giant-sized stars) collapsing under their own gravity into quantum-mechanical singularities. That collapsed mass has to somewhere within the event horizon.

edited 18th Feb '17 1:24:57 PM by MarqFJA

Fiat iustitia, et pereat mundus.

For all we know, the mass "behind" a black hole is in a parallel universe to which the black hole is a gateway to. That said, to my understanding you can indeed never see an object fall through the event horizon. Not sure how that works from a photon perspective.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

... Doesn't that, you know, violate physics? Because you're basically describing a wormhole, which by current understanding of quantum mechanics is flat out impossible.

Then again, Science Marches On happened on classical mechanics. Who's to say we won't make another revolutionary discovery that reveals that scenario to be possible?

Oh I have no objection to not being able to see when an object passes the event horizon; any photons reflected/emitted at the exact moment of passage will obviously be frozen in place, because they're fast enough to resist being pulled into the event horizon's inside but not fast enough to escape, unlike photons on the outside. My issue is with the nonsensical implication that there will be an infinite number of photons to deliver the image of the object at the very last moment before it reached the event horizon.

A photon is a particle (and the smallest unit of waves... I think. You know, the whole "wave-particle duality" thing.), despite having zero rest mass. Why shouldn't it behave like other particles?

edited 18th Feb '17 1:40:50 PM by MarqFJA

Fiat iustitia, et pereat mundus.

See, my impression is that as these photons are ever more redshifted, the amount of energy they carry approaches zero. And integrating this decaying power output over an infinite amount of time yields a finite energy.

I'd be interested in the properties of gravitons, actually. If they carry momentum, they'd be subject to gravity themselves and such "self interaction" of gauge bosons leads to odd effects - the strong force is mediated by such particles, and it's suspected that the reason why this force does not decay with distance is because of the self-interaction.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

This webpage seems to answer some of your questions. Quoting the relevant bit:

As the video itself points out, black holes are consistent in both anthropic and massless universes, at least within the purview of general relativity. So, Idk, weird stuff. Objects, that have mass, can enter the black hole and cease to be objects. Ceasing to be an object doesn't mean ceasing to exist. I think. I'm not a physicist.

I've heard the idea that our universe is merely one along others inside tight packed... extra-universal things, that from our perspective is the fabric of space-time, and black holes are... disturbances in those things that allow new universes to spring forth inside their own thing. It's like our universe is a bubble in a multi-universal foam, and trying to pop the bubble from the inside merely creates more bubbles.

These kind of ideas are mostly just out there unless we have an actual way to measure "what was before the Big Bang" or "what is out there besides the universe." Although "the universe" should encompass everything that is, not just, well, "our universe". Semantics.

If I recall correctly, the thing about being able to see objects entering a black hole for infinite time isn't about the number of photons. The idea is that the black hole bends the path of the photons leaving the object, and this bending causes the photons to take longer to reach the observer. As the object approaches closer and closer to the black hole, the path gets bent more and more, until finally it reaches the event horizon, where the effect is so huge that the photons take infinite time to reach us. So the photons, finite as they are, are distributed (for lack of a better word) in a way that the object can be seen approaching the black hole forever.

EDIT: Ignore this if this explanation was giving in the original video, which I didn't watch before posting this.

edited 18th Feb '17 9:50:39 PM by Elfhunter

If I knew how I know everything I know, I'd only be able to know half as much because my brain would be clogged up with where I know it from

That still requires that there's a similarly infinite number of photons reflected from the object to give us an infinite-duration image of said object from that last moment. If the photons were finite as they should be, then each photon taking longer to reach us than the previous one does would ultimately result in interruptions in the image as the increasingly larger gap between each pair of photons' arrivals becomes big enough to be noticeable by the human eye or recording device that is observing the whole thing. Eventually the interruptions become so big that we shouldn't even notice any images; AFAIU, human sight and current image-recording devices require much more than an instantaneous fraction of a second's worth of photons to actually perceive an image.

edited 19th Feb '17 3:13:23 AM by MarqFJA

Fiat iustitia, et pereat mundus.

The numbers of photons can be infinite, you know. There is no "law of conservation of photon number" as far as I know, and none of the other laws can be read this way. Besides, what is "a" photon here? A single wave packet?

edited 19th Feb '17 3:18:51 AM by SeptimusHeap

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman