Klaynos

Yes, and potential to respond to give an idea of their approach speed. A few things have stopped me building a prototype. Waterproofing, it looking odd, not being convinced it'd actual capture the approaching cyclist, securing it in a semi stable way. Laser rangefinding might be better practically but i have the acoustic sensors and know how to use them...

I've been studying physics fulltime for more than 12 years. The list of things I don't understand is much much longer than the things I do. Even in the field I now work I have a spreadsheet of research projects we need to do to answer various questions.... It only ever gets longer not shorter.

I'm both a cyclist and pedestrian (and driver) depending on the weather. As a pedestrian if I know there's a cyclist approaching my response is to be more consistent unless I'm blocking the path then it's too look at the cyclist and clearly step out of their way. My use case would be to ensure consistency near cyclists and they sometimes go past rather quickly and pretty close which can make my jump with my headphones in... Like anything in this area it cannot replace considerate shared space users.

It's the same principle as laser distance sensors but cheaper. You send out a pulse of photons or sound (normally ultrasonic) it bounces off something and the time of flight gives you distance. If you do it twice in rapid succession you can work out if the object reflecting off of is approaching or moving away.

RFID isn't a great tech for this. Doesn't really have the range. I've considered a "cyclist approaching" warning system. Rucksack with rear facing acoustic distance sensors. If the sensors detect a rapidly reducing distance (cyclist approaching you add you're wedding along) then alert the user using a vibration motor. You might be able to do side detection with angled sensors. I've never thought about it long enough to work out whether it's actually feasible. For cars they're probably moving too fast relative to the pedestrian for it to work well. Pedestrians can change their motion very rapidly which makes collision avoidance much harder than say ships or planes where trajectory prediction is relatively easy. Car/pedestrian interactive can go from safe to fatal accident with little to no warning. Certainly not enough for a human to react. Collision avoidance on all cars would be best in my view. But then it'd need to be good. Drivers drive more safely with spikes in front of them rather then airbags. Really it's best to remove the human controller.

This is a philosophical discussion. Qm works as a good mathematical model for parts of the universe (its domain of applicability). The same can be said for classical mechanics etc...

I'm sorry this doesn't seem to make sense. Can you try again?

This is philosophy. You posted in physics. I'd suggest looking at the other threads on this in philosophy. Don't expect any firm answers either.

I think that's not a terribly accurate description of time in qm. But if we assume you're telling about tube appearing in the Heisenberg uncertainty principle then the same can said for space. More generally on uncertainty, every measurement has an associated uncertainty. Is everything an illusion?

The problem with this argument is that it can apply to pretty much every measurement technique that we have. Is space real? Is frequency real? Is intensity really? Etc... At some point you need to use a definition of real that makes sense. You've used physical again. Which given your previous definition time is trivially physical. Whether whatever you think is flowing is physical I dont think so. But you're using some unusual visualisation of how time works that doesn't seem consistent with science.

That's not a bad definition, it tends to be used by physicist as things which don't break the known bounds of physics, E.g. a photons rest frame is not physical.

It's a common theme on the forum. Virtual, imaginary, physical, real, theory, etc... If you don't get in early with s definition the thread can spiral. You can see here as soon as the OP gave his definition of physical it is trivial that time is consistent with it. Here then went on to change his definition but that's just sloppy.

I agree a clock and a tape measure are the same. Time and space are fundementally related. Whether they are things needs a good definition of "thing". Exactly why I got the op to define what he meant by physical earlier.

This applies equally well to space (with a few minor changes) so is space only an illusion? If time is an illusion I hope you don't have a job where you need to submit time sheets as you'd be fired pretty quickly.

I was using your definition of physical, which didn't include existence not velocity of flow. Could you define existence, what on earth a fire if time is (1 second per 1 second is pretty much meaningless). And perhaps not change the goalposts? You gave a definition how about sticking to it rather than deciding you don't like the answer your own definition have.

Then trivially, yes, time is physical. We have empirical measurements of it (clocks) and many equations in the physical sciences which include it. (On what are photons made of, they're fundemental, a photon is made of a photon. The same can be said for electrons etc...)

Newport would have been my second look. And given your reply I would have indeed pointed you towards piezo devices. Good luck and let us know how it goes. I love spectrometers. Just a shame I don't get to play with them anymore.

Ok, that's a reasonable sum. You should be able to get a decent stepper motor stage for that. My experience is with THz TDS rather than Fourier spectrometet, how repeatable do you need the position to be, is a min increment of 0.1um ok or do you need the reversible position accuracy to be similar?

What's your budget? Thor labs have stepper stages they claim the min distance is 100nm.

Would you care to define what you mean by physical?

This is what I always ponder.

Well that clears that up.

What? This is completely unintelligible. Can you try and explain yourself in as few words as possible.

With arduinos with on chip USB/serial there are prewritten functions to do it. The problem you'll have is coming up with ways to map all the keys to a limited set of inputs. I've not looked into this too much. There must be a more traditional way to do this, there are hundreds of tutorials on building custom keyboards.

Display where? On a computer? What os? What kind of experience do you have? Have you looked at any of the build a keyboard guides? I've never done it and only looked at doing things using arduino to synthesis a keyboard to do more complicated things. Probably overkill for this.