If you measure the speed of a car using police radar, are you

The debroglie wavelength of the car is waaaaaaaaaaaaaaaaay too big to make a measurable difference.

>>8444798
But the difference exists?
Why does it happen? Does it happen only with things that involve electromagnetic waves?

>>8444803
The waves he is talking about are material waves not em. It happens because the photon you're sending to the car exchanges momentum with it, however at these levels, given your macroscopic measurement apparatus there'd be noticeable difference.

>>8444815
>there'd be noticeable difference
Did you mean to say that or that there would NOT be noticeable difference because that anon said that effect would not be that much noticeable.

Roughly speaking , are there methods of measurements that do not affect the thing we are measuring (aka "observer effect").

>>8444815
How is photon changing anything when it has 0 grams.

>>8444823
Ops I mistyped it, there'd be no noticeable difference. If you're sending any particle directly to the object in order to observe it then you will eventually be interacting with it and changing its momentum. However, there is a theoretical idea that I know of, which uses interferometers to extinct the need of interaction on measurements, it's a really interesting article I'll look up for you.
>>8444833
Photons are relativistic particles, although they do not posses rest mass, they do possess momentum.

>>8444833
Photons have energy and momentum even if they have no rest mass. They can transfer some of that energy to the car

>>8444845
>>8444823
Here's the article I told you, the problem is called "Elitzur-Vaidman bomb testing", it's a famous article where they show how to test a bomb without ever interacting with it. https://drive.google.com/file/d/0BzsAYUX-glW_R1diMWFWSHpJNlU/view?usp=drivesdk

>>8444845
>>8444857
>>8444864
Thank you anons for clarifying things for a noob.
Also thank you for that link.

>>8444864
People like you are why I still come to /sci/

Thanks for the linkery-doo

>>8444803
Short Answer, no.
Technically speaking, yes.

Just by existing you have an impact on it's speed, direction, velocity ect.

Everything in the universe have a gravitational pull on one another. As I'm writing this I have a gravitational pull on you, but the amount that my mass is affecting your gravity is so tiny, that you really couldn't realize how little it's affects you.

tl;dr:
The amount of gravitational pull a rock has on you is so tiny that its not measurable.

>>8444796
Yes.

Assuming you're in vacuum, the car is a perfect mirror moving perpendicular to you and you have a spatially coherent light beam pointed directly at the car, then depending on the car's speed you get a momentum change.

It's really tiny.

IRL the only chance to make a difference in speed is by ablating the car's paint with an extremely powerful pulsed IR laser.

Or you can use a 100 GW radar or something that'll vaporise the car and disperse it, thus increasing air friction and stopping it.