# Several questions about the speed of light

1. How did one came to the constant 299 792 458 m/s?

2. Why this particular number? Why not 521 334 992?

3. Why can't we travel faster than the speed of light?

phinds
Gold Member
Have you done any research on this at all? What have you found out? This is not really a Q&A forum. We're happy to help when you get stuck but you have to make some effort.

fresh_42
Mentor
1. How did one came to the constant 299 792 458 m/s?
By measurement.
2. Why this particular number? Why not 521 334 992?
Because meter and seconds are defined that way.
3. Why can't we travel faster than the speed of light?
It is as it is. That's how our universe is set up.

1. How did one came to the constant 299 792 458 m/s?

2. Why this particular number? Why not 521 334 992?

3. Why can't we travel faster than the speed of light?
Welcome to Physics Forums!

By its SI definition, 1 meter is how far light will travel in 1/299792458th of a second. Finding the value of the speed of light itself can be done many ways (a few of which I've learned at this very moment by looking it up haha). Here's a good reference for now...
https://en.wikipedia.org/wiki/Speed_of_light#Measurement

Perhaps you could do some research and come back with an answer to your own question for number 3... happy learning

Have you done any research on this at all? What have you found out? This is not really a Q&A forum. We're happy to help when you get stuck but you have to make some effort.

My apologies. It is my first time here. I thought it was a Q&A forum.

davenn and Ophiolite
davenn
Gold Member
Welcome to PF

My apologies. It is my first time here. I thought it was a Q&A forum.

no problems, we do like to answer questions but we really like it when the poster has done a little
research on their own and then comes here to clarify any misunderstandings

phinds
ZapperZ
Staff Emeritus
My apologies. It is my first time here. I thought it was a Q&A forum.

It is, but there is also this:

It is a lot easier to address these if we know (i) that you've done your own effort to educate yourself first and (ii) of your background, i.e. what do you know already, what kind of understanding that you have. It is of no use to you and a waste of time to us if we try to explain anything that goes over your head.

Zz.

Ugh, that number/value is more a political decision than a physics accurate one. Photon wave packets vary in speed depending on the environment/medium they pass through with some searchers bragging they can slow it to almost a stop then let it speed up again. This officially settled exact 'approximate' value is needed to preserve sanity bickering in equation/theory solvers but may hinder solving cosmos mysteries as just using an out the box number may conceal factoring in changing light speed from changes in vacuum energy/dark matter/dark energy. or creator's whims : ) Your 'innocent' inquiry exposes one the biggest hang ups of quantum phyics known as "the measurement problem". A semi related question is trying to determine if an element radioactive decay rate changes over time from outside influences.

davenn
Drakkith
Staff Emeritus
Ugh, that number/value is more a political decision than a physics accurate one.

The exact number is merely a convention that we've chosen. Nothing more, nothing less. We can choose to define our units of length and time however we like. We could cut the length of the meter in half and light would then be defined as traveling at twice the value that it does now (in meters/sec). This obviously changes nothing in the physics, it's only a change in the units. A bit like switching between meters and feet.

This officially settled exact 'approximate' value is needed to preserve sanity bickering in equation/theory solvers but may hinder solving cosmos mysteries as just using an out the box number may conceal factoring in changing light speed from changes in vacuum energy/dark matter/dark energy.

Nonsense. The definition of a meter is based on the speed of light because of convenience and the difference in measurement accuracies between measuring time and distance along with the uncertainty present in using a physical object (that can change length with temperature and other effects) as the defined length for the meter. This in no way hinders science and I cannot fathom why you would think it does. It does the opposite in fact, by removing a great deal of uncertainty in the length of a meter.

Note that any change in the speed of light as it travels through different regions of space would still be observable. Defining the meter and the speed of light as we've done so has no effect on this. An experiment that measures the speed of light would result in different values if placed in two regions of space where light moved at different speeds.

Your 'innocent' inquiry exposes one the biggest hang ups of quantum phyics known as "the measurement problem".

I don't see any connection between the measurement problem and the speed of light. The measurement problem is about wave function collapse, which doesn't appear related to the speed of light.

Mister T
Gold Member
1. How did one came to the constant 299 792 458 m/s?

It defines the length of the meter, and the metrologists wanted the value to come as close as possible to the previously-defined length(s).

3. Why can't we travel faster than the speed of light?

Because no matter how hard we try, we can only get arbitrarily close and not even achieve it. Trying harder doesn't solve this problem.

phinds
Gold Member
Ugh, that number/value is more a political decision than a physics accurate one. Photon wave packets vary in speed depending on the environment/medium they pass through with some searchers bragging they can slow it to almost a stop then let it speed up again. This officially settled exact 'approximate' value is needed to preserve sanity bickering in equation/theory solvers but may hinder solving cosmos mysteries as just using an out the box number may conceal factoring in changing light speed from changes in vacuum energy/dark matter/dark energy. or creator's whims : ) Your 'innocent' inquiry exposes one the biggest hang ups of quantum phyics known as "the measurement problem". A semi related question is trying to determine if an element radioactive decay rate changes over time from outside influences.
@Steven Shiver I see that you are new to the forum. You have perhaps mistaken this forum for a social chit-chat forum where you can just throw out whatever comes into your head and see what discussion ensures. This is not that forum. We focus on actual science. Most of what you have said is either just word salad or shows a misunderstanding of science.

1. How did one came to the constant 299 792 458 m/s?

2. Why this particular number? Why not 521 334 992?

3. Why can't we travel faster than the speed of light?
1&2. When I was younger, in the UK, we learned that the speed of light is 186,000 miles per second. Does this help at all? If not, would you agree that light travels at one light year per year?
3. "Why" is not a good question to ask in a science forum.

davenn