Stephen Hawking did a cute series titled Genius by Stephen Hawking which aired on PBS in 2016. In episode one he showed that time ravel is not possible. I did not care much for the show but he certainly seemed to believe that time travel wasn’t possible.
Since I believe that time is not a thing, I believe there is nothing to travel through.
If you can accept that there is a “now”, which includes the state of everything in the universe, can you not accept that a different “now” would include a different state of everything in the universe? As far as we know, different states of objects are achieved in a cause-and-effect way which is progressive. Unless you can conjure into existence another set of all the objects in the universe for every moment that ever has been or that ever will be, you should not say that any former nor any future configuration of the universe exists.
That is an interesting thought. Time travel (backward) would basically reverse the nature of the universe. Cause/effect would become effect/cause as you traveled backward in time. It would also break several of the laws of thermodynamics. It takes very little energy to combine hydrogen and oxygen and it releases more energy. It takes a lot of energy to separate them. Because of entropy it takes more energy to separate them than you can harness from combining them. But by reversing time you essentially eliminate entropy. Then the amount of energy released when they combine is the exact amount of energy required to separate them. A single molecular reaction isn’t much and you could explain that away by the energy used for time travel, but when you look at the entirety of the universe instead of just two atoms it becomes impossible for you to generate more energy than that to power your time machine.
The end result of this is that you could get more energy out than exists by repeatedly harnessing the same energy over and over again. The same is true with a “portal” where you step through and are in a different place. You could put one end in the deepest part of a large planet with a liquid ocean and the other end at sea level. Water would spray through the portal at incredible pressure because of the pressure difference going instantly from the deepest point on one side of the portal to see level on the other side. If the other side were high up in the atmosphere this water could be used to power many turbines before reaching the surface again.
I suggest you get a good grasp on the fact that the motion of a light source does not add or subtract from the speed of the light emitted from that source. If it did then the speed of light would not be constant. You may want to think of it like this: the light source moves some distance, stops and emits a wave; it moves another distance, stops and emits a wave, and so on and on. Each wave is emitted from a specific point in space and it will travel in a straight line directly away from that point.
If the source of light is inside the box it will travel along with the box. Only if the light source is stationary in relation to the box’ movement will we experience a relativity effect.
Write4U: If the source of light is inside the box it will travel along with the box. Only if the light source is stationary in relation to the box’ movement will we experience a relativity effect.
I obviously have not been able to convince you. I’m not sure what you mean by “relativity effect”. Maybe you are referring to the apparent change in the frequency of the light. If your box moves forward and a light source positioned in the box is in front of you, the apparent frequency of the light will increase (shorter wave length). If that same light is moved to a position behind you the apparent frequency will decrease (longer wave length).
If you have a light source positioned on a side of the box even with you and that source set up so that the emitted light that you can see is confined to a beam and makes a “dot” on your shoulder (a source at the back of a tube) the apparent frequency won’t change but as the speed of the box increases the dot will move towards your back. If you can see the beam (dust in the box) the path will seem to bend towards the rear of the box while the box is accelerating and will seem to remain at a constant rearward angle while the box moves at a constant speed.
The apparent frequency changes for a fixed external light source in front of you or behind you will be the same as those for the internal light sources. As your box moves past a fixed external light source the light that comes through a side window will be at different angles and the apparent frequency change will change with that angle. If the external light source is moving parallel to your box the light will enter the window at an angle dependent upon the distance it is from you and your speed. The apparent frequency change and apparent angle (in the box dust) will also be dependent upon the distance it is from you and your speed.
Imagine a light bulb with degree marks around its circumference such that the 0/360 mark is in the direction of travel. If the bulb moves parallel to you and is directly off to one side, you will see the 270 mark at slow speeds and short distances. As the speed and/or distance increases you will see the marks move away from the 270 mark towards the 360 mark and the bulb will appear to fall behind you. The same is true for a bulb off to the side and some distance ahead of you. You will see the marks move from the 180 mark area towards the 270 mark.
Everything you will observe is quite straightforward and intuitive without invoking relativity.
I haven’t been following this conversation too closely, but think I know where you’re differing here.
This entire conversation is about relativity, or, what something looks like “relative” to a given point of observation. And it looks like you are both right, kind of, but Bob, you’re failing to take relativity into account.
If a light source is moving in a given direction then, yes, the frequency of the light in that direction is shortened and it is at a higher frequency. However, if you, too, are moving in that same direction at the same speed the light source is moving then the frequency you perceive will be lengthened by the same amount it is shortened by from the movement of the light source. This is why Write4U was saying that if the light source is in the box with you, moving with you and, thus, in the same “relative frame of reference” the frequency would not change. It would not, from your relative observation, even though a person sitting still watching you approach in your box would see the wavelength shortened.
Think of it like being shot with a paintball. If the paintball is fired from a moving car as it approaches you just standing there the impact is harder because you have the added momentum of the moving car. But if you and the shooter are both on a train car then you are both moving at the same speed, in the same direction. So there is no added momentum to the impact. The same is true with the light frequency. You see, the frequency of light is not a “set thing”. It’s relative to your frame of reference. If the light source is stationary and it is you who is moving away then the frequency is lengthened exactly the same as it would be if you were stationary and the light source is moving away because you are not measuring the “set frequency” of the light, you are measuring your relative understanding of the frequency from your point of reference.
Write4U, scratch my previous post. Wow, I don’t know why I wrote that the apparent frequency of a light source in front of the person in the box or behind him would appear to be different from the actual frequency. That is wrong. Obviously, if your clock is moving with you, and is directly ahead or behind, you will see it keeping time correctly.
I may work on a better and correct explanation of how objects off to one side of you will appear at speed. It has been quite a while since I went through that exercise. In fact I encourage you to do it.
Widdershins, I do not like your paint ball analogy because you are comparing apples with oranges. I get what you are trying to say and it is correct, I just don’t like how you are saying it. Peace.
Is the only problem with the paintball analogy that the paintball is actually moving at different relative velocities in the different scenarios, while light is traveling at the same velocity regardless of which scenario and where you are in the scenario?
My grade 12 physics in 1989 didn’t cover this and I haven’t read Einstein, so my thoughts on this are pretty low level.
It is a bit of an apples and oranges comparison since one is velocity and the other is frequency, but what I was trying to show was how relativity came into play. It wasn’t supposed to be a comparison with a paintball and light so much as an example of the role relativity plays. At any rate you understood it so I’m going to count it as a success.
3point14rat : Is the only problem with the paintball analogy that the paintball is actually moving at different relative velocities in the different scenarios, while light is traveling at the same velocity regardless of which scenario and where you are in the scenario?
Well, the paintball actually is moving at the same velocity relative to the car whether it is inside or outside. That is the velocity given to it by the paint gun. The paintball picks up a velocity component from the motion of the car so that relative to an observer on the side of the road it moves at the sum of the velocity of the car plus the velocity given to it by the paint gun. The observer on the side of the road will see the paintball moving at the same velocity whether it is inside the car or outside.
Yes, light moves at the same speed regardless of the motion of the light source. The velocity of the observer will affect the apparent velocity of a moving object and the apparent speed of light. The sum of the velocity of the observer plus the velocity of the light source will affect the apparent frequency of the light.
We generally don’t say light has a velocity. Each wave front moves at C directly away from the point in space where the light source generated that particular wave. Unless the wave is restricted in some way, the wave front will move at C away from the source in all directions.
The parts of Einstein’s work that are really difficult for me is the thing he received his Nobel Prize for, the photoelectric effect and the notion of a photon as a particle. I encourage you to tackle relativity first; it makes sense in a mechanical universe.
Regardless of whether or not I agree with his ideas, this post by Bob warms my heart…
Widdershins, you are correct.
Write4U, scratch my previous post. Wow, I don’t know why I wrote that the apparent frequency of a light source in front of the person in the box or behind him would appear to be different from the actual frequency. That is wrong. Obviously, if your clock is moving with you, and is directly ahead or behind, you will see it keeping time correctly.
I may work on a better and correct explanation of how objects off to one side of you will appear at speed. It has been quite a while since I went through that exercise. In fact I encourage you to do it.
Widdershins, I do not like your paint ball analogy because you are comparing apples with oranges. I get what you are trying to say and it is correct, I just don’t like how you are saying it. Peace.
I hope I didn’t blow it this time.
It may sound cheesy, but reading Bob’s humble admission that he was wrong (even if only accidentally) really makes my day. Thank you Bob!
Since the duality of electromagnetic waves is hard to wrap our heads around, no analogy is going to be perfect. So we need to accept the limitations of analogies and only correct them when they really are used incorrectly. The paintball analogy is good because it is limited to relative velocities (paintballs and light are apples and oranges, but since we’re talking about the speed of fruit, it works.)
This is a very interesting thread - thank you. Cinema has it’s own canon of work tackling the fascinating subject of time-travel.
I’m fascinated by the psychology of film, in particular with regard to its healing and transformative potential. So, I compiled a list of interesting films that take on this challenging subject, and thought it might be worth sharing them here. I’d love to hear your thoughts and feedback. Thanks:
TRUSTED TELLER said:How fast do you have to run to time travel?
A brisk walk will allow you to physically slow time down. We all know that @ "c" , time comes to a halt . i.e. there is no mathematical physical permission to travel faster than "c" . It is mathematically forbidden.
So moving from standing “still” to @“c”, slows available time down in direct relation to the speed you’re moving. I guess its all part of the Theory of Relatively in a Mathematically driven universe consisting of “relative values” and “mathematical functions” as inherent universal potentials.